Computational Geomechanics : Scipedia

A coupled FEM-DEM procedure for predicting blasting operations in tunnels
F. Zarate, J. Gonzalez, J. Miquel, R. Lohner, E. Oñate

Underground Space (2018). Vol. 3 (3), pp. 310-316

Abstract
We present recent developments in the coupling of the finite element method (FEM) and the discrete element method (DEM) for analysis of rock blasting operations in tunnels. The coupled FEM-DEM technique has proven to be an efficient technique for predicting the multi-fracture of rock induced by the loads generated in blasting situations. The coupled FEM-DEM procedure is applied in the tunnel construction, as well as to gas pressure blasting pyrotechnics situations to break rock for excavation of the tunnel front. In the latter case the effect of gas explosion is modelled by solving with the FEM the equations of gas dynamics in the analysis domain. The effect of the gas forces in the underlying rock mass is modelled with an embedded fluid-structure interaction method. This allows us to accurately predicting the progressive multi-fracture of the rock accounting for the penetration of the gas in the fractured domain modelled with the FEM-DEM procedure. The efficiency of the coupled FEM-DEM technique is demonstrated in several examples of fracture tests and rock blasting problems related to tunnel engineering'''.''' The examples presented show that the combination of the DEM with simple 3-noded linear triangular elements correctly captures the onset of fractures and their evolution [1].
Abstract
We present recent developments in the coupling of the finite element method (FEM) and the discrete element method (DEM) for analysis of rock blasting operations in tunnels. [...]
- 232
- 5/5
- read
A three dimensional FEM-DEM technique for predicting the evolution of fracture in geomaterials and concrete
F. Zarate, A. Cornejo Velázquez, E. Oñate

Comp. Part. Mech (2018). (prepint) Vol. 5 (3) , pp. 411-420

Abstract
This paper extends to three dimensions (3D) the computational technique developed by the authors in 2D for predicting the onset and evolution of fracture in a finite element mesh in a simple manner based on combining the finite element method (FEM) and the discrete element method (DEM) approach Zarate2D. Once a crack is detected at an element edge, discrete elements are generated at the adjacent element vertexes and a simple DEM mechanism is considered in order to follow the evolution of the crack. The combination of the DEM with simple 4-noded linear tetrahedron elements correctly captures the onset of fracture and its evolution, as shown in several 3D examples of application.
Abstract
This paper extends to three dimensions (3D) the computational technique developed by the authors in 2D for predicting the onset and evolution of fracture in a finite element [...]
- 104
- read
Dynamic modelling of retrogressive landslides with emphasis on the role of clay sensitivity
X. Zhang, S. Sloan, E. Oñate

Int. Journal for Numerical and Analytical Methods in Geomechanics (2018). Vol. 42, pp. 1806-1822 (preprint)

Abstract
This paper presents a detailed numerical study of the retrogressive failure of landslides in sensitive clays. The dynamic modelling of the landslides is carried out using a novel continuum approach, the particle finite element method, complemented with an elastoviscoplastic constitutive model. The multiwedge failure mode in the collapse is captured successfully, and the multiple retrogressive failures that have been widely observed in landslides in sensitive clays are reproduced with the failure mechanism, the kinematics, and the deposition being discussed in detail. Special attention has been paid to the role of the clay sensitivity on each retrogressive failure as well as on the final retrogression distance and the final run‐ out distance via parametric studies. Moreover, the effects of the viscosity of sensitive clays on the failure are also investigated for different clay sensitivities.
Abstract
This paper presents a detailed numerical study of the retrogressive failure of landslides in sensitive clays. The dynamic modelling of the landslides is carried out [...]
- 35
- read
Particle finite element modelling of retrogressive slope failure in sensitive clays
X. Zhang, D. Sloan

15th IACMAG (2017). paper no 868

Abstract
In this paper, the slope failure in sensitive clays is studied numerically using the particle finite element method which is a novel approach capable of tackling extreme deformation problems. The sensitive clay is described using an elastoviscoplastic model with strain softening. This model can be considered a mixture of the Tresca model with strain softening and the classical Bingham model. The former is used to capture the solid-like behaviour, for example when the clay is intact, whereas the latter is to describe the semi-fluid behaviour of the fully remolded clay. The complete process of the collapse of a sensitive clay deposit is captured successfully and the widely-observed retrogressive failure mode is reproduced. The mechanism behind the failure is also discovered.
Abstract
In this paper, the slope failure in sensitive clays is studied numerically using the particle finite element method which is a novel approach capable of tackling extreme deformation [...]
- 26
- read
A framework for the behaviour of unsaturated expansive clays
A. Gens, E. Alonso

Canadian Geotechnical Journal (1992). Vol. 29 (6), pp. 761-773

Abstract
The paper presents a framework for describing the mechanical behaviour of unsaturated expansive clays. It is an extension of an existing formulation developed for unsaturated soils of low activity. The extended framework is based on the distinction within the material of a microstructural level where the basic swelling of the active minerals takes place and a macrostructural level responsible for major structural rearrangements. By adopting simple assumptions concerning the coupling between the two levels, it is possible to reproduce major features of the behaviour of unsaturated expansive clays. Some selected qualitative comparisons between model predictions and experimental results reported in the literature are presented. Despite the simplified hypotheses made, a very encouraging agreement is obtained.
Abstract
The paper presents a framework for describing the mechanical behaviour of unsaturated expansive clays. It is an extension of an existing formulation developed for unsaturated [...]
- 22
- read
Data-MSCA-IF: Sensitive clays
X. Zhang

Papers Repository of the International Centre for Numerical Methods in Engineering (CIMNE) (2018). 6

Abstract
Properties of Norwegian clays, Canadian clays and offshore clays
- 20
- read
Data-MSCA-IF: Collapse Velocity
X. Zhang

Papers Repository of the International Centre for Numerical Methods in Engineering (CIMNE) (2018). 7

Abstract
Variations of horizontal and vertical velocities of retrogressive landslides
- 18
- read
Soil-structure interaction simulation of landslides impacting a structure using an implicit material point method
B. Chandra, A. Larese, I. Iaconeta, R. Rossi, R. Wüchner

2nd International Conference on the Material Point Method for Modelling Soil-Water-Structure Interaction

Abstract
Global warming and climate changes have been one of the many causes that triggered numerous catastrophic landslide and mudflow disasters in the past twenty years. The increase of earth temperature has contributed to the increase of precipitation and undisputedly affected the soil slope stability, which by further may cause landslides in various scale and speed. This large soil deformation phenomenon carries along huge rocks and heavy materials that often results in extensive damage in civil infrastructures both directly or indirectly. Coming with this motivation, a soil-structure interaction simulation based on the implicit material point method (MPM) has been implemented within the Kratos Multiphysics framework for the objective of predicting structural deformation and, furthermore, structural failure caused by environmental flow problems such as landslides. In the current study, the soil is modeled using a non-associated Mohr-Coulomb-based elastoplastic law, while the structure is modeled as elastic and Neo-Hookean hyperelastic materials. In the numerical tests conducted, the equivalent stress and displacement measured on both rigid and flexible structures show a good qualitative agreement. In the future works, a more adequate consideration of the soil and structural model will be investigated before conducting a real-scale landslide simulation.
Abstract
Global warming and climate changes have been one of the many causes that triggered numerous catastrophic landslide and mudflow disasters in the past twenty years. The increase [...]
- 18
- read
Modelling of tunnelling processes and rock cutting tool wear with the particle finite element method
J. Carbonell, E. Oñate, B. Suarez

Computational Mechanics (2013). Vol. 52 (3), pp. 607-629

Abstract
Underground construction involves all sort of challenges in analysis, design, project and execution phases. The dimension of tunnels and their structural requirements are growing, and so safety and security demands do. New engineering tools are needed to perform a safer planning and design. This work presents the advances in the particle finite element method (PFEM) for the modelling and the analysis of tunneling processes including the wear of the cutting tools. The PFEM has its foundation on the Lagrangian description of the motion of a continuum built from a set of particles with known physical properties. The method uses a remeshing process combined with the alpha-shape technique to detect the contacting surfaces and a finite element method for the mechanical computations. A contact procedure has been developed for the PFEM which is combined with a constitutive model for predicting the excavation front and the wear of cutting tools. The material parameters govern the coupling of frictional contact and wear between the interacting domains at the excavation front. The PFEM allows predicting several parameters which are relevant for estimating the performance of a tunnelling boring machine such as wear in the cutting tools, the pressure distribution on the face of the boring machine and the vibrations produced in the machinery and the adjacent soil/rock. The final aim is to help in the design of the excavating tools and in the planning of the tunnelling operations. The applications presented show that the PFEM is a promising technique for the analysis of tunnelling problems.
Abstract
Underground construction involves all sort of challenges in analysis, design, project and execution phases. The dimension of tunnels and their structural requirements are [...]
- 15
- read
THM-coupled finite element analysis of frozen soil: formulation and application
S. Nishimura, A. Gens, S. Olivella, R. Jardine

Géotechnique (2009). Vol. 59 (3), pp. 159-171

Abstract
A fully coupled thermo-hydro-mechanical (THM) finite element (FE) formulation is presented that considers freezing and thawing in water-saturated soils. The formulation considers each thermal, hydraulic and mechanical process, and their various interactions, through fundamental physical laws and models. By employing a combination of ice pressure, liquid pressure and total stress as state variables, a new mechanical model has been developed that encompasses frozen and unfrozen behaviour within a unified effective-stress-based framework. Important frozen soil features such as temperature and porosity dependence of shear strength are captured inherently by the model. Potential applications to geotechnics include analysis of frost heave, foundation stability or mass movements in cold regions. The model's performance is demonstrated with reference to the in situ pipeline frost heave tests conducted by Slusarchuk et al. Detailed consideration is given to FE mesh design, the influence of hydraulic parameters, and the treatment of air/ground interface boundary conditions. The THM simulation is shown to reproduce, with fair accuracy, the observed pipeline heave and the porosity growth driven by water migration.
Abstract
A fully coupled thermo-hydro-mechanical (THM) finite element (FE) formulation is presented that considers freezing and thawing in water-saturated soils. The formulation considers [...]
- 15
- read
Benchmarks for geotechnical modeling
E. Alarcón, E. Alonso, D. Aubry, K. Axelsson, E. Oñate

Int. J. Numer. Meth. Engng. (1988). Vol. 26 (11), pp. 2559-2568

Abstract
This letter represents an initiative started by a number of researchers signed below who are working in the field of numerical modelling of soil mechanics problems. We belive that the type of approach outlined is important in a serious numerical study of all problems in geomechanics and indeed is valid in other areas.
Abstract
This letter represents an initiative started by a number of researchers signed below who are working in the field of numerical modelling of soil mechanics problems. We belive [...]
- 14
- read
A multiresolution strategy for solving landslides using the Particle Finite Element Method
P. Becker, S. Idelsohn

Acta Geotechnica (2016). Vol. 11 (3), pp. 643-657

Abstract
We present an approach for the simulation of landslides using the Particle Finite Element Method of the second generation. In this work, the multiphase nature (granular phase and water) of the phenomenon is considered in a staggered fashion using a single, indeformable Finite Element mesh. A fractional step and a monolithic strategy are used for the water flow and granular phase, respectively. In this way, the maximum accuracy with minimal computational times is reached. The method is completed by adding the interaction terms due to drag and pressure forces, together with a moving mesh strategy to reduce the size of the computational domain.
Abstract
We present an approach for the simulation of landslides using the Particle Finite Element Method of the second generation. In this work, the multiphase nature (granular phase [...]
- 14
- read
Sphericity measures of sand grains
R. Rorato, M. Arroyo, E. Andò, A. Gens

Engineering Geology (2019). Vol. 254, pp. 43-53

Abstract
The sphericity of a grain should measure the similitude of its shape with that of a sphere. Sphericity is a shape descriptor of long-standing interest for sedimentology. Now it has gained also interest to facilitate discrete element modelling of granular materials. True sphericity was initially defined by a surface ratio that requires three-dimensional (3D) grain surface measurement. That kind of measurement has been practically impossible until recently and, as a consequence, a number of alternative 3D measures and 2D proxies were proposed. In this work we present results from a study of grain shape based on x-ray tomography of two different sand specimens, containing more than 110.000 particles altogether. Sphericity measures were systematically obtained for all grains. 2D proxy measures were also obtained in samples of oriented and not-oriented grains. It is shown that the 2D proxy best correlated with true sphericity is perimeter sphericity, whereas the traditional Krumbein-Sloss chart proxy is poorly correlated. 2D measures acquired through minor axis projection are more closely related to 3D measures than those acquired using random projections.
Abstract
The sphericity of a grain should measure the similitude of its shape with that of a sphere. Sphericity is a shape descriptor of long-standing interest for sedimentology. [...]
- 13
- read
Soil-environment interactions in geotechnical engineering
A. Gens

Géotechnique (2010). Vol. 60 (1), pp. 3-74

Abstract
The range of problems that geotechnical engineers must face is increasing in complexity and scope. Often, complexity arises from the interaction between the soil and the environment – the topic of this lecture. To deal with this type of problem, the classical soil mechanics formulation is progressively generalised in order to incorporate the effects of new phenomena and new variables on soil behaviour. Recent advances in unsaturated soil mechanics are presented first: it is shown that they provide a consistent framework for understanding the engineering behaviour of unsaturated soils, and the effects of suction and moisture changes. Building on those developments, soil behaviour is further explored by considering thermal effects for two opposite cases: high temperatures, associated with the problem of storage and disposal of high-level radioactive waste; and low temperatures in problems of freezing ground. Finally, the lecture examines some issues related to chemical effects on soils and rocks, focusing in part on the subject of tunnelling in sulphate-bearing rocks. In each case new environmental variables are identified, enhanced theoretical formulations are established, and new or extended constitutive laws are presented. Particular emphasis is placed on mechanical constitutive equations, as they are especially important in geotechnical engineering. The lecture includes summary accounts of a number of case histories that illustrate the relevance and implications of the developments described for geotechnical engineering practice.
Abstract
The range of problems that geotechnical engineers must face is increasing in complexity and scope. Often, complexity arises from the interaction between the soil and [...]
- 12
- read
Numerical modelling of landslide‐generated waves with the particle finite element method (PFEM) and a non‐Newtonian flow model
F. Salazar, J. Irazábal González, A. LARESE, E. Oñate

Int. J. Numer. Anal. Meth. Geomech. (2016). Vol. 40 (6), pp. 809-826

Abstract
Landslide‐generated impulse waves may have catastrophic consequences. The physical phenomenon is difficult to model because of the uncertainties in the kinematics of the mobilised material and to the intrinsic complexity of the fluid–soil interaction. The particle finite element method (PFEM) is a numerical scheme that has successfully been applied to fluid–structure interaction problems. It uses a Lagrangian description to model the motion of nodes (particles) in both the fluid and the solid domains (the latter including soil/rock and structures). A mesh connecting the particles (nodes) is re‐generated at every time step, where the governing equations are solved. Various constitutive laws are used for the sliding mass, including rigid solid and the Newtonian and non‐Newtonian fluids. Several examples of application are presented, corresponding both to experimental tests and to actual full‐scale case studies. The results show that the PFEM can be a useful tool for analysing the risks associated with landslide phenomena, providing a good estimate to the potential hazards even for full‐scale events.
Abstract
Landslide‐generated impulse waves may have catastrophic consequences. The physical phenomenon is difficult to model because of the uncertainties in the kinematics of the [...]
- 10
- read
Modeling of ground excavation with the particle finite-element method
J. Carbonell, E. Oñate, B. Suarez

Journal of Engineering Mechanics (2010). Vol. 136 (4), pp. 455-463

Abstract
An excavation process is a nonlinear dynamic problem that includes geometrical, material, and contact nonlinearities. The simulation of ground excavation has to face contact interaction in a changing geometry composed by several solid domains. The particle finite-element method (PFEM) is based on a Lagrangian description for modeling the motion of a continuum medium. The PFEM is particularly suitable for modeling a fluid motion with free surfaces. The application of the PFEM in ground excavation includes the use of the remeshing process, α-shape concepts for detecting the domain boundary, contact mechanics laws, material constitutive models, and surface wear models. Everything is correctly matched to quantify the excavation and the corresponding damage caused to the ground. The erosion and wear parameters of the soil/rock material govern the evolution of the excavation process. The preliminary results presented in this paper show that the PFEM it is a very suitable tool for the simulation of ground excavation processes.
Abstract
An excavation process is a nonlinear dynamic problem that includes geometrical, material, and contact nonlinearities. The simulation of ground excavation has to face contact [...]
- 10
- read
Desarrollo de un modelo elastoplástico para suelos no saturados
E. Alonso, A. Gens, A. Josa

Boletin de la Sociedad Española de Mecánica de Suelos y Cimentaciones (1993). Vol. 109, pp. 3-28

Abstract
En este artículo se presenta un modelo elastoplástico para describir el comportamiento tenso-deformacional de los suelos no saturados. La formulación se ha realizado en el marco de la teoría de la plasticidad con rigidización isótropa, empleando dos variables tensionales independientes, la presión media neta y la succión. El modelo es capaz de reproducir, de forma consistente y unificada, gran parte de las características fundamentales del comportamiento de los suelos no saturados que anteriormente habían sido tratadas de forma inconexa. Debido a que la información experimental es relativamente escasa, el planteamiento se ha realizado de forma simple con objeto de que sirva de base para posibles extensiones futuras. El modelo se ha desarrollado para suelos no saturados poco o moderadamente expansivos y se transforma en un modelo convencional de estado crítico al alcanzarse la saturación. En el artículo se presentan las formulaciones para estados isótropos y triaxiales, se describen las predicciones típicas para dichos estados y se las compara, de manera cualitativa, con las tendencias características del comportamiento de los suelos no saturados. Posteriormente se emplean los resultados de un conjunto de ensayos de laboratorio con succión controlada, realizados con un caolín y con una arena arcillosa, con objeto de evaluar la capacidad del modelo para reproducir cuantitativamente los comportamientos observados. El ajuste obtenido entre los resultados experimentales y los calculados es considerado satifactorio y confirma la posibilidad de reproducir las características más importantes del comportamiento de los suelos no saturados utilizando un marco de referencia general y sencillo.
Abstract
En este artículo se presenta un modelo elastoplástico para describir el comportamiento tenso-deformacional de los suelos no saturados. La formulación [...]
- 10
- read
Evaluation of a constitutive model for clays and sands: Part II - clay behaviour
J. Pestana, A. Whittle, A. Gens

International Journal for Numerical and Analytical Methods in Geomechanics (2002). Vol. 26 (11), pp. 1123-1146

Abstract
The undrained response of cohesive soils is of paramount importance in geomechanics and it has beenmodelled extensively for the last 50 years. In comparison, drained behaviour of clays has received onlymodest attention. Drained and undrained behaviour is signi¿cantly affected by past consolidation stresshistory. This paper evaluates the capabilities of the MIT-S1 effective stress model, described in acompanion paper, for predicting the anisotropic stress–strain–strength behaviour of clays. The paperillustrates the selection of model parameters for Lower Cromer Till, using data from standard types oflaboratory tests. Comparison of model simulations with measured response for Lower Cromer Till andBoston Blue Clay illustrate model capabilities. The work focuses initially on comparisons of modelpredictions with measurements from undrained triaxial and plane strain tests on initially K0-consolidatedspecimens. Comparisons with measured data from undrained shear tests performed in different modes ofshearing for LCT and BBC show that the model: (a) gives excellent predictions of maximum shear stressconditions and accurately describes the non-linear shear stress–strain behaviour; (b) accurately describesthe anisotropic shear stress–strain–strength conditions for different consolidation stress histories; and(c) gives realistic description of mobilized friction angles, especially at large OCR’s. The paper then focuseson the effects of consolidation stress history for isotropically consolidated specimens of resedimentedLower Cromer Till and Boston Blue Clay. Finally, the paper compares model predictions for drained sheartests on K0and isotropically consolidated specimens with overconsolidation ratios, OCR410; used toevaluate particular aspects of the critical state framework of soil behaviour. Overall, the model givesexcellent predictions of the effect of initial anisotropy and overconsolidation stress history on the shearstress–strain and volumetric behaviour of clays.
Abstract
The undrained response of cohesive soils is of paramount importance in geomechanics and it has beenmodelled extensively for the last 50 years. In comparison, drained behaviour [...]
- 10
- read
Water permeability, water retention and microstructure of unsaturated compacted Boom clay
E. Alonso, J. Vaunat, A. Gens

Engineering Geology (1999). Vol. 54 (1-2), pp. 117-127

Abstract
Three classes of experiments are considered in this paper to provide information for two artificially prepared Boom clay fabrics: mercury intrusion/extrusion tests; main wetting/drying paths; and water inflow/outflow transient (permeability) tests. These tests, which are usually treated separately, are joined in a common reference frame to provide information about the morphology of the porous medium and factors influencing Boom clay unsaturated hydraulic states with reference to water retention curves and relative water permeability values. The main objective is to interpret mercury intrusion porosimetry results in order to define an entrance pore size region at ca 130 to 180 nm separating intra-aggregate and inter-aggregate zones. This pore size region is further associated to a delimiting zone in the retention curve separating regions of ‘intra-aggregate governing suction’ at gravimetric water contents lower than 13–15% (gravimetric water content is not affected by mechanical effects) and ‘inter-aggregate governing suction’ (gravimetric water content is sensible to mechanical actions). This water content is further used to define a threshold zone around a relative water permeability of kw/kws=0.01 delimiting a zone of greater water relative permeability from others that present a restricted flow in a generalised Darcian sense. All these results are consistent with the existence of two main pore size regions: an intra-aggregate porosity with quasi-immobile water that is little affected by loading processes and an inter-aggregate porosity for which the loading mechanism results in a reduction of interconnected macropores affecting free water. Testing results show that intra-aggregate water represents between 54 and 59% of the total volume of water in soil in a low-porosity packing compacted at a dry unit weight of 16.7 kN m-3, whereas it corresponds to ca 28 and 38% in the case of a high-porosity packing compacted at a dry unit weight of 13.7 kN m-3.
Abstract
Three classes of experiments are considered in this paper to provide information for two artificially prepared Boom clay fabrics: mercury intrusion/extrusion tests; main wetting/drying [...]
- 9
- read
A constitutive model for partially saturated soils
E. Alonso, A. Gens, A. Josa

Geotechnique (1990). Vol. 40 (3), pp. 405-430

Abstract
The Paper presents a constitutive model for describing the stress-strain behaviour of partially saturated soils. The model is formulated within the framework of hardening plasticity using two independent sets of stress variables: the excess of total stress over air pressure and the suction. The model is able to represent, in a consistent and unified manner, many of the fundamental features of the behaviour of partially saturated soils which had been treated separately by previously proposed models. On reaching saturation, the model becomes a conventional critical state model. Because experimental evidence is still limited, the model has been kept as simple as possible in order to provide a basic framework from which extensions are possible. The model is intended for partially saturated soils which are slightly or moderately expansive. After formulating the model for isotropic and triaxial stress states, typical predictions are described and compared, in a qualitative way, with characteristic trends of the behaviour of partially saturated soils. Afterwards, the results of a number of suction-controlled laboratory tests on compacted kaolin and a sandy clay are used to evaluate the ability of the model to reproduce, quantitatively, observed behaviour. The agreement between observed and computed results is considered satisfactory and confirms the possibilities of reproducing the most important features of partially saturated soil behaviour using a simple general framework.
Abstract
The Paper presents a constitutive model for describing the stress-strain behaviour of partially saturated soils. The model is formulated within the framework of hardening [...]
- 9
- read
Analysis of the discharge capacity of radial-gated spillways using CFD and ANN – Oliana Dam case study
F. Salazar, R. Morán Moya, R. Rossi, E. Oñate

Journal of Hydraulic Research (2013). (preprint) Vol. 51 (3), pp. 244-252

Abstract
The paper focuses on the analysis of radial-gated spillways, which is carried out by the solution of a numerical model based on the finite element method (FEM). The Oliana Dam is considered as a case study and the discharge capacity is predicted both by the application of a level-set-based free-surface solver and by the use of traditional empirical formulations. The results of the analysis are then used for training an artificial neural network to allow real-time predictions of the discharge in any situation of energy head and gate opening within the operation range of the reservoir. The comparison of the results obtained with the different methods shows that numerical models such as the FEM can be useful as a predictive tool for the analysis of the hydraulic performance of radial-gated spillways.
Abstract
The paper focuses on the analysis of radial-gated spillways, which is carried out by the solution of a numerical model based on the finite element method (FEM). The Oliana [...]
- 7
- read
Turbulent separated shear flow control by surface plasma actuator: experimental optimization by genetic algorithm approach
N. Benard, J. Pons Prats, J. Periaux, G. Bugeda, P. Braud, J. Bonnet, E. Moreau

Experiments in Fluids (2016). (preprint) Vol. 57 (2), pp. 1-17

Abstract
The potential benefits of active flow control are no more debated. Among many others applications, flow control provides an effective mean for manipulating turbulent separated flows. Here, a nonthermal surface plasma discharge (dielectric barrier discharge) is installed at the step corner of a backward-facing step (U 0 = 15 m/s, Re h = 30,000, Re θ = 1650). Wall pressure sensors are used to estimate the reattaching location downstream of the step (objective function #1) and also to measure the wall pressure fluctuation coefficients (objective function #2). An autonomous multi-variable optimization by genetic algorithm is implemented in an experiment for optimizing simultaneously the voltage amplitude, the burst frequency and the duty cycle of the high-voltage signal producing the surface plasma discharge. The single-objective optimization problems concern alternatively the minimization of the objective function #1 and the maximization of the objective function #2. The present paper demonstrates that when coupled with the plasma actuator and the wall pressure sensors, the genetic algorithm can find the optimum forcing conditions in only a few generations. At the end of the iterative search process, the minimum reattaching position is achieved by forcing the flow at the shear layer mode where a large spreading rate is obtained by increasing the periodicity of the vortex street and by enhancing the vortex pairing process. The objective function #2 is maximized for an actuation at half the shear layer mode. In this specific forcing mode, time-resolved PIV shows that the vortex pairing is reduced and that the strong fluctuations of the wall pressure coefficients result from the periodic passages of flow structures whose size corresponds to the height of the step model.
Abstract
The potential benefits of active flow control are no more debated. Among many others applications, flow control provides an effective mean for manipulating turbulent separated [...]
- 7
- read
A stable mesh-independent approach for numerical modelling of structured soils at large strains
L. Monforte, M. Ciantia, J. Carbonell, M. Arroyo, A. Gens

Computers and Geotechnics (2019). Vol. 116, pp. 103215-1/103215-14

Abstract
We describe the large strain implementation of an elasto-plastic model for structured soils into G-PFEM, a code developed for geotechnical simulations using the Particle Finite Element Method. The constitutive model is appropriate for naturally structured clays, cement-improved soils and soft rocks. Structure may result in brittle behavior even in contractive paths; as a result, localized failure modes are expected in most applications. To avoid the pathological mesh-dependence that may accompany strain localization, a nonlocal reformulation of the model is employed. The resulting constitutive model is incorporated into a numerical code by means of a local explicit stress integration technique. To ensure computability this is hosted within a more general Implicit-Explicit integration scheme (IMPLEX). The good performance of these techniques is illustrated by means of element tests and boundary value problems.
Abstract
We describe the large strain implementation of an elasto-plastic model for structured soils into G-PFEM, a code developed for geotechnical simulations using the Particle Finite [...]
- 7
- read
An interface element formulation for the analysis of soil-reinforcement interaction
A. Gens, I. Carol, E. Alonso

Computers and Geotechnics (1989). Vol. 7 (1-2), pp. 133-151

Abstract
The formulation of a family interface elements belonging to the zero-thickness class is briefly described. The formulation is isoparametric and can be applied to 2-D and 3-D analysis. A flexible constitutive law, based on elastoplasticity, describing the mechanical behaviour of the interface is presented. In order to assess the suitability of the elements for the analysis of soil-reinforcement interaction, they are employed in the simulation of a pull-out test in two and three dimensions. It is shown that the performance of the elements can depend strongly on the type of integration rule adopted. The use of integration schemes, such as that of Newton-Cotes, which result in the uncoupling of the degrees of freedom of the element is shown to be very advantegeous. An application to the analysis of a problem involving softening behaviour of the interface is also included.
Abstract
The formulation of a family interface elements belonging to the zero-thickness class is briefly described. The formulation is isoparametric and can be applied to 2-D and [...]
- 7
- read
Ensayos de suelos parcialmente saturados con control simultáneo de succión y temperatura
E. Romero, A. Gens, A. Lloret

Ingeniería Civil (Madrid) (2002). Vol. 127, pp. 115-120

Abstract
En el artículo se presentan algunos avances en técnicas experimentales relacionadas con la caracterización termo-hidro-mecánica de suelos parcialmente saturados. Se describen los principales problemas asociados con la aplicación de la técnica de traslación de ejes a temperaturas elevadas. Se presentan algunos resultados experimentales de trayectorias no isotérmicas a succión matricial impuesta efectuadas sobre diferentes muestras de arcilla preparadas artificialmente.
Abstract
En el artículo se presentan algunos avances en técnicas experimentales relacionadas con la caracterización termo-hidro-mecánica de suelos parcialmente [...]
- 7
- read
Thermo-hydro-mechanical model of the Canister Retrieval Test
M. Zandarin, A. Gens, S. Olivella, E. Alonso

Physics and Chemistry of the Earth (2011). Vol. 36 (17-18), pp. 1806-1816

Abstract
The paper presents a 2-D axisymmetric numerical simulation of the Canister Retrieval Test (CRT). The main objectives of this analysis are the study of the canister–buffer and buffer–host rock interfaces; and the evaluation of the mathematical models used to predict the THM behaviour of the buffer and interface. The THM simulation was performed using the finite element program Code-Bright. The constitutive law adopted to represent the mechanical behaviour of bentonite and pellets is the Barcelona Basic Model (BBM) with a non-linear elastic component accounting for swelling. A joint element with a non-linear elastic mechanical law was implemented in the code for the simulation of the opening–closure of the interface canister–buffer. The formulation of this element also incorporates appropriate thermal and hydraulic laws. The evolution of temperatures, relative humidities and stresses recorded during the test were compared with the simulation results. Comparing the results measured in situ with the results of numerical analysis shows that the formulation used is able to reproduce satisfactorily the phenomena involved in the test as well as their interactions. In addition, the final dry density and degree of saturation measured in samples of bentonite and pellets extracted during the test dismantling were also in agreement with the calculated values.
Abstract
The paper presents a 2-D axisymmetric numerical simulation of the Canister Retrieval Test (CRT). The main objectives of this analysis are the study of the canister–buffer [...]
- 7
- read
Aznalcóllar dam failure. Part 1: field observations and material properties
E. Alonso, A. Gens

Géotechniques (2006). Vol. 56 (3), pp. 165-183

Abstract
The paper describes the failure of Aznalcóllar dam, in southern Spain, in April 1998. The rockfill dam slid forward and released a flow of acid-saturated tailings. The geology and geomorphology of the site are described. The results of a detailed laboratory testing programme on the tailings material and on the overconsolidated high-plasticity foundation clay are given. Special attention is paid to the identification of cementation of the tailings and to the strength and consolidation properties of the foundation clay. Failure features are interpreted on the basis of the field evidence, taking into account the measured geotechnical properties of the materials involved.
Abstract
The paper describes the failure of Aznalcóllar dam, in southern Spain, in April 1998. The rockfill dam slid forward and released a flow of acid-saturated tailings. [...]
- 7
- read
Sand production simulation coupling DEM with CFD
N. Climent, M. Arroyo, C. O'Sullivan, A. Gens

European Journal of Environmental and Civil Engineering (2014). Vol. 18 (9), pp. 983-1008

Abstract
Sand production in oil wells is often predicted using continuum fluid-coupled models. However, a continuum approach cannot capture important features of the sanding problem, such as erosion and localised failure. This shortcoming of continuum-based analyses can be overcome using the particulate discrete element method (DEM). However, these models, apart from issues of computational cost, have the disadvantage of being difficult to calibrate. One way forward is to calibrate DEM models to capture the response observed in continuum models, where the material parameters can be selected with greater confidence. Adopting this philosophy here, a 3D numerical model based on DEM coupled with Computational Fluid Dynamics was built to simulate sand production around perforations. In the first instance, the basic DEM model (i.e. a dry case) is calibrated against a well-known poro-elastoplastic analytical solution by Risnes et al. (1982). Subsequently, a range of hydrostatic scenarios involving different levels of pore pressure and effective stress are considered. The numerical model shows an asymmetry of the eroded zone that is related to initial microscale inhomogeneity. The stress peak of the analytical solution at the elastic-plastic interface is smoothed because of that asymmetry. The presence of hydrostatic fluid decreases the plastic region and reduces the amount of sand produced. This is not due to changes in effective stress but rather by the particle-scale stabilizing effect of the fluid drag.
Abstract
Sand production in oil wells is often predicted using continuum fluid-coupled models. However, a continuum approach cannot capture important features of the sanding problem, [...]
- 7
- read
Pruebas de carga horizontal de columnas de suelo tratado mediante «Jet-Grouting»
A. Lloret, E. Alonso, A. Gens

Boletin de la Sociedad Española de Mecánica de Suelos y Cimentaciones (1992). Vol. 105, pp. 2-8

Abstract
La realización de dos pruebas de carga a escala real sobre dos pares de columnas de «jet-grouting», ha proporcionado una interesante oportunidad para constatar la capacidad de los métodos de análisis convencionales para predecir el comportamiento de las columnas. Se ha comprobado que para poder reproducir el comportamiento observado en las columnas mediante las teorías existentes para predecir movimientos horizontales en pilotes, es necesario considerar la disminución exponencial de los módulos de deformación del suelo con el desplazamiento de la cabeza de la columna. Este efecto se mantiene para desplazamientos laterales muy pequeños y es consistente con resultados publicados previamente para grandes desplazamientos. Los ensayos de laboratorio e «insitu» (triaxial, columna resonante y sísmicos de «Crosshole»), son difíciles de usar para la predicción del comportamiento y además proporcionan una información limitada. Las teorías existentes para estudiar el comportamiento lateral de pilotes, son razonablemente capaces de predecir la deformada de la columna y sus momentos flectores cuando se incorpora en el análisis una variación correcta del módulo con la deformación.
Abstract
La realización de dos pruebas de carga a escala real sobre dos pares de columnas de «jet-grouting», ha proporcionado una interesante oportunidad para constatar [...]
- 6
- read
Reply to the discussion by Zhang and Lytton on “A new modelling approach for unsaturated soils using independent stress variables”
D. Sloan, D. Fredlund, A. Gens

Canadian Geotechnical Journal (2008). Vol. 45 (12), pp. 1784-1787

Abstract
We would like to thank the discussers for their interest in our paper and also for their challenging questions, which show their thorough knowledge on the subject. Their comments have enhanced our understanding of the subject area and hopefully may lead to further constitutive model developments.
Abstract
We would like to thank the discussers for their interest in our paper and also for their challenging questions, which show their thorough knowledge on the subject. Their comments [...]
- 6
- read
Unsaturated soils: from constitutive modelling to numerical algorithms
D. Sloan, A. Gens, D. Fredlund, S. Sloan

Computers and Geotechnics (2008). Vol. 35 (6), pp. 810-824

Abstract
This paper presents an overview of constitutive modelling of unsaturated soils and the numerical algorithms for solving the associated boundary value problems. It first discusses alternative stress and strain variables that can be used in constitutive models for unsaturated soils. The paper then discusses the key issues in unsaturated soil modelling and how these issues can be incorporated into an existing model for saturated soils. These key issues include (1) volumetric behaviour associated with saturation or suction changes; (2) strength behaviour associated with saturation and suction changes, and (3) hydraulic behaviour associated with saturation or suction changes. The paper also shows how hysteresis in soil–water characteristics can be incorporated into the elasto-plastic framework, leading to coupled hydro-mechanical models. Finally, the paper demonstrates the derivation of the incremental stress–strain relations for unsaturated soils and discusses briefly the new challenges in implementing these relations into the finite element method.
Abstract
This paper presents an overview of constitutive modelling of unsaturated soils and the numerical algorithms for solving the associated boundary value problems. It first discusses [...]
- 6
- read
A hydro-geochemical analysis of the saturation process with salt water of a bentonite crushed granite rock mixture in an engineered nuclear barrier
C. Mata, L. Guimarães, A. LEDESMA, A. Gens, S. Olivella

Engineering Geology (2005). Vol. 81 (3), pp. 227-245

Abstract
A MX-80 sodium bentonite crushed granite rock mixture is being saturated in the Äspö Hard Rock Laboratory managed by SKB (the Swedish Company of nuclear waste management) as part of the “Backfill and Plug Test Project”. The Äspö Hard Rock Laboratory is placed in the Swedish Island of Äspö, an underground full-scale laboratory where different testing construction procedures and handling techniques are being studied. The groundwater of Äspö has a variable salt concentration according to the zone considered. The added water during the mixing process of both materials had an average salt concentration of 6 g/L. However, backfill is being saturated with salt water containing higher salt content (up to 16 g/L, 50 / 50 of NaCl and CaCl2 by mass) to speed up the saturation process. The mixture swelling capacity is small due to the low backfill bentonite content, but its activity is still large if compared with natural clayey soils. A coupled hydro-chemical approach was used to simulate the backfill hydration process, comparing the results with in situ measurements. An intrinsic permeability law, depending on salt concentration in the liquid phase, was incorporated into the model. The retention curve was also determined taking into account the effect of the chemical species on backfill behaviour. The simulation of the saturation process shows the importance of studying these problems with a HC (hydro-chemical) formulation, especially if long term behaviour of such mixtures is going to be reproduced.
Abstract
A MX-80 sodium bentonite crushed granite rock mixture is being saturated in the Äspö Hard Rock Laboratory managed by SKB (the Swedish Company of nuclear waste management) [...]
- 6
- read
Coupled Thermo-Hydro-Mechanical and Chemical Analysis of Expansive Clay Subjected to Heating and Hydration
L. Guimarães, A. Gens, S. Olivella

Transport in Porous Media (2007). Vol. 66 (3), pp. 341-372

Abstract
A fully coupled formulation combining reactive transport and an existing thermo-hydro-mechanical (THM) code is presented. Special attention has been given to phenomena likely to be encountered in clay barriers used as part of containment systems of nuclear waste. The types of processes considered include hydrolysis, complex formation, oxidation/reduction reactions, acid/base reactions, precipitation/dissolution of minerals and cation exchange. Both kinetically-controlled and equilibrium-controlled reactions have been incorporated. The total analytical concentrations (including precipitated minerals) are adopted as basic transport variables and chemical equilibrium is achieved by minimizing Gibbs Free Energy. The formulation has been incorporated in a general purpose computer code capable of performing numerical analysis of engineering problems. A validation exercise concerning a laboratory experiment involving the heating and hydration of an expansive compacted clay is described.
Abstract
A fully coupled formulation combining reactive transport and an existing thermo-hydro-mechanical (THM) code is presented. Special attention has been given to phenomena likely [...]
- 6
- read
Reply to the Discussion on “Coupled effective stress analysis of insertion problems in geotechnics with the Particle Finite Element method”
L. Monforte, M. Arroyo, J. Carbonell, A. Gens

Computers and Geotechnics (2019). Vol. 109, pp. 209-292

Abstract
The discussers ask why a hyperelastic model was employed. There are several reasons why using an hyper-elastic model is preferable. Probably the most important one is that closed cycles do not produce nor dissipate energy [17, 8]; instead, using a hypoelastic model, closed cycles may produce or dissipate energy, which is inconsistent with the definition of an elastic deformation path. As stressed by Borja et al.[3], the use of an hypoelastic law with constant Poisson’s ratio in the context of the Modified Cam Clay may produce that closed-loop stress paths may result in a non-conservative elastic behavior; therefore, at the end of the loading path the elastic deformation might not be fully recovered. Also, hyper-elastic laws underpin the formulation of large-strain elastoplasticity [17]. By using this theory, the constitutive model is inherently frame-indiferent [17] and algorithmic objective [9].
Abstract
The discussers ask why a hyperelastic model was employed. There are several reasons why using an hyper-elastic model is preferable. Probably the most important one is that [...]
- 5
- read
Performance of mixed formulations for the particle finite element method in soil mechanics problems
L. Monforte, J. Carbonell, M. Arroyo, A. Gens

Comp. Part. Mech (2016). (Preprint) Vol. 4 (3), pp. 269-284

Abstract
This paper presents a computational framework for the numerical analysis of fluid-saturated porous media at large strains. The proposal relies, on one hand, on the particle finite element method (PFEM), known for its capability to tackle large deformations and rapid changing boundaries, and, on the other hand, on constitutive descriptions well established in current geotechnical analyses (Darcy’s law; Modified Cam Clay; Houlsby hyperelasticity). An important feature of this kind of problem is that incompressibility may arise either from undrained conditions or as a consequence of material behaviour; incompressibility may lead to volumetric locking of the low-order elements that are typically used in PFEM. In this work, two different three-field mixed formulations for the coupled hydromechanical problem are presented, in which either the effective pressure or the Jacobian are considered as nodal variables, in addition to the solid skeleton displacement and water pressure. Additionally, several mixed formulations are described for the simplified single-phase problem due to its formal similitude to the poromechanical case and its relevance in geotechnics, since it may approximate the saturated soil behaviour under undrained conditions. In order to use equal-order interpolants in displacements and scalar fields, stabilization techniques are used in the mass conservation equation of the biphasic medium and in the rest of scalar equations. Finally, all mixed formulations are assessed in some benchmark problems and their performances are compared. It is found that mixed formulations that have the Jacobian as a nodal variable perform better.
Abstract
This paper presents a computational framework for the numerical analysis of fluid-saturated porous media at large strains. The proposal relies, on one hand, on the particle [...]
- 5
- read
Permeability and compressibility of slurries from seepage-induced consolidation
A. Huerta, G. Kriegsmann, R. Krizek

Journal of geotechnical engineering (ASCE) (1988). Vol. 114 (5), pp. 614-627

Abstract
A one-dimensional mathematical model based on finite-strain theory is developed to solve the problem of seepage-induced consolidation in sedimented slurries or very soft clays. The direct solution employs known or assumed material property relationships to determine the final thickness of a soft sediment subjected to a constant piezometric head. It is useful for predicting the capacity of a disposal area and the time-dependent improvement in material properties. Alternatively, the inverse solution utilizes final settlement and steady-state flow data from laboratory or field tests to deduce permeability and compressibility relationships for soft sediments. This approach is especially helpful in the case of permeability determinations because it avoids some of the major problems associated with permeability testing of such materials. The resulting model shows that the coefficient of permeability influences both the time to reach the steady-state condition and the nature of the steady-state condition itself. An illustrative example is presented wherein data from a series of tests on a kaolinite slurry are used to establish material property relationships that are then used to predict the response of other tests on the same soil under different conditions
Abstract
A one-dimensional mathematical model based on finite-strain theory is developed to solve the problem of seepage-induced consolidation in sedimented slurries or very soft clays. [...]
- 5
- read
Dimensionless analysis of HSDM and application to simulation of breakthrough curves of highly adsorbent porous media
A. Pérez-Foguet, E. Casoni, A. Huerta

Journal of Environmental Engineering (ASCE) (2013). Vol. 139 (5), pp. 667-676 (Preprint)

Abstract
The homogeneous surface diffusion model (HSDM) is widely used for adsorption modeling of aqueous solutions. The Biot number is usually used to characterize model behavior. However, some limitations of this characterization have been reported recently, and the Stanton number has been proposed as a complement to be considered. In this work, a detailed dimensionless analysis of HSDM is presented and limit behaviors of the model are characterized, confirming but extending previous results. An accurate and efficient numerical solver is used for these purposes. The intraparticle diffusion equation is reduced to a system of two ordinary differential equations, the transport-reaction equation is discretized by using a discontinuous Galerkin method, and the overall system evolution is integrated with a time-marching scheme. This approach facilitates the simulation of HSDM with a wide range of dimensionless numbers and with a correct treatment of shocks, which appear with nonlinear adsorption isotherms and with large Biot numbers and small surface diffusivity modulus. The approach is applied to simulate the breakthrough curves of granular ferric hydroxide. Published experimental data is adequately simulated.
Abstract
The homogeneous surface diffusion model (HSDM) is widely used for adsorption modeling of aqueous solutions. The Biot number is usually used to characterize model behavior. [...]
- 5
- read
Nonisothermal multiphase flow of brine and gas through saline media
S. Olivella, J. Carrera, A. Gens, E. Alonso

Transport in Porous Media (1994). Vol. 15 (3), pp. 271-293

Abstract
We propose a general formulation for nonisothermal multiphase flow of brine and gas through saline media. The balance equations include mass balance (three species), equilibrium of stresses and energy balance (total internal energy). Salt, water and air mass balance equations are established. The balance of salt allows the establishment of the equation for porosity evolution due to solid skeleton deformation, dissolution/precipitation of salt and migration of brine inclusions. Water and air mass balance equations are also obtained. Two equations are required for water: total water in the medium and water present in solid phase brine inclusions. The mechanical problem is formulated through the equation of stress equilibrium. Finally, the balance of internal energy is established assuming thermal equilibrium between phases. Some general aspects of the constitutive theory are also presented.
Abstract
We propose a general formulation for nonisothermal multiphase flow of brine and gas through saline media. The balance equations include mass balance (three species), equilibrium [...]
- 5
- read
Análisis retrospectivo usando un criterio de máxima verosimilitud
A. Ledesma, E. Alonso, A. Gens

Ingeniería Civil (Madrid) (1990). Vol. 76, pp. 49-56

Abstract
El artículo presenta una formulación probabilística del problema del análisis retrospectivo, basado en un criterio de máxima verosimilitud. La formulación está organizada de forma jerárquica, de manera que se pueden considerar análisis de diferente grado de complejidad dentro de un mismo marco teórico. Se presentan dos ejemplos de aplicación. El primero (el depósito de ensayo de Mundford) sólo requiere la adopción de un criterio de optimización de mínimos cuadrados, mientras que para el segundo (excavación de la caverna de la central reversible de Estanygento), es necesario introducir información previa sobre los parámetros y adoptar una expresión para la función objetivo basada en un criterio de optimización de máxima verosimilitud más general. Los ejemplos presentados ilustran las posibilidades de este procedimiento para llevar a cabo análisis retrospectivos.
Abstract
El artículo presenta una formulación probabilística del problema del análisis retrospectivo, basado en un criterio de máxima verosimilitud. [...]
- 5
- read
A stress point algorithm for an elastoplastic model in unsaturated soils
J. Vanuat, J. Cante, A. LEDESMA, A. Gens

International Journal of Plasticity (2000). Vol. 16, pp. 121-141

Abstract
Two stress fields, combination of total stresses, liquid pressure and gas pressure have to be considered to explain the deformational behaviour of unsaturated media. Elastoplastic models developed for these materials consider generally two yield surfaces, each one associated to a stress field, and whose intersection produces a corner in the space of generalised stress components. In this paper, a stress point algorithm is proposed to cope with the integration of such constitutive laws, which can be seen as non smooth multisurface plastic models in the space of the two stress fields. The basic model developed by Alonso et al. (Alonso, E.E., Gens, A., 1990. A constitutive model for partially saturated soils. Géotechnique 40 (3), 405–430), which will be used to test the algorithm, is first described. Generalised stress and strain variables are then defined. Implementation of the return mapping algorithm, based on an implicit integration scheme, is presented with special attention devoted to the problem of mixed control imposed by the F.E. formulation generally used to analyse the hydromechanical behaviour of unsaturated media. Validation results on distinct generalised stress paths are given at the end.
Abstract
Two stress fields, combination of total stresses, liquid pressure and gas pressure have to be considered to explain the deformational behaviour of unsaturated media. Elastoplastic [...]
- 5
- read
Finite element formulation and algorithms for unsaturated soils. Part II: verification and application
D. Sheng, D. Smith, S. Sloan, A. Gens

International Journal for Numerical and Analytical Methods in Geomechanics (2003). Vol. 27, pp. 767-790

Abstract
The finite-element formulation and integration algorithms developed in Part I are used to analyse a number of practical problems involving unsaturated and saturated soils. The formulation and algorithms perform well for all the cases analysed, with the robustness of the latter being largely insensitive to user-defined parameters such as the number of coarse time steps and error control tolerances. The efficiency of the algorithms, as measured by the CPU time consumed, does not depend on the number of coarse time steps, but may be influenced by the error control tolerances. Based on the analyses presented here, typical values for the error control tolerances are suggested. It is also shown that the constitutive modelling framework presented in Part I can, by adjusting one constitutive equation and one or two material parameters, be used to simulate soils that expand or collapse upon wetting. Treating the suction as a strain variable instead of a stress variable proves to be an efficient and robust way of solving suction-dependent plastic yielding. Moreover, the concept of the constitutive stress is a particularly convenient way of handling the transition between saturation and unsaturation.
Abstract
The finite-element formulation and integration algorithms developed in Part I are used to analyse a number of practical problems involving unsaturated and saturated soils. [...]
- 5
- read
Physical modeling of a stepped spillway without sidewalls
S. Estrella, M. Sánchez-Juny, E. Bladé, J. Dolz

Canadian journal of civil engineering (2015). Vol. 42 (5), pp. 311-318

Abstract
The interest of a consulting company in designing stepped spillways in roller compacted concrete (RCC) dams led us to propose the possibility of building this type of spillway without sidewalls. Previous research on stepped spillways has focused on characterizing the complex hydraulic behavior of flow on these structures, as well as design criteria. Such studies have usually been conducted on stepped spillways with a constant width along the spillway, that is, with sidewalls. In the present work, we report the results of the physical modeling of a generic stepped spillway without sidewalls (slope 1v:0.8h). In general terms, the lack of sidewalls produces a lateral expansion of water and therefore a non-uniform longitudinal and transversal discharge distribution. Consequently, the flow type, characteristic water depth, velocity, air concentration, and pressure fields change along and across the spillway. The resulting data demonstrate that the distribution of the different variables studied depend on the specific discharge at the entrance and the spillway height.
Abstract
The interest of a consulting company in designing stepped spillways in roller compacted concrete (RCC) dams led us to propose the possibility of building this type of spillway [...]
- 5
- read
Numerical simulation of undrained insertion problems in geotechnical engineering with the Particle Finite Element Method (PFEM)
L. Monforte, M. Arroyo, J. Carbonell, A. Gens

Computers and Geotechnics (2017). (preprint)Vol. 82, pp. 144-156

Abstract
The paper presents total-stress numerical analyses of large-displacement soil-structure interaction problems in geomechanics using the Particle Finite Element Method (PFEM). This method is characterized by frequent remeshing and the use of low order finite elements to evaluate the solution. Several important features of the method are: (i) a mixed formulation (displacement-mean pressure) stabilized numerically to alleviate the volumetric locking effects that are characteristic of low order elements when the medium is incompressible, (ii) a penalty method to prescribe the contact constraints between a rigid body and a deformable media combined with an implicit scheme to solve the tangential contact constraint, (iii) an explicit algorithm with adaptive substepping and correction of the yield surface drift to integrate the finite-strain multiplicative elasto-plastic constitutive relationship, and (iv) the mapping schemes to transfer information between successive discretizations. The performance of the method is demonstrated by several numerical examples, of increasing complexity, ranging from the insertion of a rigid strip footing to a rough cone penetration test. It is shown that the proposed method requires fewer computational resources than other numerical approaches addressing the same type of problems.
Abstract
The paper presents total-stress numerical analyses of large-displacement soil-structure interaction problems in geomechanics using the Particle Finite [...]
- 4
- read
Surface tension controls the hydraulic fracture of adhesive interfaces bridged by molecular bonds
D. Kaurin, M. Arroyo

Physical review letters (2019). Vol. 123 (22), pp. 1-6 (Preprint)

Abstract
Biological function requires cell-cell adhesions to tune their cohesiveness; for instance, during the opening of new fluid-filled cavities under hydraulic pressure. To understand the physical mechanisms supporting this adaptability, we develop a stochastic model for the hydraulic fracture of adhesive interfaces bridged by molecular bonds. We find that surface tension strongly enhances the stability of these interfaces by controlling flaw sensitivity, lifetime, and optimal architecture in terms of bond clustering. We also show that bond mobility embrittles adhesions and changes the mechanism of decohesion. Our study provides a mechanistic background to understand the biological regulation of cell-cell cohesion and fracture.
Abstract
Biological function requires cell-cell adhesions to tune their cohesiveness; for instance, during the opening of new fluid-filled cavities under hydraulic pressure. To understand [...]
- 4
- read
Estimation of parameters in geotechnical backanalysis. II- Application to a tunnel excavation problem
A. Gens, A. Ledesma, E. Alonso

Computers and Geotechnics (1996). Vol. 18 (1), pp. 29-46

Abstract
A general statistical framework to perform backanalysis in geotechnical problems from field instrumentation has been presented in a companion paper. Here, an application to a real case involving the excavation of a tunnel in stiff overconsolidated clay is described. Both, extensometer and inclinometer measurements are used as input data and elastic moduli of the ground and the value of the K0 coefficient are estimated. The finite element method is used as the computational procedure to solve the direct problem, and has been coupled to the identification algorithm as described in the companion paper. In addition, a discussion on the reliability of the parameters identified is presented.
Abstract
A general statistical framework to perform backanalysis in geotechnical problems from field instrumentation has been presented in a companion paper. Here, an application [...]
- 4
- read
Numerical formulation for a simulator (CODE_BRIGHT) for the coupled analysis of saline media
E. Alonso, S. Olivella, A. Gens, J. Carrera

Transport in Porous Media (1994). Vol. 15 (3), pp. 87-112

Abstract
Presents numerical aspects of the program CODE_BRIGHT, which is a simulator for COupled DEformation, BRIne, Gas and Heat transport problems. It solves the equations of mass and energy balance and stress equilibrium and, originally, it was developed for saline media. The governing equations also include a set of constitutive laws and equilibrium conditions. The main peculiarities of saline media are in the dissolution/precipitation phenomena, presence of brine inclusions in the solid salt and creep deformation of the solid matrix.
Abstract
Presents numerical aspects of the program CODE_BRIGHT, which is a simulator for COupled DEformation, BRIne, Gas and Heat transport problems. It solves the equations [...]
- 4
- read
Hidratación de un relleno compactado que contiene agregados de alta intensidad
E. Alonso, A. Lloret, A. Gens, C. Delahaye, J. Facio

Boletin de la Sociedad Española de Mecánica de Suelos y Cimentaciones (1996). Vol. 121, pp. 3-7

Abstract
Se han investigado, mediante ensayos de laboratorio, las características de hidratación de mezclas expansivas constituídas por una matriz de polvo arcilloso y agregados (pastillas de pequeño tamaño) de arcilla de alta densidad. Estas mezclas se han propuesto como material de relleno para aislar residuos potencialmente contaminantes del medio geológico que los rodea. Se ha simulado el comportamiento de este material de relleno bajo las condiciones existentes "in situ" mediante un analisis hidro-mecánico acoplado. En el análisis, el relleno se caracterizó de acuerdo con los resultados del programa de ensayos de laboratorio. Hydration characteristics of an expansive mixture of compacted clay matrix and high density pellets ha ve been investigated by means of laboratory tests. These mixtures are proposed as a suitable barrier material to isolate hazardous wastes from the surrounding geological environment. The behaviour of this material under conditions prevailing "in situ" has been simulated by means of a coupled flow-deformation analysis. The backfill was characterized according to the results of the laboratory tests program.
Abstract
Se han investigado, mediante ensayos de laboratorio, las características de hidratación de mezclas expansivas constituídas por una matriz de polvo arcilloso [...]
- 4
- read
Modelling the mechanical behaviour of expansive clays
E. Alonso, J. Vaunat, A. Gens

Engineering Geology (1999). Vol. 54 (1-2), pp. 173-183

Abstract
A simple formalism is presented to model the behaviour of expansive clays. Two levels of structure are considered. The behaviour of the macrostructure follows the model developed for unsaturated materials by Alonso et al. [Géotechnique 40 (3) (1990) 405–430]. The behaviour of the microstructure is adapted from the work of Gens and Alonso [Can. Geotech. J. 29 (1992) 1013–1032] in order to include the possibility of the micropores being partially saturated. Mechanical coupling between both levels of structure are defined through two functions, one for wetting and the other for drying. They express the change in macrostructural void ratio due to a change in microstructural void ratio, and their value depends on the state of compaction of the macrostructure. The general shape of these curves is discussed on the basis of experimental evidence. Phenomena such as the dependency of strain on stress–suction path, accumulation of expansion strain during suction cycles at low confining stress, accumulation of compression strain during suction cycles at high confining stress, strain fatigue during drying–wetting cycles, macropore invasion by expanded microstructure and development of macroporosity during strong drying can be represented. A mathematical formulation of the model is described and its performance finally assessed by comparison with laboratory tests.
Abstract
A simple formalism is presented to model the behaviour of expansive clays. Two levels of structure are considered. The behaviour of the macrostructure follows the model developed [...]
- 4
- read
Precompression design for secondary settlement reduction
E. Alonso, A. Gens, A. Lloret

Geotechnique (2000). Vol. 50 (6), pp. 645-656

Abstract
A large water treatment plant is to be built on soft deltaic deposits. Precompression has been selected as the method for achieving the required ground improvement. An instrumented preload test has been carried out to obtain reliable information on precompression performance. Distributions of displacements throughout the foundation depth, obtained using sliding micrometer extensometers, have proved extremely useful for identifying the mechanisms of behaviour controlling ground deformation. The magnitudes of displacements are largely dependent on the overconsolidation state of the soil. As primary consolidation settlements take place rather quickly, they can be largely controlled by applying a preload over a limited period. The main design criterion therefore concerns secondary settlements. Laboratory and field data indicate clearly that overconsolidating the soil, even in moderate amounts, significantly reduces the secondary compression rate. The performance of an unloading stage in the preload test provides crucial information in this regard. Therefore applying a preload surcharge larger than the final structure load is quite effective in controlling the magnitude of subsequent secondary settlements. The information collected during the site investigation and in the preload test provides the basis for the development of a ground deformation model that can be used for computing settlement histories. The model is used as a design tool for the final proposal of the precompression treatment required for the various structures of the plant
Abstract
A large water treatment plant is to be built on soft deltaic deposits. Precompression has been selected as the method for achieving the required ground improvement. An instrumented [...]
- 4
- read
Compacted soil behaviour: initial state, structure and constitutive modelling
E. Alonso, N. Pinyol, A. Gens

Géotechnique (2013). Vol. 63 (6), pp. 463-478

Abstract
The paper explores the behaviour of compacted soils throughout the (dry density–water content) compaction plane by means of a conceptual framework that incorporates microstructural information. The engineering properties of compacted soils are described by an initial state in terms of a yielding stress, soil suction and a microstructural state variable. Microstructure is defined by the ratio of microvoid volume to total void volume. The pattern of variation of the microstructural parameter within the compaction plane has been determined, for some compacted soils, by analysing mercury intrusion porosimetry data. The microstructure of wet and dry compaction conditions can then be quantified. To ensure consistency, the framework is cast in the form of a constitutive model defined in terms of an effective suction and a constitutive stress that incorporate the microstructural variable. The model is shown to be consistent with a number of experimental observations and, in particular, it explains the intrinsic collapse potential of compacted soils. It predicts, for a common initial suction, a higher collapse potential for dry of optimum conditions than for wet compaction. It also predicts in a natural manner the observed evolution of soil compressibility during drained or undrained loading. Model capabilities are illustrated by application to a testing programme on statically compacted samples of low-plasticity silty clay. The compression behaviour of samples compacted wet and dry of optimum and the variation of collapse strains with confining stress have been successfully reproduced by the model.
Abstract
The paper explores the behaviour of compacted soils throughout the (dry density–water content) compaction plane by means of a conceptual framework that incorporates [...]
- 4
- read
Identification of bonded clay parameters in SBPM tests: a numerical study
N. González, M. Arroyo, A. Gens

Soils and Formulation (2009). Vol. 49 (3), pp. 329-340

Abstract
A bonded elasto-plastic soil model is adopted to simulate self-boring pressuremeter tests. Calibration of the model with results from several natural clays identifies a meaningful parameter range for the simulations. Then a systematic sensitivity analysis of the loading SBPM test curve is carried out with an infinite cylindrical cavity analogue, focusing on the variables and parameters that are specific to the bonded material. This analysis reveals that the effects of mechanical overconsolidation and bonding on the pressuremeter loading curves are very similar. Unloading and strain-holding phases of the test show a greater capability to separate mechanical overconsolidation from bonding. The limited effects of finite pressuremeter length and partial drainage on the simulated curves do not change those conclusions.
Abstract
A bonded elasto-plastic soil model is adopted to simulate self-boring pressuremeter tests. Calibration of the model with results from several natural clays identifies [...]
- 4
- read
Factors controlling rock-clay buffer interaction in a radioactive clay repository
A. Gens, L. Guimareas, A. García-Molina, E. Alonso

Engineering Geology (2002). Vol. 64 (2-3), pp. 297-308

Abstract
The paper examines the interaction between host rock and a clay-based engineered barrier in the context of deep underground disposal of high-level radioactive waste. A large scale “in situ” heating test currently under way in the underground Grimsel Rock Laboratory (GRL; Switzerland) is adopted as a representative case for study. The main features of the behaviour of the rock/barrier system have been examined using a comprehensive programme of coupled thermo–hydro–mechanical analyses. A parametric study has been performed to assess the effects of individual phenomena and parameters. The characterisation activities carried out in relation with the in situ test provide the information on material properties and test conditions required. Results highlighting the influence of vapour diffusion, permeability, and retention curve of rock and bentonite are presented. The interaction between clay barrier and host medium exhibits a high degree of complexity.
Abstract
The paper examines the interaction between host rock and a clay-based engineered barrier in the context of deep underground disposal of high-level radioactive waste. [...]
- 4
- read
On the choice of stress–strain variables for unsaturated soils and its effect on plastic flow
D. Gallipoli, P. Grassi, S. Wheeler, A. Gens

Geomechanics for energy and the environment (2018). Vol. 15, pp. 3-9 (Preprint)

Abstract
The net stress plus suction and the average skeleton stress plus modified suction are two alternative sets of energetically consistent stress variables for modelling the hydro-mechanical behaviour of unsaturated soils. When used in conjunction with their work-conjugate strains, both sets of stress variables correctly calculate the first-order term of the hydro-mechanical work input into a soil element subjected to infinitesimal changes of deformation and water content. They therefore also correctly calculate the increment of internal energy along a given stress–strain path, that is the integral of the first-order term of the infinitesimal work input. This paper shows, however, that the above two sets of stress variables lead to different values of the second-order term of the hydro-mechanical work input. They are therefore no longer equivalent with respect to other aspects of material behaviour governed by the second-order work such as the flow rule of elasto-plastic models. The flow rule assumes the normality between plastic strains and equipotential surfaces defined in the conjugate stress–strain space. This normality is however lost when an elasto-plastic model originally formulated in terms of net stress plus suction is recast in terms of average skeleton stress plus modified suction (or vice versa) by means of standard mapping relationships between stress variables. To restore normality in both stress spaces, it is necessary to impose specific forms of elastic and plastic behaviour.
Abstract
The net stress plus suction and the average skeleton stress plus modified suction are two alternative sets of energetically consistent stress variables for modelling the hydro-mechanical [...]
- 4
- read
A new modelling approach for unsaturated soils using independent stress variables
D. Sheng, D. Fredlund, A. Gens

Canadian Geotechnical Journal (2008). Vol. 45 (4), pp. 511-534

Abstract
Although a number of constitutive models for unsaturated soils exist in the literature, some fundamental questions have not been fully answered. There are questions related to (i) the change of the yield stress with soil suction, (ii) modelling slurry soils, and (iii) the smooth transition between saturated and unsaturated soil states. This paper addresses these questions by proposing an alternative modelling approach. The paper first presents a volumetric model for unsaturated soils. This volumetric model is then used to derive the yield surface in the suction – mean stress space. Hysteresis associated with soil-water characteristic curves is then formulated in the same framework of elastoplasticity. It is shown that volume collapse during wetting and plastic shrinkage during initial drying are both direct results of a suction-dependent hardening law. The proposed model seems to be more flexible in modelling different types of unsaturated soils than most models in the literature. The model can be applied to soils that are dried or loaded from initially slurry conditions, for soils that have low to high air-entry values, and for compacted soils as well. R.M. Quigley Award 2009 (to authors of the best paper published in the Canadian Geotechnical Journal in the preceding year)
Abstract
Although a number of constitutive models for unsaturated soils exist in the literature, some fundamental questions have not been fully answered. There are questions related [...]
- 4
- read
Coupled thermo-hydro-mechanical analysis of engineered barriers for high level radioactive waste
A. Gens, S. Olivella

Chinese journal of rock mechanics and engineering (2006). Vol. 25 (4), pp. 670-680

Abstract
A general formulation for the performance of coupled thermo-hydro-mechanical (THM) analysis is presented. A multi-phase and multi-species approach has been adopted for the development of the formulation. The analysis considers a porous material with three phases (solid, liquid and gas) and three species (mineral, water and air). The formulation is presented in terms of governing equations, constitutive laws and equilibrium restrictions. An extensive programme of coupled THM analyses simulating the behaviour of the near field in a scheme for the underground disposal of high level radioactive waste is presented. The analyses are able to take into account the main interactions between the various processes that occur in the engineered barrier and immediately adjacent rock associated with heating and hydration phenomena. Examination of the results leads to a series of significant conclusions concerning the thermal, hydraulic and mechanical aspects of the problem.
Abstract
A general formulation for the performance of coupled thermo-hydro-mechanical (THM) analysis is presented. A multi-phase and multi-species approach has been adopted for the [...]
- 4
- read
Nonlocal plasticity modelling of strain localisation in stiff clays
M. Mánica, A. Gens, J. Vaunat, D. Ruiz

Computers and Geotechnics (2018). Vol. 103, pp. 138-150

Abstract
The paper addresses the numerical simulation of strain localisation in stiff clays that exhibit softening behaviour. An elastoplastic constitutive model developed to incorporate key features of stiff clay behaviour is described first. A non-local formulation is then introduced for the regularisation of the analysis of localisation. A series of analyses were conducted to explore relevant aspects of the numerical simulation of localisation. A 3D analysis was also performed to assess the suitability of the approach presented for 3D applications. Finally, application to the simulation of a laboratory test on Beaucaire marl results in an excellent reproduction of experimental observations.
Abstract
The paper addresses the numerical simulation of strain localisation in stiff clays that exhibit softening behaviour. An elastoplastic constitutive model developed to incorporate [...]
- 4
- read
Grading evolution and critical state in a discrete numerical model of Fontainebleau sand
M. Ciantia, M. Arroyo, C. O'Sullivan, A. Gens, T. Liu

Géotechnique (2019). Vol. 69 (1), pp. 1-15 (Preprint)

Abstract
Granular materials reach critical states upon shearing. The position and shape of a critical state line (CSL) in the compression plane are important for constitutive models, interpretation of in situ tests and liquefaction analyses. It is not fully clear how grain crushing may affect the identification and uniqueness of the CSL in granular soils. Discrete-element simulations are used here to establish the relation between breakage-induced grading evolution and the CSL position in the compression plane. An efficient model of particle breakage is applied to perform a large number of tests, in which grading evolution is continuously tracked using a grading index. Using both previous and new experimental results, the discrete-element model is calibrated and validated to represent Fontainebleau sand, a quartz sand. The results obtained show that, when breakage is present, the inclusion of a grading index in the description of critical states is advantageous. This can be simply done using the critical state plane (CSP) concept. A CSP is obtained for Fontainebleau sand.
Abstract
Granular materials reach critical states upon shearing. The position and shape of a critical state line (CSL) in the compression plane are important for constitutive models, [...]
- 4
- read
SDMT-based numerical analyses of deep excavation in soft soil
A. Marino, S. Amoroso, M. Arroyo, P. Monaco, A. Gens

Journal of Geotechnical and Geoenvironmental Engineering (2019). Vol. 145 (1), pp. 04018102-1/04018102-12

Abstract
The paper explores the application of conventional (DMT) and seismic (SDMT) dilatometer tests to an important case of deep excavation design. The work presents finite-element analyses simulating a deep excavation close to Barcelona (Spain). A thick layer of soft interbedded sandy and silty soils made characterization based on laboratory testing very difficult. SDMT offered an alternative for estimating the soil stiffness and its stress-strain dependency. Numerical results and high-quality monitoring data show quite close agreement for most phases of the construction process, supporting the use of seismic dilatometer tests in numerical analyses of deep excavations. The paper also indicates the importance of incorporating stiffness data at low strains. FE analyses involved some uncertainties derived from the presence of jet-grouting soil treatments. On this point, a parametric study illustrates the effects of different modeling approaches.
Abstract
The paper explores the application of conventional (DMT) and seismic (SDMT) dilatometer tests to an important case of deep excavation design. The work presents finite-element [...]
- 4
- read
Coupled Soil-Structure Interaction Modeling and Simulation of Landslide Protective Structures
B. Chandra, A. LARESE, P. Bucher, R. Wüchner

(2019). VIII International Conferenceon Computational Methods for Coupled Problems in Science and Engineering

Abstract
Within the past two decades, mass movements hazards involving fast and large soil deformation have increased significantly in frequency and magnitude due to their strong relation to climate changes and global warming. These phenomena often bring along rocks, debris, and heavy materials that can extensively damage and destroy the landscape and infrastructures, causing devastating economic loss, and often, human casualties. The risk of future disasters continues to escalate with the increase of real estate development in suburban areas, including mountainous regions. Further assessment and prediction on such disasters and their countermeasures are, therefore, in high economic demands. One of the most intuitive ways is to install protective structures in mountain slopes and valleys that can hold the materials brought by the moving landslides. While the current state of the art of landslide prediction using numerical methods has been mainly dominated by the development of advanced geomechanical models suited for different types of soil materials, e.g. multi-phase unsaturated soil model, this study focuses more on the interaction of such phenomena with the installed protective structures. Here, an implicit formulation of material point method (MPM) is implemented to model the landslides considering finite strain assumption. Furthermore, a staggered coupling scheme with traditional Finite Element Method (FEM) is proposed to simulate accurately and robustly the dynamic force and displacement coupling of soil-structure interaction (SSI). All developments of the method are implemented within the Kratos-Multiphysics framework and available under the BSD license (https://github.com/KratosMultiphysics/Kratos/wiki). In the future works, more adequate consideration of coupling scheme and material models considering damage and fracture will be investigated before conducting a real-scale landslide simulation.
Abstract
Within the past two decades, mass movements hazards involving fast and large soil deformation have increased significantly in frequency and magnitude due to their strong relation [...]
- 4
- read
Coupled effective stress analysis of insertion problems in geotechnics with the Particle Finite Element Method
L. Monforte, M. Arroyo, J. Carbonell, A. Gens

Computers and Geotechnics (2018). Vol. 101, pp. 114-129

Abstract
This paper describes a computational framework for the numerical analysis of quasi-static soil-structure insertion problems in water saturated media. The Particle Finite Element Method is used to solve the linear momentum and mass balance equations at large strains. Solid-fluid interaction is described by a simplified Biot formulation using pore pressure and skeleton displacements as basic field variables. The robustness and accuracy of the proposal is numerically demonstrated presenting results from two benchmark examples. The first one addresses the consolidation of a circular footing on a poroelastic soil. The second one is a parametric analysis of the cone penetration test (CPTu) in a material described by a Cam-clay hyperelastic model, in which the influence of permeability and contact roughness on test results is assessed.
Abstract
This paper describes a computational framework for the numerical analysis of quasi-static soil-structure insertion problems in water saturated media. The Particle Finite [...]
- 3
- read
Low‐order stabilized finite element for the full Biot formulation in soil mechanics at finite strain
L. Monforte, P. Navas, J. Carbonell, M. Arroyo, A. Gens

International Journal for Numerical and Analytical Methods in Geomechanics (2019). Vol. 43 (7), pp. 1488-1515

Abstract
This article presents a novel finite element formulation for the Biot equation using low‐order elements. Additionally, an extra degree of freedom is introduced to treat the volumetric locking steaming from the effective response of the medium; its balance equation is also stabilized. The accuracy of the proposed formulation is demonstrated by means of numerical analyses.
Abstract
This article presents a novel finite element formulation for the Biot equation using low‐order elements. Additionally, an extra degree of freedom is introduced to treat [...]
- 3
- read
Understanding and strain-engineering wrinkle networks in supported graphene through simulations
K. Zhang, M. Arroyo

Journal of the Mechanics and Physics of Solids (2014). Vol. 72, pp. 61-74 (Preprint)

Abstract
Wrinkle networks are ubiquitous buckle-induced delaminations in supported graphene, which locally modify the electronic structure and degrade device performance. Although the strong property-deformation coupling of graphene can be potentially harnessed by strain engineering, it has not been possible to precisely control the geometry of wrinkle networks. Through numerical simulations based on an atomistically informed continuum theory, we understand how strain anisotropy, adhesion and friction govern spontaneous wrinkling. We then propose a strategy to control the location of wrinkles through patterns of weaker adhesion. This strategy is deceptively simple, and can in fact fail in several ways, particularly under biaxial compression. However, within bounds set by the physics of wrinkling, it is possible to robustly create by strain a variety of wrinkle network geometries and junction configurations. Graphene is nearly unstrained in the planar regions bounded by wrinkles, highly curved along wrinkles, and highly stretched and curved at junctions, which can either locally attenuate or amplify the applied strain depending on their configuration. These mechanically self-assembled networks are stable under the pressure produced by an enclosed fluid and form continuous channels, opening the door to nano-fluidic applications.
Abstract
Wrinkle networks are ubiquitous buckle-induced delaminations in supported graphene, which locally modify the electronic structure and degrade device performance. Although [...]
- 3
- read
Hydraulic fracture and toughening of a brittle layer bonded to a hydrogel
A. Lucantonio, G. Noselli, X. Trepat, A. DeSimone, M. Arroyo

Physical review letters (2015). Vol. 115 (18), pp. 188105-1/188105-5

Abstract
Brittle materials propagate opening cracks under tension. When stress increases beyond a critical magnitude, then quasistatic crack propagation becomes unstable. In the presence of several precracks, a brittle material always propagates only the weakest crack, leading to catastrophic failure. Here, we show that all these features of brittle fracture are fundamentally modified when the material susceptible to cracking is bonded to a hydrogel, a common situation in biological tissues. In the presence of the hydrogel, the brittle material can fracture in compression and can hydraulically resist cracking in tension. Furthermore, the poroelastic coupling regularizes the crack dynamics and enhances material toughness by promoting multiple cracking.
Abstract
Brittle materials propagate opening cracks under tension. When stress increases beyond a critical magnitude, then quasistatic crack propagation becomes unstable. In the presence [...]
- 3
- read
Swimming Euglena respond to confinement with a behavioural change enabling effective crawling
G. Noselli, A. Beran, M. Arroyo, A. DeSimone

Nature physics (2019). Vol. 15, pp. 496-502 (Preprint)

Abstract
Some euglenids, a family of aquatic unicellular organisms, can develop highly concerted, large-amplitude peristaltic body deformations. This remarkable behaviour has been known for centuries. Yet, its function remains controversial, and is even viewed as a functionless ancestral vestige. Here, by examining swimming Euglena¿gracilis in environments of controlled crowding and geometry, we show that this behaviour is triggered by confinement. Under these conditions, it allows cells to switch from unviable flagellar swimming to a new and highly robust mode of fast crawling, which can deal with extreme geometric confinement and turn both frictional and hydraulic resistance into propulsive forces. To understand how a single cell can control such an adaptable and robust mode of locomotion, we developed a computational model of the motile apparatus of Euglena cells consisting of an active striated cell envelope. Our modelling shows that gait adaptability does not require specific mechanosensitive feedback but instead can be explained by the mechanical self-regulation of an elastic and extended motor system. Our study thus identifies a locomotory function and the operating principles of the adaptable peristaltic body deformation of Euglena cells.
Abstract
Some euglenids, a family of aquatic unicellular organisms, can develop highly concerted, large-amplitude peristaltic body deformations. This remarkable behaviour has been [...]
- 3
- read
Temperature effects on the hydraulic behaviour of an unsaturated clay
E. Romero, A. Gens, A. Lloret

Geotechnical and Geological Engineering (2001). Vol. 19 (3/4), pp. 311-332

Abstract
The influence of temperature on the hydraulic properties of unsaturated clays is of major concern in the design of engineered barriers in underground repositories for high-level radioactive waste disposal. This paper presents an experimental study centred on the investigation of the influence of temperature on soil hydraulic properties related to water retention and permeability. Laboratory tests were conducted on artificially prepared unsaturated fabrics obtained from a natural kaolinitic-illitic clay. Special attention is given to the testing procedures involving controlled suction and temperature oedometer cells and the application of the vapour equilibrium technique at high temperatures. Retention curves at different temperatures show that total suction tends to reduce with increasing temperatures at constant water content. Temperature influence on water permeability is more relevant at low matric suctions corresponding to bulk water preponderance (inter-aggregate zone). Below a degree of saturation of 75% no clear effect is detected. Experimental data show that temperature dependence on permeability at constant degree of saturation and constant void ratio is smaller than what could be expected from the thermal change in water viscosity. This behaviour suggests that phenomena such as porosity redistribution and thermo-chemical interactions, which alter clay fabric and pore fluid, can be relevant.
Abstract
The influence of temperature on the hydraulic properties of unsaturated clays is of major concern in the design of engineered barriers in underground repositories for [...]
- 3
- read
A constitutive model for crushed salt
S. Olivella, A. Gens

International Journal for Numerical and Analytical Methods in Geomechanics (2002). Vol. 26 (7), pp. 719-746

Abstract
A constitutive model for crushed salt is presented in this paper. A creep constitutive model is developed¿rst and compared with test results. The constitutive model presented here concentrates on creepdeformation because saline media behave basically in a ductile and time-dependent way. An idealizedgeometry is used as a common framework to obtain stress–strain macroscopic laws based on twodeformation mechanisms: ¿uid-assisted diffusional transfer creep and dislocation creep. The model is ableto predict strain rates that compare well with results from laboratory tests under isotropic and oedometricconditions. Macroscopic laws are written using a non-linear viscous approach, which incorporates also aviscoplastic component, based on critical state theory. The viscoplastic term is intended for non-creepdeformation mechanisms such as grain reorganization and crushing.
Abstract
A constitutive model for crushed salt is presented in this paper. A creep constitutive model is developed¿rst and compared with test results. The constitutive model [...]
- 3
- read
An elasto-plastic model for unsaturated soil incorporating the effects of suction and degree of saturation on mechanical behaviour
D. Gallipoli, A. Gens, A. Sharma, J. Vaunat

Géotechniques (2003). Vol. 53 (1), pp. 123-135

Abstract
The paper presents an elasto-plastic model for unsaturated soils that takes explicitly into account the mechanisms with which suction affects mechanical behaviour as well as their dependence on degree of saturation. The proposed model is formulated in terms of two constitutive variables directly related to these suction mechanisms: the average skeleton stress, which includes the average fluid pressure acting on the soil pores, and an additional scalar constitutive variable, ξ, related to the magnitude of the bonding effect exerted by meniscus water at the inter-particle contacts. The formulation of the model in terms of variables closely related to specific behaviour mechanisms leads to a remarkable unification of experimental results of tests carried out with different suctions. The analysis of experimental isotropic compression data strongly suggests that the quotient between the void ratio, e, of an unsaturated soil and the void ratio es, corresponding to the saturated state at the same average soil skeleton stress, is a unique function of the bonding effect due to water menisci at the inter-particle contacts. The same result is obtained when examining critical states at different suctions. Based on these observations, an elasto-plastic constitutive model is developed using a single yield surface the size of which is controlled by volumetric hardening. In spite of this simplicity, it is shown that the model reproduces correctly many important features of unsaturated soil behaviour. It is especially remarkable that, although only one yield surface is used in the formulation of the model, the irreversible behaviour in wetting–drying cycles is well captured. Because of the behaviour normalisation achieved by the model, the resulting constitutive law is economical in terms of the number of tests required for parameter determination.
Abstract
The paper presents an elasto-plastic model for unsaturated soils that takes explicitly into account the mechanisms with which suction affects mechanical behaviour as [...]
- 3
- read
Suction effects on a compacted clay under non-isothermal conditions
E. Romero, A. Gens, A. Lloret

Geotechnique (2003). Vol. 53 (1), pp. 65-81

Abstract
The paper presents the results of an experimental study on the effects of suction and temperature on the volumetric behaviour of an unsaturated soil. Statically compacted Boom clay samples have been used in the testing programme, which has been performed using an oedometer apparatus with simultaneous control of suction and temperature. Suctions up to 0·45 MPa and temperatures up to 80°C have been applied. Special measures have been taken to control and minimise the problems associated with phase changes and vapour migration at high temperatures. A comprehensive experimental programme has been carried out, including isothermal tests with control of vertical stress, suction and temperature, non-isothermal tests under constant suction, and isothermal swelling pressure tests. Testing samples at two compacted soil densities provides observations concerning a wide scope of behaviour ranging from collapse to swelling behaviour on wetting. Test results obtained at 80°C have been compared with those of tests performed at room temperature (22°C). Based on these comparisons, thermal effects on a variety of features of behaviour such as swelling potential, swelling pressure, collapsibility, shrinkage strains, compressibility, stress path dependence and degree of strain reversibility are presented and discussed. Although the basic behaviour is similar at high and low temperatures, various significant differences are identified concerning mainly swelling strains developed during wetting and compressibility with respect to loading. Swelling pressure test results indicate that the high-temperature samples yield at a lower stress than that observed in room-temperature samples, suggesting that the stress domain bounded by the main yield surface reduces as temperature increases—a behaviour feature shared with saturated soils.
Abstract
The paper presents the results of an experimental study on the effects of suction and temperature on the volumetric behaviour of an unsaturated soil. Statically compacted [...]
- 3
- read
Influence of rainfall on the deformation and stability of a slope in overconsolidated clays: a case study
E. Alonso, A. Gens, C. Delahaye

Hydrogeology journal (2003). Vol. 11 (1), pp. 174-192

Abstract
The behaviour of an instrumented unstable slope in a profile of weathered overconsolidated clay has been analysed. Available field investigation data and laboratory tests were integrated in a coupled hydromechanical model of the slope. Particular attention was given to the unsaturated soil conditions above the water table and to the influence of the rainfall record. Recorded pore-water pressures helped to identify the hydrogeological conditions of the slope. The coupled model was used to compute slope deformations and the variation of safety with time. Actual rainfall records were also integrated into the analysis. Comparison of measurements and calculations illustrate the nature of the slope instability and the complex relationships between mechanical and hydraulic factors.
Abstract
The behaviour of an instrumented unstable slope in a profile of weathered overconsolidated clay has been analysed. Available field investigation data and laboratory tests [...]
- 3
- read
Cone penetration tests in a virtual calibration chamber
M. Arroyo, J. Butlanska, A. Gens, F. Calvetti, M. Jamiolkowski

Géotechnique (2011). Vol. 61 (6), pp. 525-531

Abstract
A virtual calibration chamber was built using a threedimensional model based on the discrete-element method. The chamber was then filled with a scaled granular equivalent of Ticino sand, the material properties of which were selected by curve-fitting triaxial tests. Cone penetration tests were then performed under different initial densities and isotropic stresses. Penetration resistance in the virtual calibration chamber was affected by the same cone/chamber size effect that affects physical calibration chambers and was corrected accordingly. The corrected cone resistance obtained from the virtual calibration chamber cone penetration tests shows good quantitative agreement with correlations that summarise previous physical results.
Abstract
A virtual calibration chamber was built using a threedimensional model based on the discrete-element method. The chamber was then filled with a scaled granular equivalent [...]
- 3
- read
Tunnelling and swelling in triassic sulphate–bearing rocks: part I: case studies from Baden–Württemberg
I. Berdugo, E. Alonso, E. Romero, A. Gens

Epsilon (2009). Vol. 12, pp. 13-37

Abstract
Cases of swelling in tunnels excavated through Triassic sulphate-bearing rocks from the Gipskeuper and the Anhydritgruppe are presented and discussed in this series of papers in order to gain a better understanding of the expansive phenomena in these materials and to identify the most relevant ones. Part I deals with main features of swelling in tunnels and alternative supports designs for their control an mitigation, as well as with the phenomenology of swelling in tunnels from Baden-Württemberg (Germany) excavated through the Gipskeuper.
Abstract
Cases of swelling in tunnels excavated through Triassic sulphate-bearing rocks from the Gipskeuper and the Anhydritgruppe are presented and discussed in this series of papers [...]
- 3
- read
In situ behaviour of a stiff layered clay subject to thermal loading: Observations and interpretation
A. Gens, J. Vaunat, B. Garitte, Y. Wileveau

Geotechnique (2007). Vol. 57 (2), pp. 207-228

Abstract
The paper presents an interpretation of an in situ heating test carried out on Opalinus clay in the Mont Terri underground laboratory. Opalinus clay is a stiff, strongly bedded, Mesozoic clay of marine origin. When subjected to thermal loading, saturated stiff clays exhibit a strong pore pressure response that significantly affects the hydraulic and mechanical behaviour of the material. The observations gathered in the in situ test have provided an opportunity to examine the integrated thermo-hydro-mechanical (THM) response of this sedimentary clay. Coupled THM numerical analyses have been carried out to provide a structured framework for interpretation, and to enhance understanding of THM clay behaviour. Numerical analyses have been based on a coupled theoretical formulation that incorporates a constitutive law especially developed for this type of material. The law includes degradation of bonding by damage. By performing three-dimensional computations, it has been possible to incorporate anisotropy of material parameters and of in situ stresses. The 3D simulation has proved able to furnish a satisfactory representation of the development of the in situ test and of the main observed patterns of behaviour. A sensitivity analysis has also been carried out to examine the potential effect of various key or uncertain parameters. The critical examination of test observations and the results of the numerical analyses have allowed the classification, by differing degrees of significance, of the various coupled phenomena present in the problem
Abstract
The paper presents an interpretation of an in situ heating test carried out on Opalinus clay in the Mont Terri underground laboratory. Opalinus clay is a stiff, strongly bedded, [...]
- 3
- read
Coupled thermal-hydrological-mechanical analyses of the Yucca Mountain Drift Scale Test-Comparison of field measurements to predictions of four different numerical models
J. Rutqvist, D. Barr, R. Datta, A. Gens, A. Millard, S. Olivella, C. Tsang, Y. Tsang

International Journal of Rock Mechanics and Mining Sciences (2005). Vol. 42 (5-6), pp. 680-697

Abstract
The Yucca Mountain Drift Scale Test (DST) is a multiyear, large-scale underground heating test designed to study coupled thermal–hydrological–mechanical–chemical behavior in unsaturated fractured and welded tuff. As part of the international cooperative code-comparison project DEvelopment of COupled models and their VALidation against EXperiments, four research teams used four different numerical models to simulate and predict coupled thermal–hydrological–mechanical (THM) processes at the DST. The simulated processes included heat transfer, liquid and vapor water movements, rock-mass stress and displacement, and stress-induced changes in fracture permeability. Model predictions were evaluated by comparison to measurements of temperature, water saturation, displacement, and air permeability. The generally good agreement between simulated and measured THM data shows that adopted continuum model approaches are adequate for simulating relevant coupled THM processes at the DST. Moreover, thermal-mechanically induced rock-mass deformations were reasonably well predicted using elastic models, although some individual displacements appeared to be better captured using an elasto-plastic model. It is concluded that fracture closure/opening caused by change in normal stress across fractures is the dominant mechanism for thermal-stress-induced changes in intrinsic fracture permeability at the DST, whereas fracture shear dilation appears to be less significant. This indicates that such changes in intrinsic permeability at the DST, which are within one order of magnitude, are likely to be mostly reversible.
Abstract
The Yucca Mountain Drift Scale Test (DST) is a multiyear, large-scale underground heating test designed to study coupled thermal–hydrological–mechanical–chemical [...]
- 3
- read
Finite element formulation and algorithms for unsaturated soils. Part I: theory
D. Sheng, S. Sloan, A. Gens, D. Smith

International Journal for Numerical and Analytical Methods in Geomechanics (2003). Vol. 27 (9), pp. 745-765

Abstract
This paper presents a complete finite-element treatment for unsaturated soil problems. A new formulation of general constitutive equations for unsaturated soils is first presented. In the incremental stress–strain equations, the suction or the pore water pressure is treated as a strain variable instead of a stress variable. The global governing equations are derived in terms of displacement and pore water pressure. The discretized governing equations are then solved using an adaptive time-stepping scheme which automatically adjusts the time-step size so that the integration error in the displacements and pore pressures lies close to a specified tolerance. The non-linearity caused by suction-dependent plastic yielding, suction-dependent degree of saturation, and saturation-dependent permeability is treated in a similar way to the elastoplasticity. An explicit stress integration scheme is used to solve the constitutive stress–strain equations at the Gauss point level. The elastoplastic stiffness matrix in the Euler solution is evaluated using the suction as well as the stresses and hardening parameters at the start of the subincrement, while the elastoplastic matrix in the modified Euler solution is evaluated using the suction at the end of the subincrement. In addition, when applying subincrementation, the same rate is applied to all strain components including the suction
Abstract
This paper presents a complete finite-element treatment for unsaturated soil problems. A new formulation of general constitutive equations for unsaturated soils is first presented. [...]
- 3
- read
Chemical impact on the hydro-mechanical behaviour of high-density Febex bentonite
E. Castellanos, M. Villar, E. Romero, A. Lloret, A. Gens

Physics and Chemistry of the Earth (2008). Vol. 33 (S1), pp. S516-S526

Abstract
The effect of the salinity of the saturating fluid on the hydro-mechanical properties of the FEBEX compacted bentonite was investigated by means of swelling, compressibility and permeability tests in which deionised water and solutions of different concentrations and compositions were used as saturating fluids. The solutions were chosen to simulate natural and extreme conditions in a high-level radioactive waste repository excavated in crystalline or clay host rocks. The swelling capacity of the bentonite decreases with the increase in salinity of the pore water, although this difference becomes less patent for high vertical loads and high densities and when the salinity of the solution is very low. The samples saturated with solutions containing high concentration of ions are also less deformable and consolidate more rapidly than the samples saturated with low-salinity solutions. The hydraulic conductivity of the highly compacted saturated FEBEX bentonite increases when high-salinity permeants are used, especially for low densities and when the stress level is low. The influence of the composition of the solution on the hydro-mechanical properties of the bentonite was also checked.
Abstract
The effect of the salinity of the saturating fluid on the hydro-mechanical properties of the FEBEX compacted bentonite was investigated by means of swelling, compressibility and [...]
- 3
- read
Aznalcóllar dam failure. Part 3: dynamics of the motion
E. Alonso, A. Gens

Géotechniques (2006). Vol. 56 (3), pp. 203-210

Abstract
The motion of the Aznalcóllar dam slide, after the initiation of the failure, is examined in the paper. The moving mass remained essentially rigid, and Newton's second law provides the basic equation to determine the resulting dam displacement, velocity and acceleration. Resisting forces have been derived from a previous analysis of the conditions leading to failure. Pore water pressures induced by the forward motion of the dam are approximated as an undrained loading of the clay. Driving forces and their evolution in time derive from the liquefaction of tailings and the condition of constant volume of liquefied tailings pushing the moving dam forward. The stable ‘cliff’ left by the motion inside the tailings lagoon supports this hypothesis. The model is able to reproduce closely the distance travelled by the dam. It shows a low sensitivity with respect to reasonable changes of the main parameters. The model computes that the slide motion lasted about 15 s, and that the maximum acceleration experienced by the dam was 0·14g.
Abstract
The motion of the Aznalcóllar dam slide, after the initiation of the failure, is examined in the paper. The moving mass remained essentially rigid, and Newton's [...]
- 3
- read
A review of expansive phenomena in Wagenburg North Tunnel
I. Berdugo, E. Alonso, A. Gens, M. Albis

Revista de la academia Colombiana de Ciencias Exactas, Físicas y Naturales (2009). Vol. 31 (129), pp. 455-469

Abstract
The paper deals on tunnelling and swelling in anhydritic-gypsiferous claystones. The geology of the Gipskeuper in Baden-Württemberg (Germany) and the phenomenology of expansions in Wagenburg North tunnel are described. Consistent swelling triggering events, mechanisms and exhaustion causes were identified using a thermo-hydro-chemo-mechanical theoretical analysis. It is suggested that long-term swelling in tunnels excavated through anhydritic-gypsiferous claystones is a result of solvent-way gypsum crystal growth due to ventilation induced groundwater evaporation and rock drying; an opposite concept to the usual consequences of drying in argillaceous materials, which causes shrinkage strains.
Abstract
The paper deals on tunnelling and swelling in anhydritic-gypsiferous claystones. The geology of the Gipskeuper in Baden-Württemberg (Germany) and the phenomenology of [...]
- 3
- read
Artificial ground freezing of a volcanic ash: laboratory tests and modelling
F. Casini, A. Gens, S. Olivella, G. Viggiani

Environmental geotechnics (2016). Vol. 3 (3), pp. 1-14 (Preprint)

Abstract
The use of artificial ground freezing (AGF) to form earth support systems has had applications worldwide. These cover a variety of construction problems, including the formation of frozen earth walls to support deep excavations, structural underpinning for foundation improvement and temporary control of ground water in construction processes. On one hand, the main advantage of AGF as a temporary support system in comparison to other support methods, such as those based on injections of chemical or cement grout into the soil, is the low impact on the surrounding environment as the refrigerating medium required to obtain AGF is circulated in pipes and exhausted in the atmosphere or re-circulated without contamination of the ground water. On the other hand, the available methods may vary significantly in their sustainability and complexity in terms of times and costs required for their installation and maintenance. The ability to predict the effects induced by AGF on granular materials is therefore crucial to assessing construction time and cost and to optimising the method. In this work, the thermo-hydro-mechanical processes induced by artificial freezing of a soil body are studied using a constitutive model that encompasses frozen and unfrozen behaviour within a unified effective-stress-based framework. It makes use of a combination of ice pressure, liquid water pressure and total stress as state variables. The model is validated and calibrated using the results of a series of laboratory tests on natural samples of a volcanic ash (Pozzolana) retrieved during construction of Napoli underground, where the technique of AGF was used extensively to stabilise temporarily the ground and control the ground water.
Abstract
The use of artificial ground freezing (AGF) to form earth support systems has had applications worldwide. These cover a variety of construction problems, including the [...]
- 3
- read
Numerical analysis of the hydromechanical response of Callovo-Oxfordian claystone to deep excavations
D. Seyedi, A. Gens

Computers and Geotechnics (2017). Vol. 85, pp. 275-276 (Preprint)

Abstract
Deep geological disposal is considered as one of the promising options for the long-term management of the High-Level (HL) and Intermediate-Level Long-Lived (IL-LL) radioactive waste. Different argillaceous formations are studied in different countries for this purpose, such as, Opalinus clay in Switzerland, Boom clay in Belgium and Callovo-Oxfordian claystone in France.
Abstract
Deep geological disposal is considered as one of the promising options for the long-term management of the High-Level (HL) and Intermediate-Level Long-Lived (IL-LL) radioactive [...]
- 3
- read
An approach to enhance efficiency of DEM modelling of soils with crushable grains
M. Ciantia, M. Arroyo, F. Calvetti, A. Gens

Géotechnique (2015). Vol. 65 (2), pp. 91-110 (Preprint)

Abstract
In this study oedometric compression tests of hydrocarbon coke, Fontainebleau sand and silica sand are simulated in three dimensions using breakable particles. The method adapts a rigorous breakage criterion for elasto-brittle spheres to represent failure of grains isolated between platens or within granular masses. The breakage criterion allows for the effect of particle bulk and contact properties to be treated separately. A discrete fragmentation multigenerational approach is applied as a spawning procedure. The number of particles quickly increases during the simulation, but is kept manageable by systematic fine exclusion and upscaling. Fine exclusion leads to mass losses between generations, but that loss is accounted for outside the mechanical model. Sensitivity analysis shows that it is enough to keep 53% of the crushed particle mass within the mechanical model to correctly reproduce experimental macroscopic behaviour. Practical upscaling rules are proposed for (a) contact stiffness, (b) breakage criteria and (c) grain size distribution, and validated simulating the same test, reducing by half the initial number of particles. The results are promising as both the mechanical and grading evolution are well captured with two orders of magnitude savings in computing efficiency.
Abstract
In this study oedometric compression tests of hydrocarbon coke, Fontainebleau sand and silica sand are simulated in three dimensions using breakable particles. The method [...]
- 3
- read
Interpretation of unsaturated soil behaviour in the stress-saturation space. II: Constitutive relationships and validations
A. Zhou, D. Sloan, S. Sloan, A. Gens

Computers and Geotechnics (2012). Vol. 43, pp. 111-123

Abstract
Based on the equations for volume change and saturation variation proposed in the companion paper [37], an alternative constitutive framework is presented for interpreting coupled hydro-mechanical behaviour for unsaturated soils. In this new framework, all constitutive laws are built in the space of stress vs. degree of saturation. Suction is not involved explicitly in the constitutive model for unsaturated soils. The loading-collapse yield surface is derived based on the proposed volume change equation in the plane of the effective degree of saturation and the Bishop effective stress. The proposed volume change equation and the corresponding yield surface are generalised to three-dimensional stress states by incorporating with the Modified Cam-clay model, following the same procedure introduced in the Sheng–Fredlund–Gens (SFG) model. The basic properties and performance of the proposed constitutive model are then illustrated through numerical examples with various drying/wetting/loading paths. Finally, the proposed model is validated against a variety of experimental data including drained and undrained tests, isotropic and triaxial tests and reconstituted and compacted soils.
Abstract
Based on the equations for volume change and saturation variation proposed in the companion paper [37], an alternative constitutive framework is presented for interpreting [...]
- 3
- read
Clays in natural and engineered barriers for nuclear waste disposal
A. Gens

Geomechanics for energy and the environment (2019). Vol. 17, pp. 1-2

Abstract
Argillaceous rocks and expansive clays play a key role in many scenarios of the deep geological disposal of nuclear waste.
- 3
- read
Shear strength of rock joints influenced by compacted infill
B. Indraratna, W. Premadasa, E. Brown, A. Gens, A. Heitor

International Journal of Rock Mechanics and Mining Sciences (2014). Vol. 70, pp. 296-307

Abstract
Discontinuities such as fault planes, joints and bedding planes in a rock mass may be filled with different types of fine-grained material that are either transported or accumulated as gouge due to weathering or joint shearing. Previous laboratory studies have mainly examined the role of saturated infill that exhibits the minimum shear strength. However, in practice, the infill materials are often partially saturated generating matric suction within the joint that can contribute to increased shear strength. To the authors' knowledge this is the first study to examine the influence of compacted (unsaturated) infill on the joint shear strength. A series of laboratory triaxial tests on idealised model joints and imprinted natural joint profiles was carried out, with constant water contents of the infill being maintained. From the laboratory results, it is observed that the peak shear strength of infilled joints increased with the decrease of degree of saturation from 85% to 35% for both idealised joints and replicated natural joints. Based on the laboratory observations an empirical model for describing the infilled joint shear strength was developed.
Abstract
Discontinuities such as fault planes, joints and bedding planes in a rock mass may be filled with different types of fine-grained material that are either transported or accumulated [...]
- 3
- read
Numerical simulation of the undrained stability of slopes in anisotropic fine-grained soils
S. Conesa, M. Mánica, A. Gens, Y. Huang

Geomechanics and Geoengineering (2019). Vol. 14 (1), pp. 18-29

Abstract
The undrained stability of slopes in anisotropic fine-grained soils is studied in this paper using the finite element method (FEM). A constitutive model is presented, able to account for the observed variation of undrained strength with loading direction. The model is able to encompass the different strength distributions observed in normally, slightly overconsolidated and heavily overconsolidated soils. A series of stability analyses have been performed to explore the effect of the type of undrained strength anisotropy on the stability and failure mechanisms of slopes of different inclinations. In addition, a real case study of the failure of an underwater slope is analysed with the numerical approach presented. It suggests that, by considering undrained strength anisotropy, the failure can be satisfactorily explained.
Abstract
The undrained stability of slopes in anisotropic fine-grained soils is studied in this paper using the finite element method (FEM). A constitutive model is presented, able [...]
- 3
- read
DEM modelling of cone penetration tests in a double-porosity crushable granular material
M. Ciantia, M. Arroyo, J. Butlanska, A. Gens

Computers and Geotechnics (2016). Vol. 73, pp. 109-127 (Preprint)

Abstract
A three-dimensional discrete element model is used to investigate the effect of grain crushing on the tip resistance measured by cone penetration tests (CPT) in calibration chambers. To do that a discrete analogue of pumice sand, a very crushable microporous granular material, is created. The particles of the discrete model are endowed with size-dependent internal porosity and crushing resistance. A simpli- fied Hertz–Mindlin elasto-frictional model is used for contact interaction. The model has 6 material parameters that are calibrated using one oedometer test and analogies with similar geomaterials. The calibration is validated reproducing other element tests. To fill a calibration chamber capable of containing a realistic sized CPT the discrete analogue is up-scaled by a factor of 25. CPT is then performed at two different densities and three different confinement pressures. Cone tip resistance in the crushable material is practically insensitive to initial density, as had been observed in previous physical experiments. The same CPT series is repeated but now particle crushing is disabled. The ratios of cone tip resistance between the two types of simulation are in good agreement with previous experimental comparisons of hard and crushable soils. Microscale exploration of the models indicates that crushing disrupts the buttressing effect of chamber walls on the cone. DEM modelling of cone penetration tests in a double-porosity crushable granular material.
Abstract
A three-dimensional discrete element model is used to investigate the effect of grain crushing on the tip resistance measured by cone penetration tests (CPT) in calibration [...]
- 3
- read
Anisotropic behaviour of compacted clayey silt subjected to hydromechanical paths
C. Buenfil, E. Romero, A. Lloret, A. Gens

E2S Web of Conferences (2016). Vol. 9, pp. 1-6

Abstract
Compaction induces anisotropy on soil deformational response due to preferential straining associated with the fabrication process. An experimental insight into the stress-strain response of Barcelona clayey silt is provided here. The material was statically compacted at low dry density to induce high collapsibility upon wetting (dry density 1.48 Mg/m3, water content 12%). Two types of controlled-suction tests were carried out: a) constant suction radial paths on as-compacted samples following different stress ratios (deviator stress / mean net stress: q/p Compaction induces anisotropy on soil deformational response due to preferential straining associated with the fabrication process. An experimental insight into the stress-strain response of Barcelona clayey silt is provided here. The material was statically compacted at low dry density to induce high collapsibility upon wetting (dry density 1.48 Mg/m3, water content 12%). Two types of controlled-suction tests were carried out: a) constant suction radial paths on as-compacted samples following different stress ratios (deviator stress / mean net stress: q/p¿, including isotropic and K0 stress paths; and b) the same type of radial stress paths but performed after saturation under low confining stress. These paths were intended to define the as-compacted and saturated yield surfaces. The experimental data on as-compacted state is satisfactorily interpreted adopting an anisotropic yield surface with an inclination linked to the compaction under oedometer conditions. Development of shear strain was observed during isotropic loading of the compacted samples. This anisotropy that the soil exhibits at the end of the compaction vanishes after collapse by saturation and as plastic volumetric straining develops
Abstract
Compaction induces anisotropy on soil deformational response due to preferential straining associated with the fabrication process. An experimental insight into the stress-strain [...]
- 3
- read
Hydraulic conductivity from piezocone on-the-fly: a numerical evaluation
L. Monforte, M. Arroyo, A. Gens, J. Carbonell

Géotechnique Letters (2018). Vol. 8 (4), pp. 268-277

Abstract
Permeability is important in many geotechnical applications. The current (cone penetration test that gathers piezometer data (CPTu)) practice to obtain permeability values relies on dissipation tests, which are frequently slow and only linked to permeability through compressibility measures. On-the-fly methods offer an alternative approach in which permeability is directly linked to CPTu penetration measurements. Several on-the-fly methods have been proposed and their applicability and relative advantages are not fully clear. Numerical effective stress simulation of CPTu testing is used here to explore in a simplified but realistic setting the relative merits of different on-the-fly methods. It is found that for partly drained materials, the original simpler relation between cone metrics and normalised permeability works reasonably well. A continuous generalisation of Elsworth and Lee method to the full permeability range is proposed, noting the connection to the backbone normalised pore-pressure curve that describes the partly drained transition of cone penetration. The importance of an undrained limit beyond which the method produces large errors is emphasised.
Abstract
Permeability is important in many geotechnical applications. The current (cone penetration test that gathers piezometer data (CPTu)) practice to obtain permeability values [...]
- 2
- read
Charting molecular free-energy landscapes with an atlas of collective variables
B. Hashemian, D. Millán, M. Arroyo

Journal of chemical physics (2016). Vol. 145 (17), pp. 1-33 (Preprint)

Abstract
Collective variables (CVs) are a fundamental tool to understand molecular flexibility, to compute free energy landscapes, and to enhance sampling in molecular dynamics simulations. However, identifying suitable CVs is challenging, and is increasingly addressed with systematic data-driven manifold learning techniques. Here, we provide a flexible framework to model molecular systems in terms of a collection of locally valid and partially overlapping CVs: an atlas of CVs. The specific motivation for such a framework is to enhance the applicability and robustness of CVs based on manifold learning methods, which fail in the presence of periodicities in the underlying conformational manifold. More generally, using an atlas of CVs rather than a single chart may help us better describe different regions of conformational space. We develop the statistical mechanics foundation for our multi-chart description and propose an algorithmic implementation. The resulting atlas of data-based CVs are then used to enhance sampling and compute free energy surfaces in two model systems, alanine dipeptide and ß-D-glucopyranose, whose conformational manifolds have toroidal and spherical topologies.
Abstract
Collective variables (CVs) are a fundamental tool to understand molecular flexibility, to compute free energy landscapes, and to enhance sampling in molecular dynamics simulations. [...]
- 2
- read
Numerical analysis of nonlinear large-strain consolidation and filling
A. Huerta, A. Rodríguez-Ferran

Computers and Structures (1992). Vol. 44 (1-2), pp. 357-365

Abstract
Finite strain consolidation and filling of soft sediments at high water level is a challenging problem because of its highly non-linear physical and mathematical aspects. Several numerical schemes designed for this problem are presented as well as simple numerical improvements for a better handling of the extremely high variations of the material properties with depth. The numerical algorithms developed are robust and verify convergence of the iterative schemes instead of the more classical approaches based on choosing time increments ‘sufficiently’ small and assuming convergence at every step. A set of computer programs has been developed to predict magnitude and rate of large-strain self-weight one-dimensional and pseudo bi-dimensional (i.e. one-dimensional deformation, bi-dimensional flux) consolidation during and after deposition, that is, coupling filling and consolidation phenomena. The actual life of the deposit can be numerically simulated combining filling periods and quiescent periods where surcharges (or capping) can exist. Consequently, they are a basic technique for the design of disposal ponds.
Abstract
Finite strain consolidation and filling of soft sediments at high water level is a challenging problem because of its highly non-linear physical and mathematical aspects. [...]
- 2
- read
Sticking and sliding of lipid bilayers on deformable substrates
L. Stubbington, M. Arroyo, M. Staykova

Soft Matter (2017). Vol. 13 (1), pp. 181-186

Abstract
We examine here the properties of lipid bilayers coupled to deformable substrates. We show that by changing the extent of the substrate hydrophilicity, we can control the membrane–substrate coupling and the response of the bilayer to strain deformation. Our results demonstrate that lipid bilayers coupled to flexible substrates can easily accommodate large strains, form stable protrusions and open reversibly pores. These properties, which differ significantly from those of free standing membranes, can extend the applications of the current lipid technologies. Moreover, such systems better capture the mechanical architecture of the cell interface and can provide insights into the capacity of cells to reshape and respond to mechanical perturbations.
Abstract
We examine here the properties of lipid bilayers coupled to deformable substrates. We show that by changing the extent of the substrate hydrophilicity, we can control the [...]
- 2
- read
Stability of anchored sheet wall in cohesive-frictional soils by FE limit analysis
J. Muñoz, A. Lyamin, A. Huerta

Int. J. Numer. Anal. Meth. Geomech. (2013). Vol. 37 (9), pp. 1213-1230 (Preprint)

Abstract
This study extends the limit analysis techniques used for the computation of strict bounds of the load factors in solids to stability problems with interfaces, anchors and joints. The cases considered include the pull-out capacity of multibelled anchors and the stability of retaining walls for multiple conditions at the anchor/soil and wall/soil interfaces. Three types of wall supports are examined: free standing wall, simply supported wall and anchored wall. The results obtained are compared against available experimental and numerical data. The conclusion drawn confirms the validity of numerical limit analysis for the computation of accurate bounds on limit loads and capturing failure modes of structures with multiple inclusions of complex interface and support conditions.
Abstract
This study extends the limit analysis techniques used for the computation of strict bounds of the load factors in solids to stability problems with interfaces, anchors and [...]
- 2
- read
Analysis of temporal and spatial variability of water balance components in a Mediterranean river basin: the Spanish part of the Duero basin.
D. Vicente, L. Rodríguez-Sinobas, F. Salazar, L. Garrote

Geophysical Research Abstracts (2019). Vol. 21, p.1

Abstract
Water balances have been identified as an effective tool for assessing the amount of water and its availability in a region. In particular, the System of Environmental-Economic Accounting for Water (SEEA-W) has emerged as one of the most complete methodologies to undertake this action. Despite the great effort made to offer a common methodology for elaborating the SEEA-W tables, there are multiple aspects that prevent its standardization in a generalized way. This leads both to multiple approaches in the realization of water balances and to the introduction of high uncertainty in the accounts obtained.The data series variability, both temporal and spatial, is one of the factors that can introduce large uncertainty into the water balances if they are not correctly evaluated. This aspect has not yet been specifically studied, and most of the case studies in the literature only provide the water balance values for a short period (usually a natural or hydrological year) and for a specific basin. In the case of having data corresponding to several years, average values are typically used to elaborate the calculations. In the present study, the SEEA-W methodology was applied to the Spanish part of Duero river basin. Each component of the water asset accounts was calculated using simulated data from three models: SIMPA (rainfall-runoff model), ASTER (snow-related processes model) and SIMGES (water allocation and management model). These models were developed and calibrated by different Spanish entities. Then, the uncertainty associated with the temporal and spatial irregularity of the data series was also estimated.The Duero basin is located in a semi-arid Mediterranean region, where hydrological processes are affected by high intra- and inter-annual variability. To analyse this issue both monthly and annual resolutions were used. The first allowed identifying a significant intra-annual variability. The second was analysed using a period of 26 years, from 1980 to 2006. The results show a high variability for certain hydrological components which can lead to a great degree of uncertainty. In addition, each hydrological year was classified as dry, average or wet and water balances were calculated under the same classification. This approach would improve the estimation of water resources including the prediction of future climate changes scenarios.Regarding the spatial variability, the water resources of the basin, like many of the large Mediterranean rivers, are not evenly distributed and showed large differences in hydrological processes. These differences are caused by climatic and geomorphological differences (the area comprises an extensive central plateau with a peripheral mountain arch). In addition, the analysis considers the different human activities coexisting within the basin and the heterogeneity of their spatial distribution. The water balances split into a more disaggregated territorial units could help to detect the areas with both positive and negative balances and improve the water resources management in the whole basin.
Abstract
Water balances have been identified as an effective tool for assessing the amount of water and its availability in a region. In particular, the System of Environmental-Economic [...]
- 2
- read
Parameter and variance estimation in geotechnical backanalysis using prior information
A. LEDESMA, A. Gens, E. Alonso

International Journal for Numerical and Analytical Methods in Geomechanics (1996). Vol. 20 (2), pp. 119-141

Abstract
A probabilistic framework to perform inverse analysis of geotechnical problems is presented. The formulation allows the incorporation of existing prior information on the parameters in a consistent way. The method is based on the maximum likelihood approach that allows a straightforward introduction of the error structure of field measurements and prior information. The difficulty of ascribing definite values to the uncertainties associated with the various types of observations is overcome by including the corresponding variances in the set of parameters to be identified. The inverse analysis results in a minimization problem that is solved by coupling the optimization technique to the finite element method. Two examples are presented to illustrate the performance of the method. The first one corresponds to a synthetic case simulating the excavation of a tunnel. Young's modulus, K0 value and measurements variances are identified. The second case concerns the excavation of a large underground cavern in which again Young's modulus and K0 are identified. It is shown that introduction of prior information permits the estimation of parameters more consistent with all available informations that include not only monitored displacements but also results from in situ tests carried out during the site investigation stage.
Abstract
A probabilistic framework to perform inverse analysis of geotechnical problems is presented. The formulation allows the incorporation of existing prior information on the [...]
- 2
- read
Estimation of parameters in geotechnical backanalysis. I- Maximum likehood approach
A. LEDESMA, A. Gens, E. Alonso

Computers and Geotechnics (1996). Vol. 18 (2), pp. 1-27

Abstract
The estimation of soil and rock parameters based on field instrumentation data is a common procedure in geomechanics. The use of system identification and optimization techniques allows the performance of this type of analyses in a more rational and objective manner. In this paper a probabilistic formulation for the backanalysis problem is presented. The procedure described involves the evaluation of the measurement covariance matrices, which are derived for some geotechnical instruments used in field instrumentation. The algorithm used to solve the mathematical problem of optimization is also presented, as well as its coupling to a finite element code. The algorithm requires the computation of the sensitivity matrix, which can be evaluated “exactly” in terms of the finite element method. Finally, a synthetic example, based on the excavation of a tunnel, is presented in which the elastic modulus E and the K0 parameter of the material are identified from measured displacements. The effect of the number of measurements and their error structure is also discussed.
Abstract
The estimation of soil and rock parameters based on field instrumentation data is a common procedure in geomechanics. The use of system identification and optimization [...]
- 2
- read
Analysis of a full scale "in situ" test simulating repository conditions
A. Gens, A. García-Molina, S. Olivella, E. Alonso, F. Huertas

International Journal for Numerical and Analytical Methods in Geomechanics (1998). Vol. 22 (7), pp. 515-548

Abstract
Coupled thermo‐hydro‐mechanical (THM) analyses have been used to examine the interacting phenomena associated with the simultaneous heating and hydration of an engineered bentonite barrier placed in a drift excavated in granite. The specific problem studied is an in situ test being carried out in the underground laboratory at Grimsel (Switzerland). After describing the test and the theoretical formulation, the results of a coupled THM analysis using the best parameter estimation currently available are presented and discussed. The effect of various features of analysis are explored by means of additional analyses in which each of those features are varied, one at the time. Finally, sensitivity analyses have been carried out to examine some critical aspects of the in situ test design. Performance of coupled THM analyses has led to a better understanding of the various inter‐related phenomena occurring during heating and hydration of the engineered clay barrier.
Abstract
Coupled thermo‐hydro‐mechanical (THM) analyses have been used to examine the interacting phenomena associated with the simultaneous heating and hydration of an engineered [...]
- 2
- read
Porosity variations in saline media caused by temperature gradients coupled to multiphase flow and dissolution/precipitation
S. Olivella, J. Carrera, A. Gens, E. Alonso

Transport in Porous Media (1996). Vol. 25 (1), pp. 1-25

Abstract
We present a theoretical-numerical investigation of porosity variations induced by temperature gradients in unsaturated saline media. It is known that temperature variations cause humidity variations which lead to liquid flow towards and vapour flow away from the hot source. When this phenomenon occurs in saline media, the liquid is salt saturated brine, so that evaporation causes salt precipitation and an ensuing porosity reduction. Condensation of water causes salt dissolution and porosity increase. This process may be important in the case of heat generating waste because it suggests that selfsealing may take place near the waste. On the other hand, salt mass balance will lead to porosity increases in other zones.
Abstract
We present a theoretical-numerical investigation of porosity variations induced by temperature gradients in unsaturated saline media. It is known that temperature variations [...]
- 2
- read
Evaluation of safety factors in discontinuous rock
E. Alonso, I. Carol, C. Delahaye, A. Gens, P. Prat

International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts (1996). Vol. 33 (5), pp. 513-537

Abstract
Safety factors for kinematically admissible failure mechanisms in jointed rock masses have been defined with linear and nonlinear failure criteria for rock discontinuities. Data required to compute these safety factors are obtained by means of two finite element anlayses of the effects of selfweight and external (structural) loading, respectively. Both types of analysis are closely linked since they share a common geometry. Joint elements are used to simulate the behaviour of rock discontinuities. If kinematically admissible mechanisms are possible under field conditions, the finite element mesh should also allow them to develop. Different aspects of the methodology have been illustrated through the safety evaluation of a 150 m high arch dam and its foundation in fractured cretaceous limestone. Special attention has been paid to the modelling of a realistic geometry including three-dimensional rock blocks and discontinuities. The paper discusses the effect of initial state of stress, the evolution of safety as the external load increases and the relation between the defined safety factors. It also provides practical guidelines for conducting this type of analysis in complex situations.
Abstract
Safety factors for kinematically admissible failure mechanisms in jointed rock masses have been defined with linear and nonlinear failure criteria for rock discontinuities. [...]
- 2
- read
Vapour transport in low permeability unsaturated soils with capillary effects
S. Olivella, A. Gens

Transport in Porous Media (2000). Vol. 40 (2), pp. 219-241

Abstract
A discussion of water phase change in unsaturated soils that develop capillary effects is first carried out in the paper. A distinction between the GR (geothermal reservoir) and the NUS (nonisothermal unsaturated soil) approaches is performed. Several aspects concerning advective and nonadvective fluxes of vapour are described secondly and some relationships concerning the case of mass motion in a closed system subjected to temperature gradients derived. Since the structure of unsaturated clays changes with moisture content, in order to correctly simulate the coupled phenomena induced by temperature gradients a model for intrinsic permeability as a function of humidity is required. A preliminary version of the model is presented and applied to interpret a laboratory test by means of a numerical simulation using CODE BRIGHT
Abstract
A discussion of water phase change in unsaturated soils that develop capillary effects is first carried out in the paper. A distinction between the GR (geothermal reservoir) [...]
- 2
- read
A double generalized plasticity model for expansive materials
M. Sánchez, A. Gens, L. Guimarães, S. Olivella

International Journal for Numerical and Analytical Methods in Geomechanics (2005). Vol. 29 (8), pp. 751-787

Abstract
The constitutive model presented in this work is built on a conceptual approach for unsaturated expansive soils in which the fundamental characteristic is the explicit consideration of two pore levels. The distinction between the macro- and microstructure provides the opportunity to take into account the dominant phenomena that affect the behaviour of each structural level and the main interactions between them. The microstructure is associated with the active clay minerals, while the macrostructure accounts for the larger-scale structure of the material. The model has been formulated considering concepts of classical and generalized plasticity theories. The generalized stress–strain rate equations are derived within a framework of multidissipative materials, which provides a consistent and formal approach when there are several sources of energy dissipation. The model is formulated in the space of stresses, suction and temperature; and has been implemented in a finite element code. The approach has been applied to explaining and reproducing the behaviour of expansive soils in a variety of problems for which experimental data are available. Three application cases are presented in this paper. Of particular interest is the modelling of an accidental overheating, that took place in a large-scale heating test. This test allows the capabilities of the model to be checked when a complex thermo-hydro-mechanical (THM) path is followed.
Abstract
The constitutive model presented in this work is built on a conceptual approach for unsaturated expansive soils in which the fundamental characteristic is the explicit consideration [...]
- 2
- read
A constitutive model for unsaturated soils: thermomechanical and computational aspects
D. Sheng, S. Sloan, A. Gens

Computational Mechanics (2004). Vol. 33 (6), pp. 453-465

Abstract
This paper first presents a complete formulation of a constitutive model that deals with the irreversible behaviour of unsaturated soils under various loading and drying/wetting conditions. A standard form of incremental stress-strain relations is derived. The constitutive model is then cast into the thermodynamical theories and verified using the thermomechanical principles. It is shown that hydraulic hysteresis does not contribute to the plastic dissipation, though it contributes to the plastic work. All plastic work associated with a plastic increment of the degree of saturation is stored and can be recovered in a reversed plastic increment of saturation. The incremental constitutive equations are also reformulated for implementation in finite element codes where displacements and pore pressures are primary unknowns. Qualitative predictions of the constitutive model show that incorporating two suction related yield surfaces and non-associated flow rules into the Barcelona Basic Model opens a full range of possibilities in modelling unsaturated soil behaviour
Abstract
This paper first presents a complete formulation of a constitutive model that deals with the irreversible behaviour of unsaturated soils under various loading and drying/wetting [...]
- 2
- read
The role of structure in the chemically induced deformations of FEBEX bentonite
G. Musso, E. Morales, A. Gens, E. Castellanos

Applied Clay Science (2003). Vol. 23 (1-4), pp. 229-237

Abstract
The paper presents the experimental results of an investigation aimed at understanding the role played by the soil structure in the evolution of chemo-mechanical-coupled processes in bentonite. The objective was pursued by subjecting samples with different structures to similar salinisation–desalinisation cycles. Samples were prepared at approximately the same void ratio by means of either static compaction at hygroscopic humidity or starting from slurries consolidated under mechanical loads. The investigation was carried out both from a macroscopic point of view (measuring the induced deformations) and from a microscopic point of view (ESEM analysis, mercury intrusion porosimetry). It is evidenced how the behaviour of the compacted samples differs from the one in the consolidated samples, especially as far as the evolution in time of the deformations is considered. An attempt to explain the differences by means of structural considerations is then provided.
Abstract
The paper presents the experimental results of an investigation aimed at understanding the role played by the soil structure in the evolution of chemo-mechanical-coupled processes [...]
- 2
- read
Tunnelling and swelling in triassic sulphate-bearing rocks: part II: case studies from Jura Mountains
I. Berdugo, E. Alonso, E. Romero, A. Gens

Epsilon (2009). Vol. 12, pp. 39-53

Abstract
Part II of this series of paper deals with the phenomenology of swelling in tunnels from Jura Mountains (Switzerland) excavated through the Gipskeuper and the Anhydritgruppe. The main features of expansions observed in the presented case studies are summarized and the performance of resisting and yielding support systems is compared. Evidences presented in this series of papers indicate that the transformation of anhydrite into gypsum is not a reasonable explanation for long-term expansive phenomena occurring in sulphate-bearing rocks. It is suggested that these phenomena are strongly related to rock degradation due to both tunneling induced drainage towards the bottom of excavations and tunneling induced ventilation.
Abstract
Part II of this series of paper deals with the phenomenology of swelling in tunnels from Jura Mountains (Switzerland) excavated through the Gipskeuper and the Anhydritgruppe. [...]
- 2
- read
Tunnelling and geotechnics: new horizons. Vote of thanks
R. Mair, A. Gens

Géotechnique (2008). Vol. 58 (9), pp. 736-736

Abstract
New developments in both the theory and the practice of tunnelling are covered in the lecture. The important relationship between tunnelling and geotechnics is highlighted, and recent advances in research and practice are described, drawing on model studies, theoretical developments and field measurements from case histories from around the world. Simplified plasticity models are presented that can be used by designers to assess ground movements and tunnel lining loads in complex ground conditions. The important role of pilot tunnels and in situ measurements to validate such models, drawing on a case history from Bolu, Turkey, and on other tunnelling projects, is described. Recent technical advances in earth pressure balance tunnelling are considered, illustrated by measurements from the Channel Tunnel Rail Link project, with emphasis on key factors influencing volume loss, such as face pressure, soil conditioning and effective screw conveyor operation. A recent case history in Bologna is described, in which the innovative use of directional drilling to install curved grout tubes was employed for a compensation grouting project in granular soils. Time-dependent ground movements and tunnel lining distortions occurring after tunnelling are discussed, their magnitude depending on the relative permeability of the tunnel lining and soil, the degree of anisotropy of the soil permeability, and the initial pore pressure prior to tunnelling. The effects of tunnelling-induced settlements on pipelines are considered, drawing on centrifuge tests and analytical solutions, and a new design approach is presented, taking into account the reduction of soil stiffness with increasing shear strain as a result of tunnel volume loss. The lecture concludes with a description of a distributed strain sensing technique using fibre optic technology, based on Brillouin optical time domain reflectometry (BOTDR), and its innovative application to field monitoring of a masonry tunnel subjected to new tunnel construction beneath it.
Abstract
New developments in both the theory and the practice of tunnelling are covered in the lecture. The important relationship between tunnelling and geotechnics is highlighted, [...]
- 2
- read
Efficiency of a borehole seal by means of pre-compacted bentonite blocks
M. Geet, G. Volckaert, W. Bastiaens, N. Maes, E. Weetjens, X. Sillen, B. Vallejan, A. Gens

Physics and Chemistry of the Earth (2007). Vol. 32 (1-7), pp. 123-134

Abstract
The backfilling and sealing of shafts and galleries is an essential part of the design of underground repositories for high-level radioactive waste. Part of the EC funded project RESEAL studied the feasibility of sealing off a borehole in plastic Boom Clay by means of pre-compacted bentonite blocks. Two bentonites, namely the FoCa and Serrata clay, have been used. Based on laboratory tests, the bentonite blocks had an initial dry density of about 1.8 g/cm3 to obtain a swelling pressure of about 4.4 MPa, corresponding to the in situ lithostatic stress, at full saturation. The set-up was equipped with several sensors to follow-up the behaviour of the seal and the surrounding host rock during hydration. Full saturation was reached after five months and was mainly reached by natural hydration. Swelling pressure was lower than originally foreseen due to the slow reconsolidation of the host rock. Later on, the efficiency of the seal with respect to water, gas and radionuclide migration was tested. The in situ measured permeability of the seals was about 5 × 10-13 m/s. A gas breakthrough experiment did not show any preferential gas migration through the seal. No evidences of a preferential pathway could be detected from 125I tracer test results
Abstract
The backfilling and sealing of shafts and galleries is an essential part of the design of underground repositories for high-level radioactive waste. Part of the EC funded [...]
- 2
- read
The soilmodels.info project
G. Gudehus, A. Amorosi, A. Gens, I. Herle, D. Kolymbas, D. Masin, D. Miui-Wood

International Journal for Numerical and Analytical Methods in Geomechanics (2008). Vol. 32 (12), pp. 1571-1572
- 2
- read
Implementation algorithm of a generalised plasticity model for swelling clays
M. Sanchez, A. Gens, L. Guimarães, S. Olivella

Computers and Geotechnics (2008). Vol. 35 (6), pp. 860-871

Abstract
A multi-mechanism generalisation of Sloan’s integration scheme for elasto-plastic laws has been developed in order to implement a double structure model for expansive clays into a FE code. The constitutive model is built on a conceptual approach for unsaturated expansive soils in which the fundamental characteristic is the explicit consideration of the two pore levels often present in expansive clays. The distinction between macro and microstructure provides the opportunity to take into account the dominant phenomena that affect the behaviour of each structural level and the main interactions between them. The model is formulated using concepts of classical and generalised plasticity theories. The integration scheme proposed can deal with the two plastic mechanisms defined in the model and can incorporate the effects of strains, suction and temperature in the stress integration process. A large scale heating test is analysed to check the capabilities of the implemented model to simulate an actual problem involving complex thermo-hydro-mechanical stress paths. The performance of the model has been very satisfactory and the proposed integration scheme has proved to be robust and efficient in solving a highly non-linear coupled problem.
Abstract
A multi-mechanism generalisation of Sloan’s integration scheme for elasto-plastic laws has been developed in order to implement a double structure model for expansive [...]
- 2
- read
THM and reactive transport analysis of expansive clay barrier in radioactive waste isolation
L. Guimarães, A. Gens, M. Sanchez, S. Olivella

Communications in numerical methods in engineering (2006). Vol. 22 (8), pp. 849-859

Abstract
A fully coupled formulation combining reactive transport and an existing thermo‐hydro‐mechanical (THM) code is briefly described. Special attention has been given to phenomena likely to be encountered in clay barriers used as part of containment systems of nuclear waste. The types of processes considered in the chemical formulation include hydrolysis, complex formation, oxidation/reduction reactions, acid/base reactions, precipitation/dissolution of minerals and cation exchange. Both kinetically controlled and equilibrium‐controlled reactions have been incorporated. The formulation has been implemented in the finite element code CODE_BRIGHT. An application is presented concerning the performance of a large scale in situ heating test simulating high‐level nuclear waste repository conditions.
Abstract
A fully coupled formulation combining reactive transport and an existing thermo‐hydro‐mechanical (THM) code is briefly described. Special attention has been given to phenomena [...]
- 2
- read
Aznalcóllar dam failure. Part 2: stability conditions and failure mechanisms
A. Gens, E. Alonso

Géotechniques (2006). Vol. 56 (3), pp. 185-201

Abstract
An analysis of the conditions that led to the failure of the Aznalcóllar dam is made in the paper. Pore water pressures prevailing in the foundation clay at the time of the failure have been established on the basis of piezometric observations made after the failure. A simplified consolidation analysis is first presented to interpret pore water pressure generation and dissipation and to evaluate the evolution of shear stresses along the potential failure plane. Both limit equilibrium and finite element analysis are used to back-analyse the failure and to derive representative strength parameters along the failure surface. Three-dimensional effects introduced by the layered nature of the foundation clay are then described. They provide an explanation for the location of the slide, which affected only the south-eastern portion of the embankment. The failure is examined in the final part of the paper from the perspective offered by the current knowledge of the strength behaviour of brittle clays. The significance of progressive failure is discussed, together with other factors that played a significant role in this case: the homogeneous nature and very low permeability of the foundation clay and the natural state of the clay, probably affected by some initial damage, which reduced the available strength along bedding planes.
Abstract
An analysis of the conditions that led to the failure of the Aznalcóllar dam is made in the paper. Pore water pressures prevailing in the foundation clay at the time [...]
- 2
- read
Analysis of the hydration of a bentonite seal in a deep radioactive waste repository
J. Vaunat, A. Gens

Engineering Geology (2005). Vol. 81 (3), pp. 317-328

Abstract
A deep geological repository for nuclear waste requires the backfilling and sealing of shafts and galleries to block any preferential path for radioactive contaminants. The paper presents the coupled hydromechanical analyses of an in situ test carried out in the HADES underground laboratory in Mol, Belgium. The test examines the effectiveness of an expansive clay seal in a horizontal borehole specifically drilled for this purpose. The analysis covers the phase of seal hydration up to saturation and subsequent pore pressure equilibration. Hydraulic and mechanical constitutive laws suited to expansive clay materials have been chosen for the analyses with all the parameters determined independently of the in situ test. A quite good agreement has been found between test observations and computed results suggesting that the numerical formulation employed is able to reproduce the main features of a real sealing system
Abstract
A deep geological repository for nuclear waste requires the backfilling and sealing of shafts and galleries to block any preferential path for radioactive contaminants. The [...]
- 2
- read
Reply to Comments on “Unsaturated soils: From constitutive modelling to numerical algorithms” by Daichao Sheng, Antonio Gens, Delwyn G. Fredlund and Scott W. Sloan
D. Sheng, A. Gens, D. Fredlund, S. Sloan

Computers and Geotechnics (2009). Vol. 36 (6), pp. 1100
- 2
- read
On constitutive modelling of unsaturated soils
A. Gens, M. Sánchez, D. Sloan

Acta Geotechnica (2006). Vol. 1 (3), pp. 137-147

Abstract
The paper presents a review of constitutive modelling of unsaturated soils. After a brief historical perspective, a number of existing constitutive models are classified and discussed according to the type of stress variables adopted in their formulation. Afterwards, attention is given to recent developments in the proposal of coupled hydraulic-mechanical models and the possibility of casting them in a sound thermodynamical framework. Finally, a double structure model for expansive soils is described. The incorporation of microstructural considerations and its use as a platform for incorporating the influence of new variables are highlighted.
Abstract
The paper presents a review of constitutive modelling of unsaturated soils. After a brief historical perspective, a number of existing constitutive models are classified and [...]
- 2
- read
Applications of multiphysical geomechanics in underground nuclear waste storage
A. Gens, B. Garitte, S. Olivella, J. Vaunat

European Journal of Environmental and Civil Engineering (2009). Vol. 13 (7-8), pp. 937-962

Abstract
Deep geological disposal in suitable host rocks is the favoured strategy for the storage and disposal of heat-emitting high level nuclear waste. A rational design of repositories requires a good understanding of the interacting thermo-hydro-mechanical phenomena that occur in the engineered barrier and adjacent rock. To this end, a multiphysical formulation is described that allows the performance of coupled THM analyses capable of reproducing observed phenomena. The formulation and computer code is applied to the simulation of two large scale tests: a mine-by test involving the excavation of a shaft in an argillaceous rock and a large-scale high- temperature heating test in fractured rock.
Abstract
Deep geological disposal in suitable host rocks is the favoured strategy for the storage and disposal of heat-emitting high level nuclear waste. A rational design of repositories [...]
- 2
- read
Relative performance of two unsaturated soil models using different constitutive variables
S. Wheeler, J. Pineda, D. Sheng, A. Gens

Canadian Geotechnical Journal (2014). Vol. 51 (12), pp. 1423-1437

Abstract
Mechanical and water retention behaviour of unsaturated soils is investigated in the context of two well established coupled constitutive models, each of which is formulated in terms of a different set of stress state variables or constitutive variables. Incremental relationships describing the volume change and variation of the degree of saturation are derived for each model. These incremental relationships are used to simulate a set of experimental tests on compacted Speswhite kaolin previously reported in the literature. Six individual tests, involving isotropic compression and various forms of shearing, are analyzed in the context of the incremental forms developed, and the model predictions are then compared against experimental results. The results show that, although each constitutive model uses a different set of constitutive variables and a different scheme for coupling mechanical and water retention behaviour, the two sets of model predictions are similar and both sets provide a reasonable match to the experimental results, suggesting that both models are able to capture the relevant features of unsaturated soil behaviour, despite expressing the constitutive laws in different ways.
Abstract
Mechanical and water retention behaviour of unsaturated soils is investigated in the context of two well established coupled constitutive models, each of which is formulated [...]
- 2
- read
Multi-scale analysis of cone penetration test (CPT) in a virtual calibration chamber
J. Butlanska, M. Arroyo, A. Gens, C. O'Sullivan

Canadian Geotechnical Journal (2014). Vol. 51 (1), pp. 51-66

Abstract
A virtual calibration chamber was developed using a three-dimensional (3D) discrete element method (DEM) to perform cone penetration tests (CPTs) on a discrete analogue of Ticino sand. The macroscale response of the DEM model was previously shown to be in good quantitative agreement with that of analogous physical models. In the current study the performance of the model at meso and microscale levels of resolution is examined. The microscale response is examined using particle displacements and contact force distributions. The mesoscale behaviour is examined using stress and strain fields obtained through appropriate averaging and interpolating procedures. Four CPTs are examined at the steady-state penetration stage. The effects of radial boundary conditions, initial stress state, initial average density, and particle rotational inertia are examined. The ability of the micro and mesoscale data to identify and explain the relevant mechanisms underlying the significant differences in the macroscale response of the models is discussed. Comparisons with similar phenomena observed in physical tests are also highlighted.
Abstract
A virtual calibration chamber was developed using a three-dimensional (3D) discrete element method (DEM) to perform cone penetration tests (CPTs) on a discrete analogue of [...]
- 2
- read
Thermal-hydraulic-mechanical (THM) behaviour of a large-scale in situ heating experiment during cooling and dismantling
M. Castilla, A. Gens, L. Guimarães

Canadian Geotechnical Journal (2012). Vol. 49 (10), pp. 1169-1195

Abstract
A geological disposal facility for high-level radioactive waste (HLW) encompasses both natural (host rock) and (generally clay-based) engineered barriers. Many processes can influence, either positively or negatively, the effectiveness of the safety functions of isolation and retardation. This paper focuses on the analysis of a large-scale heating test when subjected to cooling and subsequent partial dismantling. The experiment reproduces the conditions of an HLW repository at full scale under realistic conditions. Key thermal, hydraulic, and mechanical (THM) variables, such as temperature, relative humidity, stresses, and fluid pressures, were measured in the clay barrier and surrounding rock. The experimental observations recorded during the cooling down and clay barrier excavation are analyzed in light of a fully coupled THM finite element formulation. This analysis has provided the opportunity to explore the behaviour of the clay and natural barriers under conditions very relevant for the repository performance but not analyzed previously. Overall, the model predictions are quite satisfactory when compared against experimental observations. Furthermore, model predictions for a period of 20 years, including the transient phase induced by the partial dismantling, are also presented. This additional analysis has allowed a better understanding of the effect of thermal gradient on long-term clay hydration.
Abstract
A geological disposal facility for high-level radioactive waste (HLW) encompasses both natural (host rock) and (generally clay-based) engineered barriers. Many processes can [...]
- 2
- read
Steady state of solid-grain interfaces during simulated CPT
J. Butlanska, M. Arroyo, A. Gens

Studia Geotechnica et Mechanica (2013). Vol. XXXV (4), pp. 13-22

Abstract
It has recently been shown (Arroyo et al. [1]) that 3D DEM models are able to reproduce with reasonable accuracy the macroscopic response of CPT performed in calibration chambers filled with sand. However, the cost of each simulation is an important factor. Hence, to achieve manageable simulation times the discrete material representing the sand was scaled up to sizes that were more typical of gravel than sand. A side effect of the scaled-up discrete material size employed in the model was an increased fluctuation of the macro-response that can be filtered away to observe a macroscopic steady-state cone resistance. That observation is the starting point of this communication, where a series of simulations in which the size ratio between penetrometer and particles is varied are systematically analyzed. A micromechanical analysis of the penetrometer-particle interaction is performed. These curves reveal that a steady state is arrived also at the particle-cone contact level. The properties of this dynamic interface are independent of the initial density of the granular material.
Abstract
It has recently been shown (Arroyo et al. [1]) that 3D DEM models are able to reproduce with reasonable accuracy the macroscopic response of CPT performed in calibration chambers [...]
- 2
- read
Effect of thermo-coupled processes on the behaviour of a clay barrier submitted to heating and hydration
M. Castilla, A. Gens, S. Olivella

Anais da Academia Brasileira de Ciências (2010). Vol. 82 (1), pp. 153-168

Abstract
The storage of high level radioactive waste is still an unresolved problem of the nuclear industry, being geological disposal the most favoured option and, naturally, the one requiring the strongest geo-mechanical input. Most conceptual designs for the deep geological disposal of nuclear waste envisage placing the canisters containing the waste in horizontal drifts or vertical boreholes. The empty space surrounding the canisters is filled by an engineered barrier often made up of compacted swelling clay. In the barrier and the near field, significant thermo-hydro-mechanical (THM) phenomena take place that interact in a complex way. A good understanding of THM issues is, therefore, necessary to ensure a correct performance of engineered barriers and seals. The conditions of the bentonite in an engineered barrier for high-level radioactive waste disposal are being simulated in a mock-up heating test at almost scale, at the premises of CIEMAT in Madrid. The evolution of the main Thermo-Hydro-Mechanical (THM) variables of this test are analysed in this paper by using a fully coupled THM formulation and the corresponding finite element code. Special emphasis has been placed on the study of the effect of thermo-osmotic flow in the hydration of the clay barrier at an advanced staged of the experiment
Abstract
The storage of high level radioactive waste is still an unresolved problem of the nuclear industry, being geological disposal the most favoured option and, naturally, the [...]
- 2
- read
Modelling thermo-hydro-mechano-chemical interactions for nuclear waste disposal
A. Gens, L. Guimarães, S. Olivella, M. Sanchez

Journal of rock mechanics and geotechnical engineering (2010). Vol. 2 (2), pp. 97-102

Abstract
A fully coupled thermo-hydro-mechano-chemical (THMC) formulation is described in this paper. Special attention is paid to phenomena likely to be encountered in clay barriers used as engineered barriers in the disposal of nuclear radioactive waste. The types of processes considered in the chemical formulation include hydrolysis, complex formation, oxidation/reduction reactions, acid/base reactions, precipitation/dissolution of minerals and cation exchange. Both kinetics- and equilibrium-controlled reactions are incorporated. The formulation is implemented in a numerical code. An application is presented concerning the performance of a large-scale in-situ heating test simulating high-level radioactive waste repository conditions.
Abstract
A fully coupled thermo-hydro-mechano-chemical (THMC) formulation is described in this paper. Special attention is paid to phenomena likely to be encountered in clay barriers [...]
- 2
- read
Hydromechanical behaviour of a heterogeneous compacted soil: experimental observations and modelling
A. Gens, B. Vallejan, M. Castilla, C. Imbert, M. Villar, M. Geetl

Géotechnique (2011). Vol. 61 (5), pp. 367-386

Abstract
The paper describes a theoretical and experimental study of the coupled hydromechanical behaviour of a compacted mixture of bentonite powder and bentonite pellets intended as sealing material in underground repositories for nuclear waste. One of the main advantages of the use of powder/pellets mixtures is the reduction of the compaction effort required to achieve the value of average dry density necessary to attain the required swelling potential. However, the heterogeneous fabric of the material requires special approaches in order to describe adequately its behaviour during hydration. A double porosity formulation is presented to account for the presence of two distinct structural levels in the material. Hydraulic equilibrium between the two porosities is not assumed; instead a water exchange term between them is postulated. The formulation is applied to the modelling of a number of one-dimensional swelling pressure tests performed in the CEA (Commisariat à l'Énergie Atomique, France) and CIEMAT (Spain) laboratories. A very satisfactory quantitative description of the experimental observations is obtained that includes a number of complex behaviour features such as size effects and non-monotonic development of swelling pressures. Some microfabric observations using X-ray tomography and mercury intrusion porosimetry lend support to the conceptual approach adopted. The formulation is then applied to the analysis of a long-term large-scale sealing test performed at the Hades underground facility in Belgium, using the same set of hydraulic and mechanical parameters employed in the modelling of the laboratory tests. Although the field observations exhibit a much higher degree of scatter, the basic behaviour of the field sealing test is satisfactorily simulated. A formulation that incorporates basic features of the microfabric of the mixture is thus able to span successfully over a large range of space and time scales.
Abstract
The paper describes a theoretical and experimental study of the coupled hydromechanical behaviour of a compacted mixture of bentonite powder and bentonite pellets intended [...]
- 2
- read
Standard penetration testing in a virtual calibration chamber
N. Zhang, M. Arroyo, M. Ciantia, A. Gens, J. Butlanska

Computers and Geotechnics (2019). Vol. 111, pp. 277-289

Abstract
The virtual calibration chamber technique, based on the discrete element method, is here applied to study the standard penetration test (SPT). A macro-element approach is used to represent a rod driven with an impact like those applied to perform SPT. The rod is driven into a chamber filled with a scaled discrete analogue of a quartz sand. The contact properties of the discrete analogue are calibrated simulating two low-pressure triaxial tests. The rod is driven changing input energy and controlling initial density and confinement stress. Energy-based blowcount normalization is shown to be effective. Results obtained are in good quantitative agreement with well-accepted experimentally-based relations between blowcount, density and overburden. It is also shown that the tip resistance measured under impact dynamic penetration conditions is close to that under constant velocity conditions, hence supporting recent proposals to relate CPT and SPT results
Abstract
The virtual calibration chamber technique, based on the discrete element method, is here applied to study the standard penetration test (SPT). A macro-element approach is [...]
- 2
- read
Fully coupled thermo-hydro-mechanical double-porosity formulation for unsaturated soils
M. Castilla, A. Gens, M. Villar, S. Olivella

International journal of geomechanics (2016). Vol. 16 (6), pp. D4016015-1/D4016015-17 (Preprint)

Abstract
This work presents a fully coupled formulation developed to handle engineering problems in unsaturated (and saturated) soils that present two dominant void levels. The proposed framework assumes the presence of two porous media linked through a mass-transfer term between them. In its more general form, the proposed approach allows the consideration of nonisothermal multiphase flow coupled with the mechanical problem. The double-porosity formulation was implemented in a finite-element code and has been used to analyze a variety of engineering problems. The approach is especially suitable for cases in which the material exhibits a strong coupling between the mechanical and the hydraulic problems in both media, such as with swelling clays. For those types of problems, the proposed formulation is used in conjunction with the mechanical double-structure model already proposed by the authors. This paper presents the coupled formulation and the application of the proposed approach to problems involving expansive unsaturated clays. Very satisfactory results were obtained in these analyses
Abstract
This work presents a fully coupled formulation developed to handle engineering problems in unsaturated (and saturated) soils that present two dominant void levels. The proposed [...]
- 2
- read
Discussion on 'Effects of particle breakage and stress reversal on the behaviour of sand around displacement piles'
F. Altuhafi, R. Jardine, V. Georgiannou, W. Moinet, M. Ciantia, M. Arroyo, A. Gens

Géotechnique (2019). Vol. 69 (11), pp. 1029-1030
- 2
- read
Characterisation of the multi-scale fabric features of high plasticity clays
F. Cotecchia, S. Guglielmi, F. Cafaro, A. Gens

Géotechnique Letters (2019). Vol. 9 (4), pp. 361-368

Abstract
An investigation of the microstructural features of a high-plasticity clay, in both its natural conditions and reconstituted in the laboratory, is described. Scanning electron microscopy is used here to characterise the fabric at different magnifications, while image processing of the micrographs delivers a quantitative assessment of the fabric orientation. The results of energy-dispersive X-ray spectroscopy and swelling tests, as reported in a previous study by the authors, are used to characterise the bonding nature and strength, as well as mercury intrusion porosimetry to investigate clay porosimetry. Despite their identical composition, the natural and the reconstituted clay have experienced different deposition and loading history, generating different microstructural features that are shown to underlie their differences in state. For both clays, one-dimensional (1D) compression to medium–high pressures is seen to determine a well-oriented medium magnification fabric. However, larger-scale observations and the corresponding image processing results reveal non-uniform local fabric features, hence making fabric characterisation dependent on the scale of analysis and bringing about the issue of identifying the clay micro-scale representative element volume relating to the clay macro-behaviour. The micro-REV is identified for the clays under study and its connection with the macro-behaviour characterised. The microstructural evolution induced by 1D compression to very high pressures is shown to concern mainly the clay porosity and porosimetry, the fabric orientation being steady, thus explaining the isotropic hardening observed in laboratory tests.
Abstract
An investigation of the microstructural features of a high-plasticity clay, in both its natural conditions and reconstituted in the laboratory, is described. Scanning [...]
- 2
- read
Micromechanical inspection of incremental behaviour of crushable soils
M. Ciantia, M. Arroyo, C. O'Sullivan, A. Gens

Acta Geotechnica (2019). Vol. 14 (5), pp. 1337-1356

Abstract
In granular soils grain crushing reduces dilatancy and stress obliquity enhances crushability. These are well-supported specimen-scale experimental observations. In principle, those observations should reflect some peculiar micromechanism associated with crushing, but which is it? To answer that question the nature of crushing-induced particle-scale interactions is here investigated using an efficient DEM model of crushable soil. Microstructural measures such as the mechanical coordination number and fabric are examined while performing systematic stress probing on the triaxial plane. Numerical techniques such as parallel and the newly introduced sequential probing enable clear separation of the micromechanical mechanisms associated with crushing. Particle crushing is shown to reduce fabric anisotropy during incremental loading and to slow fabric change during continuous shearing. On the other hand, increased fabric anisotropy does take more particles closer to breakage. Shear-enhanced breakage appears then to be a natural consequence of shear-enhanced fabric anisotropy. The particle crushing model employed here makes crushing dependent only on particle and contact properties, without any pre-established influence of particle connectivity. That influence does not emerge, and it is shown how particle connectivity, per se, is not a good indicator of crushing likelihood
Abstract
In granular soils grain crushing reduces dilatancy and stress obliquity enhances crushability. These are well-supported specimen-scale experimental observations. In principle, [...]
- 2
- read
Presa de Caruachi. Estudio del comportmiento hidráulico de las compuertas de los conductos de desvío
M. Sánchez-Juny, D. Niñerola, J. Pomares, E. Egusquiza, J. Dolz, F. Quintero, F. Abadía

Revista de Obras Públicas (2002). N. 3423, pp. 12-26

Abstract
Se presenta el estudio desarrollado en el Laboratorio de Modelos Reducidos del Dpto. de Ing. Hidráulica, Marítima y Ambiental de la UPC, para el análisis del comportamiento hidráulico de las compuertas a utilizar en la operación de cierre de la presa de Caruachi en el río Caroní (Venezuela). Se han analizado la capacidad de desagüe, la aireación de los conductos de desvío, las presiones en los mismos durante la operación, así como las vibraciones y fuerza vertical descendente (down-pull) sobre las compuertas. The present article describes the study carried out at the Reduced Model Laboratory (Hydraulic, Maritime and Environmental Engineering Department, UPC) into the hydraulic behaviour of the gates employed in the closing operation of the Caruachi dam on the River Caroní (Venezuela). An analysis is made of the discharge and aeration capacity of the diversión conduits, the operation pressures in the same and the vibration and down-pull on the gates.
Abstract
Se presenta el estudio desarrollado en el Laboratorio de Modelos Reducidos del Dpto. de Ing. Hidráulica, Marítima y Ambiental de la UPC, para el análisis [...]
- 2
- read
Preserving steady-state in one-dimensional finite-volume computations of river flow
E. Bladé, M. Gómez, M. Sánchez-Juny, J. Dolz

Journal of Hydrology Engineering (2008). Vol. 134 (9), pp. 1343-1347

Abstract
When using finite-volume methods and the conservative form of the Saint Venant equations in one-dimensional flow computations, it is important to establish the correct balance between the discretized flux vector and the geometric source terms. Over the last few years various improvements to numerical schemes have been presented to achieve this correct balance, focusing on the capability to simulate water at rest on irregular geometries (C-property). In this paper it is shown that common schemes can lead to energy-violating solutions in the case of steady flow. We present developments based on the Roe TVD finite-volume scheme for one-dimensional Saint Venant equations, which results in a method that not only satisfies the C-property, but also preserves the correct steady flow when stationary boundary conditions are used. We also present a totally irregular channel test case for the verification of the method.
Abstract
When using finite-volume methods and the conservative form of the Saint Venant equations in one-dimensional flow computations, it is important to establish the correct balance [...]
- 2
- read
Interplay of packing and flip-flop in local bilayer deformation. How phosphatidylglycerol could rescue mitochondrial function in a cardiolipin-deficient yeast mutant
N. Khalifat, M. Rahimi, A. Bitbol, M. Seigneuret, J. Fournier, N. Puff, M. Arroyo, M. Angelova

Biophysical journal (2014). Vol. 107 (4), pp. 879-890 (preprint)

Abstract
In a previous work, we have shown that a spatially localized transmembrane pH gradient, produced by acid micro-injection near the external side of cardiolipin-containing giant unilamellar vesicles, leads to the formation of tubules that retract after the dissipation of this gradient. These tubules have morphologies similar to mitochondrial cristae. The tubulation effect is attributable to direct phospholipid packing modification in the outer leaflet, that is promoted by protonation of cardiolipin head-groups. In this study, we compare the case of cardiolipin-containing giant unilamellar vesicles with that of giant unilamellar vesicles that contain phosphatidylglycerol (PG). Local acidification also promotes formation of tubules in the latter. However, compared with cardiolipin-containing giant unilamellar vesicles the tubules are longer, exhibit a visible pearling, and have a much longer lifetime after acid micro-injection is stopped. We attribute these differences to an additional mechanism that increases monolayer surface imbalance, namely inward PG flip-flop promoted by the local transmembrane pH gradient. Simulations using a fully nonlinear membrane model as well as geometrical calculations are in agreement with this hypothesis. Interestingly, among yeast mutants deficient in cardiolipin biosynthesis, only the crd1-null mutant, which accumulates phosphatidylglycerol, displays significant mitochondria! activity. Our work provides a possible explanation of such a property and further emphasizes the salient role of specific lipids in mitochondria! function. n a previous work, we have shown that a spatially localized transmembrane pH gradient, produced by acid micro-injection near the external side of cardiolipin-containing giant unilamellar vesicles, leads to the formation of tubules that retract after the dissipation of this gradient. These tubules have morphologies similar to mitochondrial cristae. The tubulation effect is attributable to direct phospholipid packing modification in the outer leaflet, that is promoted by protonation of cardiolipin headgroups. In this study, we compare the case of cardiolipin-containing giant unilamellar vesicles with that of giant unilamellar vesicles that contain phosphatidylglycerol (PG). Local acidification also promotes formation of tubules in the latter. However, compared with cardiolipin-containing giant unilamellar vesicles the tubules are longer, exhibit a visible pearling, and have a much longer lifetime after acid micro-injection is stopped. We attribute these differences to an additional mechanism that increases monolayer surface imbalance, namely inward PG flip-flop promoted by the local transmembrane pH gradient. Simulations using a fully nonlinear membrane model as well as geometrical calculations are in agreement with this hypothesis. Interestingly, among yeast mutants deficient in cardiolipin biosynthesis, only the crd1-null mutant, which accumulates phosphatidylglycerol, displays significant mitochondrial activity. Our work provides a possible explanation of such a property and further emphasizes the salient role of specific lipids in mitochondrial function.
Abstract
In a previous work, we have shown that a spatially localized transmembrane pH gradient, produced by acid micro-injection near the external side of cardiolipin-containing giant [...]
- 1
- read
The landslide of Cortes de Pallas, Spain
E. Alonso, A. Gens, A. Lloret

Géotechnique (1993). Vol. 43 (4), pp. 507-521

Abstract
A large landslide in Cretaceous limestone and marl formations, reactivated by quarry excavations, has been stabilized by weight-transfer procedures designed by using a conventional limit-equilibrium analysis. The analysis was based on strength parameters derived from a back-analysis of the conditions leading to instability. Slide reactivation, excavation and Ailing have also been modelled by a finite element analysis in which the sliding surface has been represented by elastoplastic joint elements. This has provided important information regarding the sliding mechanisms and the effects of the remedial measures. Shear strength parameters determined in the laboratory are compared with those obtained from back-analysis. A significant discrepancy was reconciled when it was found that the sliding surface was located in a very thin and continuous clay layer of uncertain origin; possible mechanisms explaining the presence of the clay layer are suggested. The case demonstrated the importance of knowing in detail the geometry of the sliding surface, proves the value of field instrumentation and shows the fundamental role that geological details play in landslide problems.
Abstract
A large landslide in Cretaceous limestone and marl formations, reactivated by quarry excavations, has been stabilized by weight-transfer procedures designed by using a conventional [...]
- 1
- read
Coupled analysis of a backfill hydration test
E. Alonso, A. Lloret, C. Delahaye, A. Gens, G. Volckaert

International Journal for Numerical and Analytical Methods in Geomechanics (1998). Vol. 1 (1), pp. 10-25

Abstract
BACCHUS2 in situ isothermal wetting experiment has been analysed by means of a coupled flow-deformation approach. Backfill material, a mixture of Boom clay powder and high density pellets, has been extensively tested in the laboratory in order to determine its hydraulic and mechanical properties. Parameters of constitutive equations were derived from this experimental data base. Two mechanical constitutive models have been used in the simulation of the 'in situ' experiment: a state surface approach and an elastoplastic model. Calculations have shown several features of the hydration process which help to understand the behaviour of expansive clay barriers. Predictions using both models have been compared with each other and with actual measurement records. This has allowed a discussion of the comparative mertis of both approaches and the identiÞcation of some critical parameters of backfill behaviour. Overall agreement between calculations and field measurements is encouraging and shows the potential of the methods developed to model the behaviour of engineered clay barriers in the context of nuclear waste disposal.
Abstract
BACCHUS2 in situ isothermal wetting experiment has been analysed by means of a coupled flow-deformation approach. Backfill material, a mixture of Boom clay powder and high [...]
- 1
- read
A constitutive model for rock joints formulation and numerical implementation
A. Gens, I. Carol, E. Alonso

Computers and Geotechnics (1990). Vol. 9 (1-2), pp. 3-20

Abstract
An elastoplastic constitutive law for describing the three-dimensional mechanical behaviour of rock joints is presented. The model is intended for use in numerical analysis and is formulated with sufficient flexibility so that it can reproduce a wide range of observed joint stress-strain behaviour. An hyperbolic failure criterion is shown to fit well reported joint strength data and the same type of function is adopted to define the family of yield surfaces. The evolution of hardening/softening is controlled by the total length of the plastic tangential strain path. Locking behaviour under normal loading and dilatancy varying with stress and strain level are also accounted for. Examples of application of the model to the reproduction of test results are presented. The model can be generalized to include anisotropy effects. Finally, some aspects of the procedures used in the numerical implementation of the constituive law are described.
Abstract
An elastoplastic constitutive law for describing the three-dimensional mechanical behaviour of rock joints is presented. The model is intended for use in numerical analysis [...]
- 1
- read
Double structure THM analysis of a heating test in a fractured tuff incorporating intrinsic permeability variations
S. Olivella, A. Gens

International Journal of Rock Mechanics and Mining Sciences (2005). Vol. 42 (5-6), pp. 667-679

Abstract
This paper presents thermo-hydro-mechanical (THM) analyses simulating the Drift Scale Test (DST) performed at Yucca Mountain. A double structure approach based on two superimposed domains is adopted. Intrinsic permeability changes with deformations imply full THM coupling. Temperatures and gas permeabilities were measured during 4 years and are used to validate the model. Measured gas permeability variations show patterns that are successfully explained by the model calculations. These gas permeability variations may be attributed to thermo-hydraulic effects, and also to mechanical effects. Different cases of intrinsic permeability variations have been considered in the model and their influence on the calculated temperatures, degree of saturations and gas permeabilities are presented. Volumetric deformation, in contraction or dilatancy, implies changes in the aperture of rock fractures that in turn lead to changes in intrinsic permeability. Dilatancy, caused by shear stresses, increases intrinsic permeability. Consideration of this factor contributes significantly to improve the agreement of calculated gas permeability with the measured values obtained during the DST experiment.
Abstract
This paper presents thermo-hydro-mechanical (THM) analyses simulating the Drift Scale Test (DST) performed at Yucca Mountain. A double structure approach based on two [...]
- 1
- read
Mechanical behaviour of heavily compacted bentonite under high suction changes
A. Lloret, M. Villar, M. Sanchez, A. Gens, X. Pintado, E. Alonso

Géotechniques (2003). Vol. 53 (1), pp. 27-40

Abstract
The paper reports the results of an experimental study carried out on a bentonite compacted to a dry density of up to 1·7 Mg=m3, a high value for this type of soil. The soil fabric has been studied using a variety of techniques, revealing a clear bimodal pore distribution that corresponds to two distinct structural levels: a microstructural one and a macrostructural one. The main testing programme has been performed using oedometers especially designed to apply a very large range of suctions. By applying the axis-translation technique (using nitrogen as the gas fluid), it has been possible to reach suctions up to 15 MPa. The higher suction range has been achieved by applying a controlled atmosphere where the relative humidity has been fixed by a solution of sulphuric acid or salts. In this way suctions up to 550 MPa could be reached. The maximum vertical stress that could be applied in the apparatus was 10 MPa. Two types of test have been carried out: (a) tests in which a combination of loading paths at constant suction and drying/wetting paths at constant load were applied; (b) swelling tests under constant-volume conditions in order to determine the swelling pressure and the stress path followed during wetting. The results of the experimental programme are examined, taking into account the role of the soil fabric in controlling observed mechanical behaviour. In addition, the results of the laboratory tests are reproduced and interpreted using a generalised plasticity model that considers explicitly the interaction between macrostructure and microstructure. In this way, it is possible to achieve a more complete understanding of the mechanisms that underlie observed behaviour, and in particular the interplay between the two structural levels
Abstract
The paper reports the results of an experimental study carried out on a bentonite compacted to a dry density of up to 1·7 Mg=m3, a high value for this type of soil. [...]
- 1
- read
Analysis of tunnel excavation in London Clay incorporating soil structure
N. González, M. Rouainia, M. Arroyo, A. Gens

Géotechnique (2012). Vol. 62 (12), pp. 1095-1109

Abstract
Recent studies on London Clay have identified a number of different units in the geological profile, and have highlighted the role of soil structure in mechanical behaviour. In fact, structure is the dominant factor determining the differences in the mechanical response of different units. In the paper, numerical analyses simulating the undrained excavation of a tunnel in St James's Park are presented. London Clay behaviour is characterised by a kinematic-hardening structured soil model incorporating structure and stiffness degradation. The parameters and initial conditions are based on a careful calibration that takes into account the presence of different units within the London Clay formation and the different degrees of soil structure. The analyses performed result in a very satisfactory reproduction of the magnitude and patterns of short-term surface and subsurface displacements, as well as pore pressures. The paper concludes with a discussion of the results in the context of other analyses performed previously, and puts forward some considerations concerning design issues.
Abstract
Recent studies on London Clay have identified a number of different units in the geological profile, and have highlighted the role of soil structure in mechanical behaviour. [...]
- 1
- read
Thermal conductivity of argillaceous rocks: determination methodology using in situ heating tests
B. Garitte, A. Gens, J. Vaunat, G. Armand

Rock Mechanics and Rock Engineering (2012). Vol. 47, pp. 111-129

Abstract
This study focuses on the characterisation of thermal conductivity for three potential host rocks for radioactive waste disposal. First, the heat conduction process is reviewed on the basis of an analytical solution and key aspects related to anisotropic conduction are discussed. Then the existing information on the three rocks is summarised and a broad uncertainty range of thermal conductivity is estimated based on the mineralogical composition. Procedures to backanalyse the thermal conductivity on the basis of in situ heating tests are assessed and a methodology is put forward. Finally, this methodology is used to estimate the impact of experimental uncertainties and applied to the four in situ heating tests. In the three potential host rocks, a clear influence of the bedding planes was identified and anisotropic heat conduction was shown to be necessary to interpret the observed temperature field. Experimental uncertainties were also shown to induce a larger uncertainty on the anisotropy ratio than on the equivalent thermal conductivity defined as the geometric mean of the thermal conductivity in the three principal directions.
Abstract
This study focuses on the characterisation of thermal conductivity for three potential host rocks for radioactive waste disposal. First, the heat conduction process is reviewed [...]
- 1
- read
Simulation of cement-improved clay structures with a bonded elasto-plastic model: A practical approach
M. Arroyo, M. Ciantia, R. Castellanza, A. Gens, R. Nova

Computers and Geotechnics (2012). Vol. 45, pp. 140-150

Abstract
Engineering practice has usually dealt with the treated soil bodies using simplistic constitutive models (e.g. elastic perfectly-plastic Mohr–Coulomb). In this paper, a more refined bonded elasto-plastic model is here applied, with emphasis on the ease of calibration. Empirical studies have identified the ratio of cement content to the cured mixture void ratio as a controlling variable for mechanical response. This observation is elaborated upon to show that measuring porosity and unconfined compressive strength is enough to initialize the state variables of a bonded elasto-plastic model. Data from cement-improved Bangkok clay is employed to illustrate and validate the calibration procedure proposed. The structure-scale consequences of the constitutive model choice for the soil–cement are explored through the parametric analysis of an idealized excavation problem. A treated soil–cement slab is characterized by increasing cement contents in the clay–cement mixture. Two sets of parametric analysis are run characterizing the clay–cement either with a linear elastic-perfectly plastic model or with the bonded elasto-plastic model. The same values of unconfined compressions strength (UCS) are specified for the two models to make comparisons meaningful. Results from both series of analysis are compared highlighting the differences in predicted behaviour of the retaining wall and the excavation stability.
Abstract
Engineering practice has usually dealt with the treated soil bodies using simplistic constitutive models (e.g. elastic perfectly-plastic Mohr–Coulomb). In this [...]
- 1
- read
THM analysis of a large-scale heating test incorporating material fabric changes
M. Castilla, A. Gens, S. Olivella

International Journal of Numerical and Analytical Methods in Geomechanics (2012). Vol. 36 (4), pp. 391-421

Abstract
Engineered barriers are basic elements in the design of repositories for the isolation of high‐level radioactive waste. This paper presents the thermo‐hydro‐mechanical (THM) analysis of a clay barrier subjected to heating and hydration. The study focuses on an ongoing large‐scale heating test, at almost full scale, which is being carried out at the CIEMAT laboratory under well‐controlled boundary conditions. The test is intensely instrumented and it has provided the opportunity to study in detail the evolution of the main THM variables over a long period of time. Comprehensive laboratory tests carried out in the context of the FEBEX and NF‐PRO projects have allowed the identification of the model parameters to describe the THM behaviour of the compacted expansive clay. A conventional THM approach that assumes the swelling clay as a single porosity medium has been initially adopted to analyse the evolution of the test. The model was able to predict correctly the global THM behaviour of the clay barrier in the short term (i.e. for times shorter than three years), but some model limitations were detected concerning the prediction of the long‐term hydration rate. An additional analysis of the test has been carried out using a double structure model to describe the actual behaviour of expansive clays. The double structure model explicitly considers the two dominant pore levels that actually exist in the FEBEX bentonite and it is able to account for the evolution of the material fabric. The simulation of the experiment using this enhanced model provides a more satisfactory reproduction of the long‐term experimental results. It also contributes to a better understanding of the observed test behaviour and it provides a physically based explanation for the very slow hydration of the barrier.
Abstract
Engineered barriers are basic elements in the design of repositories for the isolation of high‐level radioactive waste. This paper presents the thermo‐hydro‐mechanical [...]
- 1
- read
Interpretation of unsaturated soil behaviour in the stress. Saturation space, I: volume change and water retention behaviour
N. Zhou, D. Sheng, S. Scott, A. Gens

Computers and Geotechnics (2012). Vol. 43, pp. 178-187

Abstract
Unsaturated soil behaviour, such as volume change, shear strength and yield stress, is usually interpreted and modelled in terms of stress and suction. This approach is consistent with laboratory tests where suction is a controllable variable. However, it also suffers some limitations. This paper (Parts I and II) presents an alternative approach for interpreting unsaturated soil behaviour, which is built in the space of stress versus degree of saturation. In Part I, a new volume change equation is proposed in terms of stress and degree of saturation, to give a better explanation to the non-linear change of soil compressibility under constant suctions. The soil compression index is assumed to be a function of the effective degree of saturation and is interpolated from the known compressibility at the fully saturated state and that at a dry state. An alternative approach to simulate hydraulic hysteresis and hydro-mechanical interaction is then introduced, which enables the calculation of the effective degree of saturation under complex stress and suction paths. The proposed volume change equation and the approach to describe saturation variation, which are two fundamental aspects to establish constitutive laws for unsaturated soils, are validated against a variety of experimental data in literature.
Abstract
Unsaturated soil behaviour, such as volume change, shear strength and yield stress, is usually interpreted and modelled in terms of stress and suction. This approach [...]
- 1
- read
Heating pulse tests under constant volumen on natural Boom clay.
A. Lima, E. Romero, A. Gens, J. Muñoz, X. Li

Journal of rock mechanics and geotechnical engineering (2010). Vol. 2 (2), pp. 124-128

Abstract
Boom clay formation is a potential natural host rock for geological disposal of high-level nuclear waste in Belgium. Heating pulse tests with controlled power supply (maximum temperature was limited to 85°C) and controlled hydraulic boundary conditions were performed under nearly constant volume conditions to study the impact of thermal loading on the clay formation. Selected test results of intact borehole samples retrieved in horizontal direction are presented and discussed. The study focuses on the time evolution of temperature and pore water pressure changes along heating and cooling paths, i.e. pore pressure build-up during quasi-undrained heating and later dissipation at constant temperature.
Abstract
Boom clay formation is a potential natural host rock for geological disposal of high-level nuclear waste in Belgium. Heating pulse tests with controlled power supply (maximum [...]
- 1
- read
Unsaturated soils: models algorithm and applications
A. Gens, D. Sloan

Computers and Geotechnics (2008). Vol. 35 (6), pp. 809
- 1
- read
A mechanism contributing to subsidence above gas reservoirs
A. Menin, V. Salomoni, R. Santagiuliana, L. Simoni, A. Gens, B. Schrefler

International Journal for Computational Methods in Engineering Science and Mechanics (2008). Vol. 9 (5), pp. 270-287

Abstract
This paper aims to demonstrate that capillary effects and structural collapse can not be ruled out as significant factors in the development of subsidence occurring above gas fields. These phenomena provide sound explanations for continuing surface settlements when reservoir pore pressures stabilize and for additional settlements occurring even after the end of gas production. Conventional subsidence models fail to simulate this settlement behavior. Capillary effects also explain the lower rock compressibilities observed in gas-bearing strata as compared to the values obtained in the laboratory from fully saturated samples. Taking into account these aspects, the observed subsidence above a reservoir in the North Adriatic basin, Italy, is studied in detail.
Abstract
This paper aims to demonstrate that capillary effects and structural collapse can not be ruled out as significant factors in the development of subsidence occurring above [...]
- 1
- read
Modelling unsaturated soil behaviour during normal consolidation and at critical state
D. Gallipoli, A. Gens, G. Chen, F. D'Onza

Computers and Geotechnics (2008). Vol. 35 (6), pp. 852-834

Abstract
An analysis of results from published laboratory tests on Jossigny silt and Barcelona clayey silt is presented to confirm the existence of a unique capillary bonding function linking the quotient between unsaturated and saturated void ratio, at the same mean average skeleton stress, to a single capillary bonding scalar variable. The analysis confirms that the same capillary bonding function applies to both normally consolidated and critical stress states. The above two experimental sets with the addition of further published data for Speswhite Kaolin are also used to study the relationship between unsaturated critical shear strength, mean average skeleton stress and capillary bonding variable. The results of such analysis are assessed in the light of a similar modelling framework proposed in the literature.
Abstract
An analysis of results from published laboratory tests on Jossigny silt and Barcelona clayey silt is presented to confirm the existence of a unique capillary bonding function [...]
- 1
- read
A full-scale in situ heating test for high-level nuclear waste disposal: observations, analysis and interpretation
A. Gens, M. Sanchez, L. Guimarães, E. Alonso

Geotechnique (2009). Vol. 59 (4), pp. 377-399

Abstract
The paper describes the performance, observations and interpretation of a large-scale in situ heating test that simulates a disposal concept for heat-emitting, high-level nuclear waste. In the experiment, heaters are emplaced in the axis of a tunnel excavated in granite to simulate the heat production of radioactive waste. The test is fully instrumented, and attention is focused on the thermo-hydro-mechanical (THM) behaviour of the near-field region constituted by the compacted bentonite barrier surrounding the heater and the immediately adjacent rock. Interpretation of the test is assisted by the performance of a coupled numerical analysis based on a formulation that incorporates the relevant THM phenomena. Initial and boundary conditions for the analysis as well as material parameters are determined from an extensive programme of field and laboratory experiments. The paper presents and discusses the thermal, hydraulic and mechanical observations in the bentonite barrier and in the host rock. Special attention is paid to the progress of hydration in the barrier, to the effects of heating and vapour transport, and to the development of swelling pressures in the barrier. After five years of heating, one of the heaters was switched off and the experiment was partially dismantled, allowing the final state of the barrier to be observed directly. The numerical analysis performed has proved able to represent the progress of the experiment very satisfactorily. In addition, predictions concerning the final state of the clay barrier are very close to the observations obtained during dismantling. The performance and analysis of the in situ test have significantly enhanced the understanding of a complex THM problem and have proved the capability of the numerical formulation to provide adequate predictive capacity
Abstract
The paper describes the performance, observations and interpretation of a large-scale in situ heating test that simulates a disposal concept for heat-emitting, high-level [...]
- 1
- read
Performance of the Opalinus Clay under thermal loading: experimental results from Mont Terri rock laboratory (Switzerland)
A. Gens, K. Wieczorek, I. Gaus, B. Garitte, J. Mayor, K. Schuster, G. Armand, J. García-Siñeriz, T. Trick

Swiss Journal of Geosciences (2017). Vol. 110 (1), pp. 269-286

Abstract
The final publication is available at Springer via http://dx.doi.org/10.1007/s00015-016-0258-8 The paper presents an overview of the behaviour of Opalinus Clay under thermal loading as observed in three in situ heating tests performed in the Mont Terri rock laboratory: HE-B, HE-D and HE-E. The three tests are summarily described; they encompass a broad range of test layouts and experimental conditions. Afterwards, the following topics are examined: determination of thermal conductivity, thermally-induced pore pressure generation and thermally-induced mechanical effects. The mechanisms underlying pore pressure generation and dissipation are discussed in detail and the relationship between rock damage and thermal loading is examined using an additional in situ test: SE-H. The paper concludes with an evaluation of the various thermo-hydro-mechanical (THM) interactions identified in the heating tests.
Abstract
The final publication is available at Springer via http://dx.doi.org/10.1007/s00015-016-0258-8 The paper presents an overview of the behaviour of Opalinus Clay under thermal [...]
- 1
- read
Analysis of unsaturated materials hydration incorporating the effect of thermo-osmotic flow
M. Castilla, C. Arson, A. Gens, F. Aponte

Geomechanics for energy and the environment (2016). Vol. 6, pp. 101-115

Abstract
The geological disposal of a high level radioactive waste relies in a system composed of engineered and geological barriers. The soils and rocks involved in the design of this type of solution are generally initially unsaturated and subject to complex thermal, hydraulic and mechanical (THM) coupled phenomena triggered by the simultaneous heating and hydration of the barrier materials under confined conditions. Mathematical THM formulations are typically used to analyze the behavior and long term performance of the barriers system. These types of formulations generally do not include some coupled processes, for example thermo-osmosis (i.e. the movement of liquid water induced by gradient of temperature), because they are considered not significant when compared against the main or direct processes (e.g., Darcy’s, Fourier’s and Fick’s laws). In this work, the potential effects of thermo-osmotic phenomenon is studied in detail. Typical flow equations are modified to include thermo-osmotic flows and then they are implemented in numerical simulators. Two case studies are analyzed. The first one focuses on a simple and already proposed model to study the behavior of a geological barrier for nuclear waste when subjected to heating and hydration. The other case corresponds to the study of an engineered clay barrier material in the laboratory subjected to hydraulic and thermal gradients similar to the ones expected in real repository conditions. In both cases the analyses with and without thermo-osmotic flows are compared. From these comparisons it is observed that the effect of thermo-osmosis can be quite significant. Thermo-osmotic effects also assisted to explain the apparent low wetting observed in the hydration of a clayey barrier material.
Abstract
The geological disposal of a high level radioactive waste relies in a system composed of engineered and geological barriers. The soils and rocks involved in the design [...]
- 1
- read
A time-dependent anisotropic model for argillaceous rocks: application to an underground excavation in Callovo-Oxfordian claystone
M. Mánica, A. Gens, J. Vaunat, D. Ruiz

Computers and Geotechnics (2017). Vol. 85, pp. 341-350

Abstract
The paper presents a constitutive model for argillaceous rocks, developed within the framework of elastoplasticity, that includes a number of features that are relevant for a satisfactory description of their hydromechanical behaviour: anisotropy of strength and stiffness, behaviour nonlinearity and occurrence of plastic strains prior to peak strength, significant softening after peak, time-dependent creep deformations and permeability increase due to damage. Both saturated and unsaturated conditions are envisaged. The constitutive model is then applied to the simulation of triaxial and creep tests on Callovo-Oxfordian (COx) claystone. Although the main objective has been the simulation of the COx claystone behaviour, the model can be readily used for other argillaceous materials. The constitutive model developed is then applied, via a suitable coupled hydromechanical formulation, to the analysis of the excavation of a drift in the Meuse/Haute-Marne Underground Research Laboratory. The pattern of observed pore water pressures and displacements, as well as the shape and extent of the damaged zone, are generally satisfactorily reproduced. The relevance and importance of rock anisotropy and of the development of a damaged zone around the excavations are clearly demonstrated.
Abstract
The paper presents a constitutive model for argillaceous rocks, developed within the framework of elastoplasticity, that includes a number of features that are relevant for [...]
- 1
- read
Numerical analysis of suction embedded plate anchors in structured clay
T. Charlton, M. Rouainia, A. Gens

Applied Ocean Research (2016). Vol. 61, pp. 156-166

Abstract
As offshore energy developments move towards deeper water, moored floating production facilities are increasingly preferred to fixed structures. Anchoring systems are therefore of great interest to engineers working on deep water developments. Suction embedded plate anchors (SEPLAs) are rapidly becoming a popular solution, possessing a more accurate and predictable installation process compared to traditional alternatives. In this paper, finite element analysis has been conducted to evaluate the ultimate pullout capacity of SEPLAs in a range of post-keying configurations. Previous numerical studies of anchor pullout capacity have generally treated the soil as an elastic-perfectly plastic medium. However, the mechanical behaviour of natural clays is affected by inter-particle bonding, or structure, which cannot be accounted for using simple elasto-plastic models. Here, an advanced constitutive model formulated within the kinematic hardening framework is used to accurately predict the degradation of structure as an anchor embedded in a natural soft clay deposit is loaded to its pullout capacity. In comparison with an idealised, non-softening clay, the degradation of clay structure due to plastic strains in the soil mass results in a lower pullout capacity factor, a quantity commonly used in design, and a more complex load–displacement relationship. It can be concluded that clay structure has an important effect on the pullout behaviour of plate anchors.
Abstract
As offshore energy developments move towards deeper water, moored floating production facilities are increasingly preferred to fixed structures. Anchoring systems are therefore [...]
- 1
- read
Exploring ice content on partially saturated frozen soils using dielectric permittivity and bulk electrical conductivity measurements
Y. Mao, E. Romero, A. Gens

E3S Web of Conferences (2016). Vol. 9, pp. 1-9

Abstract
The present paper explores the use of the measurement of bulk electric conductivity and relative dielectric permittivity during freezing and thawing to estimate the ice content of two different partially saturated soils. The soils (Castelldefels fine sand and Barcelona clayey silt) were prepared at different degrees of saturation and dry densities at room temperature. Different target temperatures were used, which were reached at varying freezing rates and controlled with a thermal bath. Models were used to fit electrical conductivity and relative dielectric permittivity results under full unfrozen liquid and maximum ice conditions. The extension of these models allows estimating ice content on partially saturated soils at different porosities.
Abstract
The present paper explores the use of the measurement of bulk electric conductivity and relative dielectric permittivity during freezing and thawing to estimate the ice content [...]
- 1
- read
A numerical investigation of the incremental behavior of crushable granular soils
M. Cintia, M. Arroyo, F. Calvetti, A. Gens

International Journal for Numerical and Analytical Methods in Geomechanics (2016). Vol. 40 (13), pp. 1773-1798

Abstract
The mechanical behavior of granular materials is characterized by strong nonlinearity and irreversibility. These properties have been differently described by a variety of constitutive models. To test any constitutive model, experimental data relative to the nature of the incremental stress–strain response of the material is desirable. However, this type of laboratory data is scarce because of being expensive and difficult to obtain. The discrete element method has been used several times as an alternative to obtain incremental responses of granular materials. Crushable grains add one extra source of irreversibility to granular materials. Crushability has been variously incorporated into different constitutive models. Again, it will be helpful to obtain incremental responses of crushable granular materials to test these models, but the experimental difficulties are increased. Making use of a recently introduced crushing model for discrete element simulation, this paper presents a new procedure to obtain incremental responses in discrete analogs of granular crushable materials. The parallel probe approach, previously used for uncrushable discrete analogs, is here extended to account for the presence of crushable grains. The contribution of grain crushing to the incremental irreversible strain is identified and separately measured. Robustness of the proposed method is examined in detail, paying particular attention to aspects such as dynamic instability or crushing localization. The proposed procedure is later applied to map incremental responses of a discrete analog of Fontainebleau sand on the triaxial plane. The effect of stress ratio and granular state on plastic flow characteristics is highlighted.
Abstract
The mechanical behavior of granular materials is characterized by strong nonlinearity and irreversibility. These properties have been differently described by a variety of [...]
- 1
- read
Analysis of hydro-mechanical processes in a ventilated tunnel in an argillaceous rock on the basis of different modelling approaches
B. Garitte, A. Bond, A. Millard, C. Zhang, C. McDermott, S. Nakama, A. Gens

Journal of rock mechanics and geotechnical engineering (2013). Vol. 5 (1), pp. 1-17

Abstract
In this paper, a modelling benchmark exercise from the DECOVALEX-2011 project is presented. The benchmark is based on the performance and results of a laboratory drying test and of the ventilation experiment (VE) carried out in the Mont Terri Underground Rock Laboratory (URL). Both tests involve Opalinus clay. The work aims at the identification, understanding and quantification of mechanisms taking place during the ventilation of a gallery in argillaceous host rocks on one hand and at investigating the capacity of different codes and individuals to reproduce these processes on the other hand. The 4-year in situ VE took place in a 1.3 m diameter unlined tunnel and included two resaturation–desaturation cycles. The test area was equipped with over one hundred sensors (including the global water mass balance of the system, relative humidity (RH), water content, liquid pressure, relative displacement and concentration of some chemical species) to monitor the rock behaviour during ventilation. The laboratory drying experiment, carried out before the VE, was designed to mimic the in situ conditions. The work was organized in a progressive manner in terms of complexity of the computations to be performed, geared towards the full hydro-mechano-chemical (HMC) understanding of the VE, the final objective. The main results from the modelling work reported herein are that the response of the host rock to ventilation in argillaceous rocks is mainly governed by hydraulic processes (advective Darcy flow and non-advective vapour diffusion) and that the hydro-mechanical (TM) back coupling is weak. A ventilation experiment may thus be regarded as a large scale-long time pump test and it is used to determine the hydraulic conductivity of the rock mass.
Abstract
In this paper, a modelling benchmark exercise from the DECOVALEX-2011 project is presented. The benchmark is based on the performance and results of a laboratory drying [...]
- 1
- read
A chemo-mechanical constitutive model accounting for cation exchange in expansive clays
L. Guimarães, A. Gens, M. Sanchez, S. Olivella

Geotechnique (2013). Vol. 63 (3), pp. 221-234

Abstract
The paper presents a chemo-mechanical model for expansive clays that takes into account the effects of cation content and cation exchange. These factors play a key role in the mechanical behaviour of very active clays, particularly with regard to volumetric behaviour. The model is based on an existing double-structure formulation that distinguishes specifically between microstructure and macrostructure. Chemical effects are defined at the microstructural level, the seat of the basic physico-chemical phenomena affecting highly swelling clays. The microstructural model accounts for changes in both osmotic suction and in cation content. Microstructural strains are considered to be reversible; material irreversibility arises from the interaction between the two structural levels. The formulation is developed for general unsaturated conditions; saturation is considered as a limiting case. The model is successfully applied to the reproduction of experimental behaviour observed in oedometer tests on saturated bentonite subjected to chemo-mechanical loadings, and in hydration tests of unsaturated bentonite performed using different solute concentrations.
Abstract
The paper presents a chemo-mechanical model for expansive clays that takes into account the effects of cation content and cation exchange. These factors play a key role [...]
- 1
- read
Diseño hidráulico de aliviaderos escalonados en presas de HCR
A. Amador, M. Juny, J. Dolz

Ingeniería del agua (2006). Vol. 13 (4), pp. 289-302

Abstract
En el presente artículo se presenta un conjunto de criterios para el diseño de aliviaderos escalonados con pendientes típicas de presas de hormigón compactado con rodillo. El texto se basa en Información recogida en la bibliografía e incorpora los resultados del trabajo de Investigación desarrollado en Amador (2005). Se aborda el diseño de la cresta, la selección del ancho del aliviadero y la geometría de los peldaños. Se proponen criterios para determinar el tipo de flujo existente sobre la estructura y, en el caso del flujo rasante, se presentan expresiones que permiten obtener las principales características del flujo a lo largo de la rápida. Con ha.se en los resultados del análisis del campo de presiones se proponen un conjunto de ecuaciones para estimar las solicitaciones que el vertido ejerce sobre los peldaños a lo largo del aliviadero. Finalmente se hacen algunas consideraciones sobre los aspectos constructivos de los aliviaderos escalonados.
Abstract
En el presente artículo se presenta un conjunto de criterios para el diseño de aliviaderos escalonados con pendientes típicas de presas de hormigón [...]
- 1
- read
Thrust and torque components on mixed-face EPB drives
C. González, M. Arroyo, A. Gens

Tunnelling and Underground Space Technology (2016). Vol. 57, pp. 47-54

Abstract
In this communication we propose a method to estimate net thrust and torque applied at the excavation front by cutting tools from EPB machines when they are working in mixed faces constituted by soils and soft rock. The method is inspired by similar simplifications used for the analysis of TBM drives in rock. The proposal is validated using a database of EPB registers which were gathered from more than 35 km of tunnel drives excavated in soils, soft rock and heterogeneous media. The results allow us to assess the influence of the type of ground excavated and its geotechnical properties on the net thrust and torque applied.
Abstract
In this communication we propose a method to estimate net thrust and torque applied at the excavation front by cutting tools from EPB machines when they are working in mixed [...]
- 0
- read
Wear and abrasivity: observations from EPB drives in mixed soft – rock sections
C. González, M. Arroyo, A. Gens

Geomechanik and Tunnelbau (2015). Vol. 8 (3), pp. 258-264

Abstract
This paper summarizes the main observations related to geotechnical properties and tool changes that characterize the different tunnel drives in a database of 33 km of EPB tunnel records from the Barcelona area. The data have been examined in detail with regard to cutting tool replacement and performance of the mechanized excavation. The database includes tunnels in soft soils, in hard and medium rocks and in mixed soil‐rock conditions; tool changing records and geotechnical properties. Transverse and longitudinal geotechnical heterogeneity are accounted for systematically. Longitudinal heterogeneity is used to subdivide the drives in the database into homogeneous units. Transverse (within section) heterogeneity is described by a set of newly developed impact factors FI.
Abstract
This paper summarizes the main observations related to geotechnical properties and tool changes that characterize the different tunnel drives in a database of 33 km of EPB [...]
- 0
- read
Abrasividad y su influencia en el rendimiento de una excavación mecanizada
C. González, M. Arroyo, A. Gens

Obras y proyectos. Revista de ingeniería civil (2013). Vol. 13, pp. 6-18

Abstract
El empleo de tuneladoras TBM (Tunnel Boring Machine) es cada vez más frecuente aunque su optimización requiere la evaluación precisa de varios riesgos geotécnicos entre ellos, el efecto de la abrasividad del suelo en el coste y planificación de un proyecto dado. El desgaste de las herramientas es más difícil de calcular que el resto de parámetros de la maquinaria, debido a la complejidad de la interacción entre herramienta de corte y terreno. En este trabajo se usan datos de un caso real de túnel en terrenos mixtos suelo-roca para examinar el resultado de varias metodologías de predicción de la penetración de TBM. También se examinan algunas predicciones de desgaste y se describe y aplica un nuevo método para la evaluación de la abrasividad de geomateriales que puede aplicarse tanto a materiales sueltos como a rocas.
Abstract
El empleo de tuneladoras TBM (Tunnel Boring Machine) es cada vez más frecuente aunque su optimización requiere la evaluación precisa de varios riesgos [...]
- 0
- read
Modelling fluid deformable surfaces with an emphasis on biological interfaces
A. Torres-Sánchez, D. Millán, M. Arroyo

Journal of fluid mechanics (2019). Vol. 872, pp. 218-271 (Preprint)

Abstract
Fluid deformable surfaces are ubiquitous in cell and tissue biology, including lipid bilayers, the actomyosin cortex or epithelial cell sheets. These interfaces exhibit a complex interplay between elasticity, low Reynolds number interfacial hydrodynamics, chemistry and geometry, and govern important biological processes such as cellular traffic, division, migration or tissue morphogenesis. To address the modelling challenges posed by this class of problems, in which interfacial phenomena tightly interact with the shape and dynamics of the surface, we develop a general continuum mechanics and computational framework for fluid deformable surfaces. The dual solid–fluid nature of fluid deformable surfaces challenges classical Lagrangian or Eulerian descriptions of deforming bodies. Here, we extend the notion of arbitrarily Lagrangian–Eulerian (ALE) formulations, well-established for bulk media, to deforming surfaces. To systematically develop models for fluid deformable surfaces, which consistently treat all couplings between fields and geometry, we follow a nonlinear Onsager formalism according to which the dynamics minimizes a Rayleighian functional where dissipation, power input and energy release rate compete. Finally, we propose new computational methods, which build on Onsager’s formalism and our ALE formulation, to deal with the resulting stiff system of higher-order partial differential equations. We apply our theoretical and computational methodology to classical models for lipid bilayers and the cell cortex. The methods developed here allow us to formulate/simulate these models in their full three-dimensional generality, accounting for finite curvatures and finite shape changes. This article has been published in a revised form in Journal of fluid mechanics,
Abstract
Fluid deformable surfaces are ubiquitous in cell and tissue biology, including lipid bilayers, the actomyosin cortex or epithelial cell sheets. These interfaces exhibit a [...]
- 0
- read
A FIC‐based stabilized mixed finite element method with equal order interpolation for solid–pore fluid interaction problems
I. de-Pouplana, E. Oñate

Int. J. Numer. Anal. Meth. Geomech. (2017). Vol. 41 (1), pp. 110-134

Abstract
A new mixed displacement‐pressure element for solving solid–pore fluid interaction problems is presented. In the resulting coupled system of equations, the balance of momentum equation remains unaltered, while the mass balance equation for the pore fluid is stabilized with the inclusion of higher‐order terms multiplied by arbitrary dimensions in space, following the finite calculus (FIC) procedure. The stabilized FIC‐FEM formulation can be applied to any kind of interpolation for the displacements and the pressure, but in this work, we have used linear elements of equal order interpolation for both set of unknowns. Examples in 2D and 3D are presented to illustrate the accuracy of the stabilized formulation for solid–pore fluid interaction problems.
Abstract
A new mixed displacement‐pressure element for solving solid–pore fluid interaction problems is presented. In the resulting coupled system of equations, the balance [...]
- 0
- read

information

About this publication

How to submit

Open access

Contact