Documents published in 2020 : Scipedia

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 [...]
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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 [...]
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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 [...]
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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 [...]
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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 [...]
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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
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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 [...]
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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 [...]
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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. [...]
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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 [...]
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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 [...]
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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 [...]
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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 [...]
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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 [...]
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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, [...]
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Unsaturated soils: models algorithm and applications
A. Gens, D. Sloan

Computers and Geotechnics (2008). Vol. 35 (6), pp. 809
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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 [...]
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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 [...]
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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
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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 [...]
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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 [...]
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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 [...]
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Behaviour of a bentonite barrier in the laboratory: experimental results up to 8 years and numerical simulation
M. Villar, M. Sanchez, A. Gens

Physics and Chemistry of the Earth (2008). Vol. 33 (S1), pp. S476-S485

Abstract
The conditions of the bentonite in an engineered barrier for high-level radioactive waste disposal were simulated in a series of tests performed in cylindrical cells (length 60 cm, diameter 7 cm). Inside the cells, six blocks of FEBEX bentonite compacted to dry density 1.65 g/cm3 were piled up, giving rise to a total length similar to the thickness of the clay barrier in a repository according to the Spanish concept. The bottom surface of the material was heated at 100 °C and the top surface was injected with granitic water. The duration of the tests was 6, 12, 24 and 92 months. The temperatures inside the clay and the water intake were measured during the tests and, at the end, the cells were dismounted and the dry density, water content and hydro-mechanical properties were measured at different positions. The injection of water provokes, near the hydration surface, a decrease of the dry density due to the increase of the water content and the clay swelling, while heating gives rise to an increase of the dry density and a reduction of the water content in the hottest areas. A fully coupled thermo-hydro-mechanical (THM) formulation has been adopted as a general framework to analyse these experiments. This work presents the comparisons between the variables recorded online during the tests (water intake and temperature) and the model results. The main results of the postmortem analysis (water content and dry density) are also modelled.
Abstract
The conditions of the bentonite in an engineered barrier for high-level radioactive waste disposal were simulated in a series of tests performed in cylindrical cells (length [...]
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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, [...]
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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 [...]
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Determinación de la masa modal en estructuras civiles mediante el acoplamiento de un sistema dinámico oscilante en la situación de amortiguamiento proporcional independiente de la frecuencia
L. VILLA GARCIA

Rev. int. métodos numér. cálc. diseño ing. (2020). Vol. 36, (3), 43

Abstract
A new alternative is presented for the estimation of modal mass, in order to scale the vibration modes obtained from operational modal analysis tests, using optimization techniques, in the frequency-independent proportional damping situation (structural or hysteretic), achieving optimal results even with the presence of a high level of noise in the signal. After a brief exposition of the theoretical foundations, and the limitations in the current state of the art, the determination of modal parameters is analyzed in a coupled dynamic system, using optimization techniques. To illustrate the procedure, two examples of application are presented: first, for the case of an elementary beam model of small dimensions; and then, to confirm the capacity of the proposed method to be applied to real civil structures, said capacity is illustrated by a numerical simulation, on a very slender bridge currently in service, and with a very complex internal geometry of its main beam.
Abstract
A new alternative is presented for the estimation of modal mass, in order to scale the vibration modes obtained from operational modal analysis tests, using optimization techniques, [...]
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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 [...]
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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 [...]
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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 [...]
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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 [...]
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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 [...]
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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 [...]
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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. [...]
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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 [...]
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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) [...]
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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 [...]
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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 [...]
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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 [...]
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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 [...]
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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. [...]
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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. [...]
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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 [...]
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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 [...]
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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 [...]
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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 [...]
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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. [...]
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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 [...]
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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 [...]
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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 [...]
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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. [...]
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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 [...]
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Artificial neural network to estimate an index of water quality
L. Quiñones Huatangari, L. Ochoa Toledo, N. Kemper Valverde, O. Gamarra Torres, J. Bazán Correa, J. Delgado Soto

Enfoque UTE - Scientific Engineering Journal (2020). Vol. 11, (2), 40

Abstract
The artificial neural network (RNA) is a computational model that emulates the biological neural system in information processing. The originating models are suitable for the purpose of describing long-term specifics, in addition to nonlinear relationships. This tool is used to predict physical chemical and microbiological parameters that influence water quality. The United States National Sanitation Foundation proposed a water quality index, known as the NSF WQI. This article describes the design, training and use of the three-layer neural perceptron neural model for the calculation of the NSF WQI of the Utcubamba River and its tributaries. Using the Matlab software and applying the Levenberg-Marquardt training algorithm, the optimal RNA architecture was found to be 6-12-1, plus the percentage for the training, validation, and test sets of 70 %, 10 %, and 20 % respectively. RNA performance has been evaluated using the root of the root mean square error (RMSE) and the correlation coefficient (R). High correlations (greater than 0.94) were made between the measured and predicted values. Finally, the RNA proposal offers a useful alternative for the calculation and prediction of the water quality index in relation to dissolved oxygen (DO), biochemical demand for oxygen (BOD), nitrates, fecal coliforms, potential for hydrogen ions (pH) and turbidity.
Abstract
The artificial neural network (RNA) is a computational model that emulates the biological neural system in information processing. The originating models are suitable for [...]
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Third-party management in software development: proposal of a methodology
Y. Núñez-Sánchez, A. González-Torres

Enfoque UTE - Scientific Engineering Journal (2020). Vol. 11, (2), 38

Abstract
Outsourcing allows organizations to reduce costs, optimize the use of resources, provide added value in services and goods, and concentrate on achieving the strategic objectives of the business. However, many software projects have failed due to the lack of knowledge of the factors involved in its planning. Some of these elements are poor communication with the supplier, weak monitoring of the status of tasks, lack of active participation of users and stakeholders at all stages of the process, and software quality assurance. Consequently, this research aims to aid the management of the outsourcing process and proposes a methodology for its management during system development. The methodology comprises 7 phases, each one with its inputs, tasks, and outputs, which are used by the following stages. In summary, it synthesizes the best practices for the management of third parties.
Abstract
Outsourcing allows organizations to reduce costs, optimize the use of resources, provide added value in services and goods, and concentrate on achieving the strategic objectives [...]
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CFD Analysis of a solar flat plate collector with different cross sections
A. Andrade Cando, W. Quitiaquez Sarzosa, L. Toapanta

Enfoque UTE - Scientific Engineering Journal (2020). Vol. 11, (2), 36

Abstract
Low and medium solar heating systems used for domestic and industrial applications, such as water and space heating, usually utilize solar flat plate collectors in order to absorb solar thermal energy converting it into heat and then transferring the heat to a fluid (usually water or air) that flows through it. The aim of this study is to evaluate the solar flat plate collector’s efficiency and the fluid behavior inside the pipeline with three different cross sections, whose hydraulic diameters are 10, 5.12 and 6.16 mm, by using ANSYS Fluent. The results obtained from the Computational Fluid Dynamics (CFD) tool showed that the collector with the Type I cross section reached temperatures up to 330 K at the pipe outlet obtaining an efficiency of 68 %, higher than those of Types II and III, whose efficiencies were 51 % and 60 %, respectively. Type I cross section also presented the lowest values in both speed and pressure drop, these being 0.266 m/s and 108.3 Pa, respectively.
Abstract
Low and medium solar heating systems used for domestic and industrial applications, such as water and space heating, usually utilize solar flat plate collectors in order to [...]
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Optimal Location of Transformers in Electrical Distribution Networks Using Geographic Information Systems
S. Pinzón, S. Yánez, M. Ruiz

Enfoque UTE - Scientific Engineering Journal (2020). Vol. 11, (1), 34

Abstract
This research shows a heuristic model for the design of scalable and reliable electrical distribution networks. The algorithms presented allow to optimize the location of transformation centers using on their database geographic information systems from which it is possible to define user locations, candidate sites, possible routes for the deployment of the electricity grid and, in general, data for the reconstruction of the scenario. The model employs clustering and triangulation methods, as well as algorithms for creating a minimally expanding tree and the consequent site assignment for transformer placement. After setting the optimal locations for the transformer site, the algorithms compute voltage drops in secondary circuits, required transformation capability, execution times, and coverage achieved. The results obtained are adjusted to the requirements of an actual distribution power grid and show a good performance on the proposed scenario.
Abstract
This research shows a heuristic model for the design of scalable and reliable electrical distribution networks. The algorithms presented allow to optimize the location of [...]
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Alternative Under Frecuency Load Disconection Methodology Based on Semi-Adaptative Model
D. Carrión, A. Ayo, J. González

Enfoque UTE - Scientific Engineering Journal (2020). Vol. 11, (1), 32

Abstract
Stability analysis in electrical power systems is based on the study in dynamic state of the voltage and frequency, since at the moment that there is some contingency it fluctuates drastically due to the primary and secondary controls of the voltage and frequency to the power systems that act on the generators. In order to solve the possible stability problems that may arise in power systems, various techniques have been developed that act on the generating machines for their protection as well as on the loads for the power cut. The present investigation proposes an alternative methodology for load disconnection by low frequency as an option to save the power system from a possible blackout due to instability due to a fall in the frequency, managing to improve the results affected by other improved techniques, the frequency change range, frequency deviation and the effects of demand disconnection. The proposed methodology was tested in the IEEE 14 bus system.
Abstract
Stability analysis in electrical power systems is based on the study in dynamic state of the voltage and frequency, since at the moment that there is some contingency it fluctuates [...]
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Outlier detection with data mining techniques and statistical methods
M. Orellana Cordero, P. Cedillo

Enfoque UTE - Scientific Engineering Journal (2020). Vol. 11, (1), 30

Abstract
The detection of outliers in the field of data mining (DM) and the process of knowledge discovery in databases (KDD) is of great interest in areas that require support systems for decision making. A straightforward application can be found in the financial area, where DM can potentially detect financial fraud or find errors produced by the users. Thus, it is essential to evaluate the veracity of the information, through the use of methods for the detection of unusual behaviors in the data. This paper proposes a method to detect values that are considered outliers in a database of nominal type data. The method implements a global algorithm of "k" closest neighbors, a clustering algorithm called k-means and a statistical method called chi-square. These techniques have been implemented on a database of clients who have requested a financial credit. The experiment was performed on a data set with 1180 tuples, where, outliers were deliberately introduced. The results showed that the proposed method is able to detect all the outliers entered.
Abstract
The detection of outliers in the field of data mining (DM) and the process of knowledge discovery in databases (KDD) is of great interest in areas that require support systems [...]
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Estimated cost of electricity with time horizon for micro grids based on the policy response of demand for real price of energy
E. GARCIA TORRES

Enfoque UTE - Scientific Engineering Journal (2020). Vol. 11, (1), 28

Abstract
The intelligent microgrids are an efficient alternative, which allows to supply the demand decreasing the losses of the electrical system and at the same time; the environment and the consumers are the main beneficiaries. This article develops a heuristic based on an energy management model based on the real price of electricity, which will allow end users to encourage the implementation of a policy of response to demand, in order to optimize their consumption, for which a micro smart grid is analyzed, with conventional and non-conventional renewable generation, In addition, a mechanism of "real energy price" will be implemented as a policy of response to demand, with the aim of optimizing the costs of energy that will be transferred to users depending on the stratum to which it belongs, these costs will have a short-term horizon with hourly intervals, achieving a reduction in the purchase of energy from the system
Abstract
The intelligent microgrids are an efficient alternative, which allows to supply the demand decreasing the losses of the electrical system and at the same time; the environment [...]
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Novel Approach for Teaching English Language using Emerging Information and Communication Technologies for Visual Impairment Students
J. Cardenas, E. Inga

Enfoque UTE - Scientific Engineering Journal (2020). Vol. 11, (1), 26

Abstract
Nowadays, Higher Education Institutions (HEI) need to be more inclusive from the methodological vision appropriate used in the classroom. Visual impairment students (VIS) become a challenge for teachers who look for incorporating different learning environments. This challenge increases when teaching and learning process to VIS is related to the English language; due to the absence of educational didactic resources available at the school and the lack of knowledge of appropriate teaching methodologies and strategies to develop the different language skills: listening, speaking, reading and writing that go with the educational process in the acquisition of the English language. In accordance with this problem, this research proposes a novel methodological strategy, based on the usage of meaningful learning with emerging technologies as a main guide for students with visual impairment. Thus, the road map of good practices in the use of this methodology will allow establishing a clear process to achieve students’ active, meaningful and autonomous participation, using the least time in the teaching-learning process of the English language.
Abstract
Nowadays, Higher Education Institutions (HEI) need to be more inclusive from the methodological vision appropriate used in the classroom. Visual impairment students (VIS) [...]
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Evaluation of video traffic behavior metrics in an experimental multicast network
H. Facchini, S. Pérez, A. Dantiacq, F. Hidalgo

Enfoque UTE - Scientific Engineering Journal (2020). Vol. 11, (1), 24

Abstract
Currently, there is a significant change in data traffic on networks, both local and Internet, across the spectrum of possible customers, whether fixed or mobile. The consumption of video traffic increases day by day in all its formats. Service providers are required more bandwidth, quality and performance, for all products, but mainly those based on video. This article presents an improved version of our laboratory tests for generic networks with four sub-scenarios, which allow injecting multicast video traffic, represented in different codecs. The topology of network used includes a streaming server and up to 20 desktop computers as clients. The most important metrics to be analyzed have been defined, based on performance and quality of service (QoS) measurements under limited bandwidth conditions. Experimental numerical results can be useful for administrators, simulation analysts, designers, and data network planners. But, also, this document aims to serve as a guide for the management of similar networks and the efficiently use available resources, without compromising performance and QoS.
Abstract
Currently, there is a significant change in data traffic on networks, both local and Internet, across the spectrum of possible customers, whether fixed or mobile. The consumption [...]
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In-situ co-design of Mobile Games using Design Thinking’s resources approach
C. Challiol, F. Borrelli, F. Goin Plexevi, C. Rouaux Servat, F. Mendiburu, E. Gomez-Torres, S. Gordillo

Enfoque UTE - Scientific Engineering Journal (2020). Vol. 11, (1), 22

Abstract
The contribution of this paper is to explore how in-situ co-design of indoor spaces (e.g. building) of Location-based Mobile Games could be handle, by describing the learned lessons on this topic. This paper presents a conceptual framework for in-situ co-design of indoor spaces on Location-based Mobile Games to assist to carry out this kind of experience using useful resources (as Design Thinking's resources). An experience of in-situ co-design for an indoor space on a Location-based Mobile Game is presented using this framework; for some phases an authoring tool was used which allows in-situ co-design of relevant locations for an application. Based on this experience, the authoring tool was extended to create a specific kind of Location-based Mobile Game. This paper presents this extension along with a proof of concept that shows how an in-situ co-designed game created by this extension was used by end-users.
Abstract
The contribution of this paper is to explore how in-situ co-design of indoor spaces (e.g. building) of Location-based Mobile Games could be handle, by describing the learned [...]
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Review of the state of art of DX-SAHP systems to obtain domestic hot water
W. Quitiaquez, I. Simbaña, C. Isaza-Roldán, P. Quitiaquez, C. Nieto-Londoño, F. Toapanta-Ramos

Enfoque UTE - Scientific Engineering Journal (2020). Vol. 11, (2), 20

Abstract
The investigation purpose is to elaborate a detailed review about previous published investigations with direct-expansion solar-assisted heat pumps (DX-SAHP) used for water heating, in the last years. The growing energy consumption, the using of refrigerants that weaken the ozone layer, the greenhouse gases emission to the atmosphere and the global warming effect are the main problems that the conventional water heating systems present. Using hydrocarbons as refrigerants represents a pollution reduction and it is also the best option to replace hydrochlorofluorocarbons and chlorofluorocarbons, due to their low values of global warming potential and ozone depletion potential, close to 0. A DX-SAHP system takes advantage of the thermal solar energy directly by using a bare flat-plate solar collector. These systems provide domestic hot water over 50 °C and heating water volumes until 200 liters reaching COP values higher than 4. Solar energy and the using of alternative refrigerants with a low environmental impact are proposed to reach this purpose.
Abstract
The investigation purpose is to elaborate a detailed review about previous published investigations with direct-expansion solar-assisted heat pumps (DX-SAHP) used for water [...]
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Design, evaluation and validation of an effluent treatment system for the leather tanning process: case Pieles del Sur E.I.R.L.
V. Muñoz Paz, V. Longa Cuayla, A. Carreño Arispe, J. Aguilar Franco

Enfoque UTE - Scientific Engineering Journal (2020). Vol. 11, (2), 18

Abstract
In this project a treatment system for the effluents of a leather tanning process was designed. This system was evaluated based on laboratory tests to ensure its viability, and the treatment was validated by analyzing effluents from the plant already installed. The system has three units: the first one is a Pretreatment that allows the oxidation of sulphides for the liming and draught baths, as well as the precipitation of chromium for the leather tanning baths; the second one is a Physical-Chemical Treatment for the general effluents of the process that allows to obtain treated effluents and decanted solids; the third is a sludge treatment that allows to obtain conditioned and low volume sludge to be collected for final disposal. The analysis of treated effluents showed a considerable reduction in the concentration of polluting chemicals that allows reusing the water and brings the company closer to compliance with the maximum levels allowed.
Abstract
In this project a treatment system for the effluents of a leather tanning process was designed. This system was evaluated based on laboratory tests to ensure its viability, [...]
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Evaluation of the efficiency of three oil extraction equipments with different oil palm genotypes (Elaeis sp.)
M. Navarrete Párraga, S. Zambrano Marcillo, W. Zambrano Sabando, M. Romero Pizarro, M. Racines Jaramillo, E. Paredes Puga, L. Quintero Roman, D. Ortega Cedillo

Enfoque UTE - Scientific Engineering Journal (2020). Vol. 11, (2), 16

Abstract
This work was performed in the oil extraction laboratory of the African Palm Program, of the Experimental Station “Santo Domingo” of the INIAP. The main objective was to determine the efficiency of three oil extraction equipments, in three oil palm genotypes. The equipments used were Velp solvent extractor, Soxhlet extractor and a 1500 psi hydraulic press. The genotypes evaluated are part of the germplasm bank of the Palm Program at INIAP: Elaeis guineensis (african palm), Elaeis oleifera (american palm) and E. oleifera x E. guineensis (interspecific hybrid). The experimental design was a complete random design (DCA), with 20 observations, followed by student’s test and Tukey test at a 5 significance, to determine differences between treatment means. The results showed highly significant differences between the different factors evaluated. The higher percentage of oil per bunch was obtained with the genotype E. guineensis in the Soxhlet extractor (18.43 %) and the lowest percentage for E. oleifera with the hydraulic press (0.34 %). The analysis of costs determined that the lowest cost was obtained with the hydraulic press with USD 8,20 per sample.
Abstract
This work was performed in the oil extraction laboratory of the African Palm Program, of the Experimental Station “Santo Domingo” of the INIAP. The main objective was [...]
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In situ morphological characterization of soursop (Annona muricata L.) plants in Manabí, Ecuador
R. Moreira Macías, H. Rodríguez, E. Héctor-Ardisana, C. Feicán-Mejía, S. Mestanza Velasco, W. Viera Arroyo

Enfoque UTE - Scientific Engineering Journal (2020). Vol. 11, (2), 14

Abstract
Soursop (Annona muricata L.) germplasm, from the central region of the Ecuadorian littoral, has diverse phenotypic characteristics, which have been little studied. The main objective of this research was to characterize in situ the morphological variability of 60 accessions of soursop. The morphological traits were evaluated using 20 quantitative and 10 qualitative variables of the plant and the fruit. Multivariate statistical methods were used as principal components, hierarchical conglomerate aggregation, discriminant and correlation analysis (Pearson) were performed. Descriptive analysis such as central tendency and dispersion (coefficient of variation, range, mean and standard deviation) were determined for the quantitative data; while frequencies were calculated for qualitative data. In terms of morphological traits, 74 % of the total variability was explained by the fourth component. Three conglomerates of similarity were formed, in which the height, diameter of canopy and fruit number per tree, were the characters of greater contribution for its conformation.
Abstract
Soursop (Annona muricata L.) germplasm, from the central region of the Ecuadorian littoral, has diverse phenotypic characteristics, which have been little studied. The main [...]
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Passion fruit oil (Passiflora edulis): Use of the seeds in cosmetic products
J. Proaño Bastidas, E. Rivadeneira, P. Moncayo, E. Mosquera

Enfoque UTE - Scientific Engineering Journal (2020). Vol. 11, (1), 12

Abstract
The work documented in this essay is focused on harnessing the properties of Passion fruit seeds Passiflora edulis f.flavicarpa Deg to achieve the design of a cosmetic product: an exfoliating cream containing passion fruit seed oil and solid residue generated from oil extraction. The applied methodology for the formulation of the cream was initially based on a combination of a mechanical process through pressing, and oil extraction from the seeds by the use of organic solvents, ethyl ether. The physicochemical analysis variables evaluated in the exfoliating cream were pH, extensibility and emulsion capacity. The physical properties were considered as listed, colour, odour, brightness and grittiness. Furthermore, the absence of lumps was evaluated as macroscopic indicators of adequate particle size distribution and uniform texture. It was concluded that the oil from passionfruit seeds due to its composition in protein and liquid elements, optimally conserves the inherent properties of a product designed for skincare and conditioning. The use of solid residue that for primary industries is considered as unstable waste, represents an innovative alternative in the range of available semi-finished raw materials with properties capable of enhancing the products for human consumption.
Abstract
The work documented in this essay is focused on harnessing the properties of Passion fruit seeds Passiflora edulis f.flavicarpa Deg to achieve the design of a cosmetic product: [...]
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Morphological, phenological and pomological differentiation of commercial cultivars of blackberry (Rubus glaucus Benth)
M. Iza, P. Viteri, M. Hinojosa, A. Martínez, A. Sotomayor Correa, W. Viera

Enfoque UTE - Scientific Engineering Journal (2020). Vol. 11, (2), 10

Abstract
The genus Rubus is one of the most diverse in terms of morphology and genetics, presenting a wide spectrum of wild and cultivated species that are desired by their edible fruits. In Ecuador, the cultivation of blackberry (R. glaucus and Rubus sp.) is present along the Inter-Andean region, grown between 2000 and 3100 masl. This fruit crop is economically important for its high demand for fresh and processed consumption. This research was carried out in the Tumbaco Experimental Farm of INIAP (Ecuador) with the objective of finding characters that allow the morphological, phenological and pomological differentiation of four blackberry cultivars (Castilla, Andimora, Colombiana and Brazos). The multivariate analysis showed three conglomerates (C). Cultivars Andimora and Colombiana (C3) do not have spines unlike Castilla (C2) and Brazos (C1). Colombian was the earliest cultivar (161 days of sprouting to harvest) and Castilla the latest (186 days). Brazos cultivar showed the highest fruit weight (5.85 g). Andimora reached the highest content of soluble solids (11.86 ºBrix) and had firm fruits. The differentiating characters observed in this study make possible to establish parameters of distinction between the cultivars that are currently cultivated in Ecuador.
Abstract
The genus Rubus is one of the most diverse in terms of morphology and genetics, presenting a wide spectrum of wild and cultivated species that are desired by their edible [...]
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Technological alternatives for the control of Botrytis sp. In Andean blackberry (Rubus glaucus)
M. Acosta Ruales, W. Viera, T. Jackson, W. Vásquez Castillo

Enfoque UTE - Scientific Engineering Journal (2020). Vol. 11, (2), 8

Abstract
The Andean blackberry crop (Rubus glaucus) is very important for the farmers, since they must implement cultural practices that allow reducing the use of synthetic pesticides. The objective of the study was to evaluate the effect of different technological alternatives for the control of Botrytis sp. in the blackberry crop. The treatments were: 1: Absolute control (silwet+water), 2: Traditional chemical treatment (Carbendazim), 3: Mirtaceae extract (Iridium®), 4: Bacterial metabolite (Balus®) and 5: Trichoderma spp. (Tricomix®). The applications were carried out every 15 days for the synthetic product and every 8 days for the biologicals, organic and the control. A randomized complete block design (RCBD) was used with 3 repetitions and Tukey test at 5 % were made. The studied variables were botrytis incidence (%), yield (g/plot), weight (g), polar and equatorial diameter (mm), firmness (N), total soluble solids (Brix), titratable acidity (% citric acid) and pH (log H+). Throughout a weekly incidence analysis, it was possibly to identify that the Carbendazim, Trichoderma spp. and mirtaceae extract had a better control in the incidence of Botrytis sp. in the blackberry fruit.
Abstract
The Andean blackberry crop (Rubus glaucus) is very important for the farmers, since they must implement cultural practices that allow reducing the use of synthetic pesticides. [...]
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Effect of neem on Phyllocnistis citrella Stainton and its parasitoid Ageniaspis citricola Logvinovskaya in Ecuador
E. Cañarte-Bermúdez, B. Navarrete-Cedeño, S. Montero-Cedeño, H. Arredondo-Bernal, O. Chávez-López, N. Bautista-Martínez

Enfoque UTE - Scientific Engineering Journal (2020). Vol. 11, (2), 6

Abstract
Efficacy of neem on Citrus Leafminer (CLM) and effect on its parasitoid Ageniaspis citricola was evaluated, using field, cage and olfactometer tests. Treatments were: aqueous extract of neem (50 gL-1), formulated oil of neem (10 mL L-1) and control. Field study was done in a Citrus aurantifolia orchard, three applications were carried out, which were evaluated every 48 hours until ten days after the treatment. Cage and olfactometer tests were performed in a greenhouse and repeated twice each time. In the cage, it were used 50 infested Citrus reticulata plants per experimental unit, while for the olfactometer test, as experimental arena, transparent plastic jars with 20 adults of CLM inside were used. Variables evaluated were: CLM infestation, dead, live and predated larvae, pupae, emerged adults and parasitized pupal chambers. The highest mortality of the CLM was caused by the aqueous extract of neem with 77.17%, which began 48 hours after application, suggesting inhibition of feeding. The aqueous extract of neem showed in average 88.80 % of repellency of adults of CLM and neem oil 85.64%. The high mortality of CLM and the repellent effect of neem, seem to influence negatively in parasitism which fluctuated between 9.45 % and 20.16 % in treated trees.
Abstract
Efficacy of neem on Citrus Leafminer (CLM) and effect on its parasitoid Ageniaspis citricola was evaluated, using field, cage and olfactometer tests. Treatments were: aqueous [...]
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Impact of Ecodriving on fuel emissions and consumption on road of Quito
J. Leguísamo Milla, E. Llanes Cedeño, J. Rocha Hoyos

Enfoque UTE - Scientific Engineering Journal (2020). Vol. 11, (1), 4

Abstract
This article presents the results of the impact of ecodriving on fuel consumption and the emission factors of polluting gases from a gasoline vehicle when performing road testing in the city of Quito, located at 2 810 meters above sea level. A route with traffic validated by the Technology Transfer Center has been selected for the training and investigation of vehicle emission control. A Chevrolet Aveo Family was used as a test vehicle, , considering is the bestselling vehicle in the city at the moment. And the equipment used to measure fuel consumption and the concentration of emissions was an onboard gas analyzer and a canister. The success and the measuring of the data in this experimentation were determined using the STATGRAPHICS Centurion XVI software. The results showed significant differences in fuel consumption and pollutant emissions of CO and NOx when applying an efficient driving, except for the HC in which there is no significant difference, but the emission is lower when is used on standard driving.
Abstract
This article presents the results of the impact of ecodriving on fuel consumption and the emission factors of polluting gases from a gasoline vehicle when performing road [...]
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Analysis of the safety compartment material of a light vehicle by multi-criteria method
E. Chamba, E. Llanes, A. Cardenas, W. Vega, J. Rocha

Enfoque UTE - Scientific Engineering Journal (2020). Vol. 11, (1), 2

Abstract
There is a wide variety of materials with various properties available for designers to meet different design requirements. The objective of this study was to evaluate the properties of the relevant materials available in Ecuador through the multicriteria meth-od such as: Proportional complex evaluation (COP-RAS), Technique for the order of preference for similarity to real solution (TOPSIS), Optimization multi-disciplinary and compromise solution (VIKOR), in order to indicate which material would be a potential substitute for the original. It was concluded that 1045 steel is the best choice as a substitute for a safety compartment compared the base line the Aluminum-Magnesium alloy, considering that, despite being a light material, has low resistance to impact forces.
Abstract
There is a wide variety of materials with various properties available for designers to meet different design requirements. The objective of this study was to evaluate the [...]
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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 [...]
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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 [...]
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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) [...]
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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 [...]
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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 [...]
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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 [...]
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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 [...]
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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 [...]
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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. [...]
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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 [...]
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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 [...]
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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 [...]
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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 [...]
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A paste slurry mass prediction numerical model for backfilling coal mining
W. Lv, X. Du, K. Guo

Rev. int. métodos numér. cálc. diseño ing. (2020). Vol. 36, (2), 31

Abstract
With the increasing importance of environmental protection, more and more attention has been paid to backfilling coal mining. The prediction and design of the proportioning of backfill materials are significantly important for paste backfilling coal mining. In this study, the key factors affecting paste slurry mass optimization are identified, including mass concentration, solid-cement ratio, and fly ash-cement ratio. According to the identified factors, a paste slurry mass prediction numerical model is established to effectively predict the paste slurry mass of backfilling mining, based on a hybrid algorithm of the back propagation neural network (BPNN) with chaos optimization (CO). With the adopted model indicators, the orthogonal test data of backfill materials are used as samples for learning, training and testing. The performance of the COBPNN and traditional BPNN models are assessed using experimental results. Finally, a mechanical model of gob-side entry retaining is development, and the surface convergence of surrounding rock of roadway and the internal load of filling body are detected in the tested working face. The results indicate that the proposed model has improved the performance of the traditional BPNN model, in terms of tardy convergence, low convergence precision, proneness to local minimum, enables high fitting accuracy and strong generalization, and more accurate and reliable prediction for the paste slurry mass, thus providing a more effective approach for optimizing the proportioning of paste slurry for backfilling coal mining.
Abstract
With the increasing importance of environmental protection, more and more attention has been paid to backfilling coal mining. The prediction and design of the proportioning [...]
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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 [...]
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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 [...]
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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 [...]
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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 [...]
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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 [...]
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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 [...]
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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 [...]
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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. [...]
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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 [...]
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La predicción del hinchamiento de suelos expansivos
E. Alonso, A. Lloret, A. Gens, F. Batlle

Boletin de la Sociedad Española de Mecánica de Suelos y Cimentaciones (1989). Vol. 1 (95), pp. 3-10

Abstract
El examen de ensayos de hinchamiento en laboratorio sugiere la existencia de dos etapas en las curvas expansión-tiempo. El primer mecanismo, de tipo «primario», se asocia con fenómenos de flujo no estacionario en la red de poros interconectados del suelo. Se piensa que el segundo mecanismo responsable del comporta miento a largo plazo, es el resultado de la hidratación de minerales arcillosos activos. Se ha desarrollado un modelo que incorpora estos dos mecanismos básicos. Las nociones actuales de microestructura de suelos han proporcionado un marco de referencia conveniente para la formulación teórica. El modelo se ha utilizado para reproducir ensayos edométricos de hinchamiento de margas expansivas. Los parámetros derivados en el proceso de ajuste ensayo modelo se han utilizado para reproducir los hinchamientos medidos, a lo largo de diez años, en una central nuclear cimentada sobre margas expansivas
Abstract
El examen de ensayos de hinchamiento en laboratorio sugiere la existencia de dos etapas en las curvas expansión-tiempo. El primer mecanismo, de tipo «primario», [...]
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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 [...]
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Anisotropy in 2D Discrete Exterior Calculus
. , H. Esqueda, R. Herrera, S. Botello, C. Valero

Collection title not available (2020). 1

Abstract
We present a local formulation for 2D Discrete Exterior Calculus (DEC) similar to that of the Finite Element Method (FEM), which allows a natural treatment of material heterogeneity (assigning material properties element by element). It also allows us to deduce, in a principled manner, anisotropic fluxes and the DEC discretization of the pullback of 1-forms by the anisotropy tensor, i.e. we deduce the the discrete action of the anisotropy tensor on primal 1-forms. Due to the local formulation, the computational cost of DEC is similar to that of the Finite Element Method with Linear interpolating functions (FEML). The numerical DEC solutions to the anisotropic Poisson equation show numerical convergence, are very close to those of FEML on fine meshes and are slightly better than those of FEML on coarse meshes.
Abstract
We present a local formulation for 2D Discrete Exterior Calculus (DEC) similar to that of the Finite Element Method (FEM), which allows a natural treatment of material heterogeneity [...]
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CFD analysis of flow pattern in labyrinth weirs
F. Salazar, J. San Mauro, M. Toledo

(2015). Dam Protections against Overtopping and Accidental Leakage, Ed: CRC Press, 287 p.

Abstract
The hydraulic performance of a labyrinth weir was analysed using numerical simulation. The head-discharge relation was compared to the results of an empirical formula, and the flow 3D pattern was studied. The results showed the reliability of the numerical model results, especially for intermediate to high heads. Moreover, they were used to unveil complex phenomena that are difficult to observe in laboratory tests.
Abstract
The hydraulic performance of a labyrinth weir was analysed using numerical simulation. The head-discharge relation was compared to the results of an empirical formula, and [...]
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Highly-converging chutes as an overtopping protection for concrete dams: physical and numerical modelling
L. Morera, J. San Mauro, F. Salazar, M. Toledo

(2015). Dam Protections against Overtopping and Accidental Leakage, Ed: CRC Press, 245 p.

Abstract
Spillways with highly-converging chutes are a non-conventional kind of spillway in which the length of the crest is greater than the width of the stilling basin. A pair of converging chutes leads the water into the stilling basin. This typology has two possible advantages: increase of the discharge capacity or reduction of the hydraulic head for a given discharge flow. The first improves dam safety, whereas the second results in higher storage capacity and power generation. In this proceeding, the authors present the investigation performed in order to study and characterize this kind of spillways. The utilization of this typology as an overtopping protection has emerged as a third possibility, presenting some particularities that are introduced here.
Abstract
Spillways with highly-converging chutes are a non-conventional kind of spillway in which the length of the crest is greater than the width of the stilling basin. A pair of [...]
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Physical and numerical modeling for understanding the hydraulic behaviour of Wedge-Shaped-Blocks spillways
F. Caballero, F. Salazar, J. San Mauro, M. Toledo

(2015). Dam Protections against Overtopping and Accidental Leakage, Ed: CRC Press, 193 p.

Abstract
The technology of Wedge Shaped Blocks (WSB) for spillways had a slow development through decades but has proven its practical reliability. Ongoing additional research aims to complete the theoretical knowledge, improve current design criteria and make this technology available to practitioners as one more solution to consider when designing an embankment dam spillway. Here a summary is provided about recent physical and numerical modelling of WSB spillways performed by UPM and CIMNE.
Abstract
The technology of Wedge Shaped Blocks (WSB) for spillways had a slow development through decades but has proven its practical reliability. Ongoing additional research [...]
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