Scipedia: Documents published in 2024

PLENARY LECTURE - Instrumental Dynamic Penetrometers for Geotechnical Characterization

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 12:05:30 +0200

The dynamic penetrometer is a common technique in geotechnical exploration and widely deployed throughout the world. However, while this technique has many advantages, it also has several disadvantages that can hinder its use and development. Indeed, it has evolved little, and its application has sometimes remained "rustic". But in recent years with the development of sensors, interpretation methods and digital technology, this technique has been adapted to improve the quality of measurement, the understanding of the phenomena occurring during the test and its exploitation. This article presents the recent developments and adaptations of this technique and their potential. After a brief review of the principle, history, and current limitations of the technique, we look at recent technological developments and the latest advances in terms of interpreting and using the test.

PLENARY LECTURE - Simulation-aided geotechnical site investigation

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 12:05:12 +0200

With the advancement of computational geomechanics over the past decades, most of the activities typical of site characterization, such as in situ testing or sampling, can be realistically simulated using appropriate constitutive models and balance equations for geomaterials. These numerical simulations are not only informative of the processes that take place during testing but can be used to assess the reliability of current practice empirical interpretation techniques or even propose new interpretation techniques. In this paper, we present two numerical analyses of long-standing geotechnical problems in which new insights are gained by means of advanced numerical modelling. The first analysis corresponds to cone penetration testing in undrained, brittle geomaterials; we describe the effect of the constitutive parameters on cone metrics, and we propose a novel procedure to estimate the initial state parameter from CPTu based on a wide-ranging parametric analysis. The second analysis involves tube sampling in undrained geomaterials. A total stress analysis allows us to describe the kinematics of the soil during tube insertion and evaluate the effect of the tube geometry on the strain path of the problem. The analysis is then extended by considering a fully coupled hydromechanical formulation and a critical state constitutive model for cemented soils; by simulating conventional laboratory tests on the soil that has entered the tube we can quantify sampling disturbance in terms of geotechnical design parameters (e.g. undrained shear strength and yield stress). The possibilities offered by numerical modelling for site characterization are far from being fully exploited. It is envisaged that in the future site-specific numerical analyses will become available, enabling a more comprehensive understanding of the subsurface conditions.

PLENARY LECTURE - Treatment of uncertainties in site characterization in second-generation eurocode 7

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 12:04:57 +0200

The purpose of this paper is to introduce the geotechnical engineering community to the treatment of uncertainties in site characterization within the framework of the second-generation Eurocodes. To do so, the main uncertainties related to the Ground Model, the ground properties and the groundwater levels are described before discussion of the statistical and modelling involved. This paper also explains the determination of “representative values” of ground properties within the framework of the Second-Generation Eurocode 7, either selecting the value based on engineering judgment and comparable experience, being in this case termed a “nominal value”; or evaluating the value by statistical methods, being in this case termed a “characteristic value”. Additionally, since 2nd-Gen Eurocode 7 allows using reliability-based methods for the verification of limit states, the paper gives some guidance for choosing probability distribution types, and for assessment their parameters like the mean and standard deviation. Finally, two examples are provided to show how to deal with the new elements involved with uncertainty treatment in terms of statistical analysis and probabilistic modelling

PLENARY LECTURE - Recent advancements in data-driven site characterization

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 12:04:24 +0200

This paper reviews some recent advancements that address the challenges faced by the broad application area of datadriven site characterization (DDSC). The challenges include the ugly-data challenge, site-recognition challenge, and stratification challenge. The ugly-data challenge is about the MUSIC-3X attributes of the site investigation data, where MUSIC-3X stands for multivariate, uncertain and unique, sparse, incomplete, possibly corrupted, and 3D spatial variability (3X). The site-recognition challenge is about the site-uniqueness feature of the site investigation data. The stratification challenge is about the task of layer delineation in soil profiling. In recent years, some studies have been conducted to address these challenges with an encouraging degree of success, which are briefly reviewed in this paper. However, there are still unresolved issues yet to be addressed, which are briefly summarized in this paper as well.

PLENARY LECTURE - Combined resistivity and seismic measurements along linearly extended earth structures - acquisition and interpretation approaches

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 12:04:10 +0200

Geotechnical parameters of linearly extended earth structures, such as embankments and earth dams, are usually obtained from localized investigations through drilling or penetration tests, commonly time and cost consuming. Non-invasive geophysical investigations may be considered an alternative approach for the geotechnical characterization of these structures, given their surveying speed and their depth and length of investigation. Particularly, new acquisition approaches with the use of appropriate streamer cables could strongly reduce the acquisition times making geophysical surveys ideal for a preliminary screening of these structures. Specifically, resistivity and seismic methods can be adopted given that these two methodologies could offer complementary information with respect to the pore fluid properties (resistivity methods) and the solid skeleton characteristics (seismic methods). Also, through specific correlations, relevant geotechnical parameters for the evaluation of the stability of these structure and its efficiency (i.e. hydraulic conductivity, porosity and others) can be obtained. In this paper a review of the methodologies developed in recent years for data acquisition along linearly extended earth structures is reported with special focus on the use of combined electric and seismic streamer cables. Suggestions with respect to interpretation approaches and data elaboration are also analysed.

PLENARY LECTURE - Passive seismic methods for site characterization

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 12:03:57 +0200

Site characterization methods to extract the shear-wave velocity (Vs) structure over the first few tens to few hundred of meters or the soil’s resonance frequency using seismic noise recordings have become widespread over the last 40 years. Being cost-effective and easy to implement, especially in urban environment, passive seismic methods have been shown reliable to retrieve the soil resonance frequency and the Vs profile of near-surface geological layers. International efforts over the last 20 years have outlined the capabilities and limitations of passive seismic methods and lead to a series of good-of-practice, state-of-the-art and recommendations on data acquisition and processing. Recent methodological developments using three-component single-station and three-component array methods are promising approaches to better constrain Vs profiles. Also, the very high spatial and temporal resolution offered by the Distributed Acoustic Sensing (DAS) makes this emerging technology one with very high potential for near-surface site characterization, especially in urban environment.

PLENARY LECTURE - Machine learning tools for the treatment of offshore site investigations

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 12:03:44 +0200

During geotechnical and geophysical site characterisation for large infrastructure projects, significant data volumes are being collected which need to be processed and interpreted. Due to the limited budgets available for site characterisation and the various sources of uncertainty, the interpretation relies on a combination of data from various sources (e.g. in-situ and laboratory tests), the use of parameter correlations from the literature and expert judgement. In recent years, modern data science techniques have become increasingly accessible to practicing engineers and researchers and they offer the possibility to improve several aspects of the site characterisation and parameter selection process. Machine learning models can be trained on high-quality datasets and expert judgement can also be internalised in the model formulations. In this contribution, the role of data science and machine learning for geotechnical site characterisation is discussed based on several example applications using datasets from offshore wind farm projects. The role of data coverage and data quality is discussed as well as the role of geophysical data for interpolating geotechnical point measurements in a quantitative way. Supervised and unsupervised machine learning techniques are explained and illustrated on the provided datasets. Finally, a perspective is given on the role of the emerging Large Language Models (LLM) for geotechnical site characterisation applications.

PLENARY LECTURE - Bio-inspired site characterization - towards soundings with lightweight equipment

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 12:03:28 +0200

Equipment used for site investigation activities like drill rigs are typically large and heavy to provide sufficient reaction mass to overcome the soil’s penetration resistance. The need for large and heavy equipment creates challenges for performing site investigations at sites with limited accessibility, such as urban centres, vegetated areas, locations with height restrictions and surficial soft soils, and steep slopes. Also, mobilization of large equipment to the project site is responsible for a significant portion of the carbon footprint of site investigations. Successful development of selfburrowing technology can have enormous implications for geotechnical site investigation, ranging from performance of in-situ tests to installation of instrumentation without the need of heavy equipment. During the last decade there has been an acceleration of research in the field of bio-inspired geotechnics, whose premise is that certain animals and plants have developed efficient strategies to interact with geomaterials in ways that are analogous to those in geotechnical engineering. This paper provides a synthesis of advances in bio-inspired site investigation related to the (i) reduction of penetration resistance by means of modifying the tip shape, expanding a shaft section near the probe tip, applying motions to the tip like rotation and oscillation, and injecting fluids and (ii) generation of reaction forces with temporary anchors that enable self-burrowing. Examples of prototypes that have been tested experimentally are highlighted. However, there are important research gaps associated with testing in a broader range of conditions, interpretation of results, and development of hardware that need to be addressed to develop field-ready equipment that can provide useful data for geotechnical design.

Impact of evolving fabric anisotropy on CPT simulations for subsurface characterization

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 11:27:24 +0200

In geotechnical site characterization, Cone Penetration Testing (CPT) is a fundamental method for evaluating subsurface conditions of granular materials such as sands, silts, and non-plastic tailings. This study advances CPT simulations by incorporating the fabric anisotropy variable A into the SANISAND-F model and utilizing the Material Point Method (MPM), with a specific focus on the role of evolving fabric within an anisotropic critical state framework. The objective is to deepen the understanding of how the evolving fabric of soils influences macroscopic site characterization outcomes. Through carefully controlled initial conditions, including void ratio and confining pressure, the study aims to demonstrate the impact of fabric anisotropy on CPT resistance measurements. Assessment of the evolution of material state based on the key constitutive ingredient of the model allows for explaining the reason behind the respective values of cone tip resistance observed from the CPT simulations, considering fabric anisotropy and the anisotropic critical state framework. This approach enhances the modeling of this site characterization method, providing a more comprehensive framework for interpreting soil mechanical behavior and enhancing predictive modeling capabilities

Use of the Pocket G-PFEM to Predict Changes in Soil State

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 11:26:25 +0200

Simulating the CPTu response to changes in the current soil state allows geotechnical engineers to evaluate different scenarios and better predict the structure’s performance. Developed by the Universitat Politècnica de Catalunya, Centre Internacional de Mètodes Numèrics en Enginyeria and TU Graz, the Pocket G-PFEM is a numerical tool that simulates the CPTu in a homogeneous soil layer, adopting an updated Lagrangian description. Two types of cones can be simulated: i) the smooth cone, without lateral friction in the interface cone/soil, and ii) the rough cone, with lateral friction. The Clay and Sand Model is adopted as the soil constitutive model. This study assessed the software response to changes in the overconsolidation ratio (OCR) and compressibility parameters (λ and κ) in both cone modules. The rough cone analyses resulted in higher qt and u1 than the smooth cone, but no significant change was observed in u2 and u3. The Pocket GPFEM could partially reproduce the expected behaviours from the literature, but u2 and u3 did not decrease significantly for high OCRs, and the rough cone could not adequately simulate the fs. Following the literature, qt was mainly sensitive to λ for the OCR = 1 and to κ for the OCR = 2, but an unexpected behaviour was observed for the OCR = 8 when changing λ and κ. The results show Pocket G-PFEM’s limitation in reproducing qt, fs, and u for high OCRs. It might be related to the adopted parameters, and different sets should be evaluated.

Types of Shearing and Anisotropy in Undrained CPTu

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 11:25:25 +0200

Most natural clays acquire an anisotropic fabric upon deposition. This anisotropic fabric induces differences in the soil mechanical responses, for instance in the undrained shear strength observed in the laboratory. It is unclear how much of that anisotropy is reflected on the responses measured by the cone penetration test. In this work, we use GPFEM to numerically simulate cone penetration tests (CPTu) in undrained, anisotropic clays. The constitutive response is represented by S-CLAY1, a critical state, anisotropic model. Full details of the representative stress path during CPTu insertion are provided. Preliminary numerical results suggest that even a large amount of anisotropy, as described by the model, will have a very small effect on the cone responses. The numerical simulation results also show that the prevailing stress path has strong similitudes with that found during anisotropically-consolidated undrained compression triaxial test.

Analysis of Video Images obtained during Cone Penetration Testing

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 11:24:25 +0200

One of the ways to enhance the efficiency of the cone penetration testing process is to mount modules behind the cone. In this way the test will not only generate the standard Cone Penetration Testing (CPT) data (i.e., cone tip resistance, sleeve friction, and dynamic pore water pressure), but also the data obtained by the module pushed into the soil together with the cone. While for certain modules it is common practice to analyze the acquired data extensively (e.g., the seismic module) for other modules this is not necessarily the case. A good example of the latter is the video module, which has been available for several decades. When this module is deployed with visible light, the analysis is typically limited to viewing the recording and adding observation notes. During the recent TRIM4 research project the video module was deployed and subsequently attempts were made to identify the soil type through an automatic analysis of the video images and to characterize and to determine the grain size distribution using the video images. This approach is highly correlated with the soil behavior type index, commonly used in the analysis of CPT data, and at the same time mitigates the effect of the CPT data reflecting changes in soil strength behavior before a layer is actually penetrated by the cone. In this paper the authors will describe the use of the video cone in very general terms, but focus on this analysis methodology in detail

Interpretation of cone pressuremeter tests to estimate the strain dependent stiffness and strength of sensitive lacustrine clay

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 11:23:25 +0200

Field and laboratory testing was carried out for the construction of a 100 m long cable stayed bridge situated in the foothills of the Alps in the south of Germany, a region dominated by deep post-glacial, fine-grained sediments. Due to the sensitivity and associated challenges with retrieving undisturbed soil samples in situ tests and their evaluation proved to be essential for the geotechnical design of the bridge foundation. This contribution focuses on the analytical and numerical interpretation of Cone Pressuremeter Tests (CPM). The non-linear ðº-ð¾ relationship and undrained shear strength (using both the limit pressure and reverse plasticity contraction analysis) were determined analytically. Numerical investigations were carried out as verification using both the Finite Element method (FEM) using both 1D (cavity expansion) and 2D simulations (where the penetration of the probe was modelled) as well as using the Finite Difference (FD) method. 2D simulations demonstrated that the assumption of the cylindrical cavity expansion is appropriate for modelling the CPM tests. The interpreted undrained shear strength showed good agreement with other field tests, including CPTu, vane shear (FVT) and seismic cone penetration (SCPT) tests, as well as with the results of laboratory tests on disturbed samples. CPM tests with strain rate jumps were conducted during pressuremeter expansion, wherewith it was possible to quantify the viscous response of the soil. Based on the holistic interpretation of the field and laboratory results involving both numerical simulations and analytical methods the parameters for the material model Viscohypoplasticity were calibrated.

Plant Root Circumnutation-Inspired Penetration in Sand and Clay

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 11:22:24 +0200

Site investigation (SI) and subsurface exploration are vital for characterizing soil properties. However, a common challenge is the lack of sufficient reaction force to penetrate through stiff crusts or deep layers, leading to refusal. To address this issue, rigs typically have large sizes that can make mobility and accessibility challenging and increase the carbon footprint of SI activities. This paper experimentally investigates a plant root-inspired strategy called circumnutation-inspired motion (CIM) to reduce the vertical penetration forces (ð¹ð§) in comparison to quasi-static penetration used for example for Cone Penetration Testing (CPT). The CIM probes have a bent tip end and are rotated at a constant angular velocity (ð) while they are advanced at a constant vertical velocity (ð£) in uniform specimens of clay and sand. ð¹ð§ for both soils decay exponentially by factors as high as 10 with increasing relative velocity, defined as the ratio of the tangential to the vertical velocity of the probe tip (ðð/ð£). Torques for both soils increase with initial increases in ðð/ð£ which stabilize at higher velocities. While the cumulative total work, calculated for both clay and sand from the measured forces and torques, increases less than 25% for initial increases in ðð/ð£ between 0 and 0.3ð, the ð¹ð§ can be reduced by around 50%. Thus, CIM penetration can produce significant reductions in ð¹ð§ in comparison to CPTs while limiting the additional energy consumed. CIM could be implemented to perform site investigation activities, such as obtaining samples or installing sensors, using smaller-sized, light-weight rigs

G-PFEM-aided Derivation of Undrained Shear Strength of Organic Clays from CPT Data

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 11:21:25 +0200

Accurate evaluation of undrained shear strength of soils is crucial in geotechnical design and assessment. In the practice, undrained shear strength is obtained most frequently from CPT data, dividing the net cone tip resistance by a cone factor, ð . For organic soils, values between 8.6 and 15.3 are reported, depending on the stress history. The cone factor can be conditioned to the results of laboratory tests, although uncertainties remain on the variety of stress paths followed by the soil elements around the tip of the cone, compared to the ones tested in the laboratory. Non-uniqueness in the definition of the cone factor may lead to either unsafe or over-conservative choices, partly undermining both the reliability and the sustainability of the design. This contribution analyses numerically the inversion technique used to determine the undrained shear strength of organic clays, exploiting data from an extensive in situ and laboratory investigation. The adopted constitutive model was calibrated on the results of laboratory tests. Cone penetration tests were simulated performing coupled hydro-mechanical numerical analyses via G-PFEM, developed in the last decade at CIMNE-UPC. The role played by initial stress state and previous stress history upon stress distribution at failure, cone factor and sleeve friction is discussed. The numerical results suggest how the sleeve friction could be used to condition the cone factor depending on the over-consolidation ratio and demonstrate how combining the different available CPT readings with the aid of numerical results may reduce the uncertainty in the estimation of undrained shear strength.

A numerical analysis of CPT-based tip resistance prediction during pile installation in clays

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 11:20:24 +0200

Accurately predicting the installation resistance of offshore piles is important for their design and application. The cone penetration test (CPT) is the most widely used in situ sounding tests for pile drivability analysis and capacity prediction. While there are established empirical correlation methods to connect CPT data with pile installation resistance, the underlying mechanisms behind these correlations have yet to be fully understood. This study performs a numerical analysis to reveal such mechanisms and improve the correlations. The pile installation and cone penetration processes are modelled using a large-deformation finite-element method. For all analyses, a smooth cone and a smooth pile are simulated to quantify the relationship of tip resistance between the pile and CPT. The mechanisms of the two analogous penetration processes are visualized and compared through numerical modelling. As the cone advances, it pushes the soil at the cone tip into the far field. During the pile penetration process, soil heaving can be observed with the soil surface inside the pile moving above the mudline. The soil failure is localized at a small zone around the pile tip. The penetration resistances of pile are correlated to CPT data with the aid of numerical modelling and compared to existing CPT-based design guidelines. A discussion on the pile tip resistance correlated with cone tip resistance is included, and the value of the empirical coefficient for tip resistance kp is obtained.

Prediction of state parameter based on CPT MPM simulations in sandy soils

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 11:19:24 +0200

Cone penetration tests (CPTs) can provide quantitative information about the mechanical state of sandy soils. In the current state of the art, the soil state is derived from the cone resistance, which is estimated from the cavity expansion solution and a calibrated scaling equation. Recently, Martinelli and Pisano (2022) showed that MPM simulations of CPTs provide accurate values of the cone resistance in sandy soils when using the critical state NorSand model. This paper adopts this framework to develop a predictive equation for cone resistance as a function of the NorSand parameters and the state parameter of the soil. This formula is straightforward to implement, and it can be adopted by researchers and practitioners to assess soil state in a soil deposits.

Numerical Study of Cone Penetration in Calcareous Sands: Investigating Cone Tip Resistance Correction Factors for Crushable Soils

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 11:18:51 +0200

The cone penetration test (CPT) is used to characterize the behaviour and properties of soils, including the cyclic strength against earthquake liquefaction triggering. The cone tip resistance relates to cyclic strength through relative density, where relative density is closely related to both cone tip resistance and liquefaction susceptibility. Currently, published methods of estimating liquefaction potential (i.e., cyclic resistance ratio) are based on silica sands and do not properly characterize calcareous sands. The measured cone tip resistance in calcareous sands is lower than in silica sands at the same relative density; this difference is generally attributed to the higher compressibility of calcareous sands due to particle crushing during cone penetration. Consequently, application of CPT-based liquefaction triggering evaluations in calcareous sands result in over-conservative analysis. To avoid over-conservative analysis, projects may develop site-specific correction factors to adjust the cone tip resistance in calcareous sand to the equivalent value in silica sand at the equivalent relative density. This study aims to investigate cone penetration in calcareous sands compared to silica sands by examining the roles of soil compressibility and other fundamental soil parameters. The study is performed with a direct axisymmetric penetration model and the MIT-S1 constitutive model calibrated against published mechanical behaviour for a calcareous sand; the simulated cone penetration results are compared with simulated cone penetration in Ottawa F-65 sand. Compressibility of the calibrations is adjusted to explore the role of compressibility on cone tip resistance. The numerical results show that differences in compressibility only partially account for differences in cone tip resistance between calcareous and silica sands at the same initial state. However, the results support that critical state line position does strongly relate to differences in cone tip resistance between the two soil types. The study results provide a basis to investigate differences in critical state line position as a basis for site-specific cone tip resistance correction factors for calcareous soils.

On the Determination of Soil Deformation Modulus by Means of a Penetrometer

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 11:18:31 +0200

Classical Cone Penetration Test (CPT) or CPTu (when water pore pressure is also measured) can provide so far only strength parameters of soils, specifically the tip resistance and the lateral friction. This article presents the numerical simulation in a (virtual) calibration chamber, using the Discrete Element Method (DEM), of a CPT-based test proposed in the quest for possibilities to determine soil deformability parameters as well. It is a non-standard test characterized by force-controlled cycles applied to the penetrometer tip that is movable independently of the penetrometer body. Very small irreversible displacements of the tip are observed over the first cycles whose amplitudes span a region of low fractions of the tip resistance, that is subsequently assimilated to a pseudo-elastic domain within which, deformation moduli can be derived from the slopes of the force-displacement curve properly interpreted. Results also reveal a loading level beyond which, these slopes and the corresponding deformation moduli, significantly decrease while the irreversible displacements of the tip increase substantially.

Experimental and Numerical Investigations of CPT End Resistance at Variable Penetration Rates in Mixed Soils

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 11:18:05 +0200

This paper investigated cone penetration test end resistance under various drainage conditions in mixed soils through numerical simulations and piezocone experiments in laboratory testing chambers. The soil samples used in the laboratory tests contained various proportions of kaolin, silt, and sand. The piezocone tests were performed using a 10 mm diameter cone in consolidated soil samples. The measured variations of cone resistance and pore pressure at cone velocities varying from 0.005 mm/s to 30 mm/s are presented, which covered the full range from drained to undrained conditions. The cone resistance was evaluated using the spherical cavity expansion limit pressure predicted in Finite Element (FE) analyses that employed the NorSand (NS) constitutive model. The experimental and numerical findings allow assessment of the suitability of the normalised velocity (V) term, proposed by others, to unify cone resistances measured at variable rates.

Numerical Simulations of Cone Penetration Response via Accounting for State-Dependence and Full-Strain-Range Non-Linearity of Sand

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 11:17:40 +0200

The penetration response of CPT is not only related to the stress and density states of sand but also influenced by the nonlinear stress-strain relations of soils from very small (10-5) to relatively large (10-1) strain levels. Appropriate considerations of the above key soil behaviours can be crucial for accurate numerical simulations of CPT response. For this purpose, an intergranular strain (IGS)-based elastic model is introduced into a critical-state-based, state-dependent plasticity model to capture the state-dependence and full-strain-range non-linearity behaviour of sand. A numerical model of the CPT penetration process is then established by combining the aforementioned constitutive model and the arbitrary Lagrangian-Eulerian (ALE) large deformation finite element technique. The latter is adopted to handle the problems of large deformations of soil and mesh distortion. Then the computed response of CPT is compared against centrifuge test observations, and the numerical model is utilized to analyse the influences of the full-strain-range non-linearity behaviour of sand on the penetration response of CPT. The results indicate that the non-linear stress-strain relations at small strains can have noticeable impacts on the tip resistance of CPT, in particular for loose sand, while having a relatively small influence on the penetration depth required to reach a steady-state penetration resistance. The above influences might be attributed to a rapid decay of soil strains with the distance from the cone tip, and consequently high stiffness and strong constraints effects of far-field soils on core soils adjacent to the cone tip

Inherent and CPTu-measured Scale of Fluctuation of Undrained Geomaterials: a Numerical Perspective

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 11:17:23 +0200

The vertical scale of fluctuation of soil parameters is often indirectly estimated through Cone Penetration Testing (CPTu) as the test provides nearly continuous and repeatable data. However, the variability quantified from CPTu might not be representative of a soil parameter intra-site variability, but rather the effect of the variability of soil measured through its response to the cone probe. The objective of this work -of an openly prospective nature- is to examine how the vertical inherent spatial variability of clay-like insensitive geomaterials propagates to the cone tip and friction sleeve resistance by means of numerical modelling. A total stress analysis is presented, in which the undrained shear strength is described according to random field theory. Numerical results show that the scale of fluctuation of the tip resistance and friction sleeve resistance is greater than the one assumed for undrained shear strength.

A DEM Study on the Effect of Chamber Boundary on CPT Calibration Chamber Tests

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 11:17:09 +0200

Laboratory-scale cone penetration tests are often carried out to calibrate the response of cone penetration, and in particular cone tip resistance to soil characteristics. However, because of the limited sample size, sample boundaries can often affect the measured cone resistance in laboratory tests. This paper presents numerical simulations using the discrete element method (DEM) to study the effect of boundary condition on cone penetration calibration chamber tests. Numerical simulations were performed under flexible (BC1) and laterally-constrained (BC3) boundary conditions on K0consolidated models at different relative densities and vertical stresses. Additional models were simulated with periodic boundaries (BC5) to model the free-field condition. To track the radial stress variations in different sections of the chamber, scattered representative volume elements (RVE) were embedded in the models. Particle displacements and contact force chains were examined to determine the relation between microscopic variables and macroscopic response of the specimens subjected to cone penetration under different boundary conditions. Larger cone resistances were obtained under BC3 condition than those in BC1 condition. For the chamber-to-cone diameter ratio of 25 adopted in this study, the influence of the lateral boundary was found to be negligible in loose to medium-dense assemblies, while the effect of chamber boundary amplified in dense to very dense samples with increasing relative density and reduced with increasing vertical stress. This was attributed to the higher radial stress induced along the cone penetration path in laterally-constraint BC3 models. Based on these findings, a correction factor is proposed to better estimate free-field penetration resistance from calibration chamber experiments.

The evolution of Menard pressuremeter cavity preparation in France

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 11:09:24 +0200

Since Louis Ménard invented his first pressuremeter prototype in 1954, the pressuremeter and its placement techniques into the ground have gone through numerous advancements. In this paper, the authors review the cavity preparation developments in France from the early days of developing the pressuremeter to contemporary times. Pressuremeter probes were initially installed using hand augers, which was quite time consuming and cumbersome. Soon after, drilling was mechanized using drilling rigs with various abilities and capacities in the form of rotary and percussion drilling. Specific techniques such as STAF, RotoSTAF, and similar devices have now been developed to create holes with minimum disturbance in the ground.

Subsurface Characterization of Coastal Deposits using Measurement While Drilling

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 11:08:34 +0200

Measurement While Drilling (MWD) is a promising in situ test method that has gained increasing popularity in recent years. MWD can continuously characterize the subsurface while drilling any type of borehole in soil or rock without interfering with normal drilling operations. The latest MWD equipment gathers real-time data on numerous parameters that capture all aspects of the drilling process (e.g., depth, down thrust, rotation, torque, mud flow, and mud pressure). This paper summarizes MWD assessments performed in the coastal deposits of New Hampshire, USA. Profiles of individual and combined drilling parameters were used to differentiate between different soil layers and characterize subsurface conditions in complement with conventional, standardized geotechnical testing (e.g., SPT, CPTU) performed at adjacent boreholes. The results from this experimental campaign demonstrate the applicability of MWD systems to evaluate a broad range of geological conditions, from granular soils with erratic boulders to sensitive clays.

Using Drilling Data to Derive Geotechnical Properties of Variably Cemented Materials

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 11:07:25 +0200

Geotechnical site characterisation of variably cemented material is often challenging due to lack of data. Drilling data is routinely measured as a part of standard geotechnical site investigation and can provide an alternative method to derive continuous ground profiles with depth. This paper examines the use of drilling data for site characterisation purpose. Based on the drilling data obtained from an offshore windfarm project site, where variably cemented materials were found, it is shown that the borehole specific energy calculated using the drilling data reasonably captures the variation in material types with depth. Also, the results show that borehole specific energy can be correlated with the laboratory test data in a similar manner to cone penetration test. Based on the results obtained from different locations covering a range of material types and in-situ state conditions, generalised relationships between different geotechnical parameters and borehole specific energy are presented. An example of how the generalised relationships developed using borehole specific energy can be used to derive design profiles for a selected site is also shown. The data and interpretation approach presented in this paper provide a useful guide for how the drilling data can be used to assess the continuous ground profile for variably cemented sites where only limited or no in-situ test and intermittent sampling data are available.

Offshore rock investigations by a remotely operated submersible drilling rig with continuous drilling recording

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 11:06:36 +0200

The submersible drilling rig presented in this paper was designed and constructed with the aim to allow conducting soil or rock characterization in offshore investigations in shallow water projects when short target penetrations are required. The system is instrumented with sensing elements allowing the full control of the operation in real-time for three different purposes: (i) positioning, (ii) continuous drilling parameters (MWD, measuring while drilling) and (iii) visual inspection. The suitability in sandy and silty soils was reported by Romero et al. (2012). The system is outstanding as an interesting alternative to traditional methodologies for rock investigations in relative shallow water projects where the knowledge of the first metres of rock profile is critical (e.g., pipelines, submarine interconnections, dredging, foundations). Some benefits of the system are presented in this paper, especially in ground models composed of a rock layer underneath a soil deposit or by rocks with variable strength with depth.

Comparison of Direct and Indirect MWD Measurements

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 11:06:14 +0200

Drilling boreholes for geotechnical purposes such as sampling and in situ tests is usually performed with the aid of drilling machines. In France, typically, the machine’s drilling parameters such as applied torque and thrust are monitored in realtime and registered so that information about the subsoil’s structure can be acquired. As these machines tend to use hydraulic systems, the oil pressures fed into each motor and actuator are the parameters commonly monitored. Recently, a new type of sensor and its application in geotechnical investigations through the measuring of drilling parameters was presented. This sensor is directly mounted on top of the drill string of a drilling machine and records the actual thrust, torque, and rotation speed transmitted to the drill string and bit. This bypasses the energy losses present in the hydraulic circuit between the machine’s pressure sensors and the hydraulic actuators. This mounting position allows a more accurate measurement of the forces and, furthermore, the effective rotation speed applied to the drill bit. The data is transmitted through a wireless Bluetooth connection enabling real time monitoring. Nevertheless, finding the right balance between a soil’s resistance, the drill rig’s power and the sensor’s optimal measuring range remains a topic for further development. This analysis of several worksites with different soils throughout France contributes to a better understanding of the last generation’s sensor’s precision and application range.

Comparative Analysis of Different Methods for Interpreting MWD Profiles

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 11:05:52 +0200

To determine a robust geotechnical model from measurements of drilling parameters is one of the great desires of geotechnical investigations. Drilling parameters have the advantage of presenting very granular data (data-points every centimetre) much like the CPT. They allow for the identification of soil samples during the drilling process and can traverse all terrain types, from soft clays to hard rocks. However, interpreting each parameter, like penetration rate or thrust, in isolation can be challenging, as these parameters can vary greatly within each soil layer due to natural heterogeneity, the drill rig’s configuration and the noise introduced by the discontinuous interaction between soil and drill bit. Various authors propose using compound parameters such as specific energy, penetration resistance and alteration index alongside cautious filtering allows for a better interpretation, giving physical meaning to the measurements. These compound parameters have been developed from simple correlations, aiming to normalise parameters heavily influenced by drilling conditions or even aiming to evaluate the work or the energy spent in excavating the soil. Beyond that, many authors have devised algorithms to automate or standardize the interpretation of drilling logs by identifying homogenous zones or the probability that a given point belongs to a certain layer. This paper presents a comparison of such methodologies for identifying soil layers based on MWD profiles proposed in the literature. Assessment of the geotechnical structure may be made through different analytic and advanced statistical methods. MWD profiles from worksites throughout France will be used to compare and qualify these methods.

Organization and Analysis of Measurement While Drilling (MWD) Data in Montana, USA

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 11:05:34 +0200

Use of a portable measurement while drilling system for shallow subsurface characterization

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 11:05:13 +0200

The Portable Measurement While Drilling (PMWD) equipment designed by CEREMA engineers is an innovative and lightweight tool to perform rapid assessment of shallow subsurface conditions. The equipment consists of sensors mounted on a cordless rotary drill that records depth, downforce, rotation, torque, and time. This paper presents results obtained with the portable MWD under laboratory and field conditions, which were directly compared to soil resistance profiles obtained with a lightweight dynamic cone penetrometer (LDCP – PANDA). Results from 66 PMWD profiles and 87 LDCP profiles demonstrated the potential applicability of the portable MWD in shallow subsurface investigations. A linear correlation between the Somerton Index (SD) and the LDCP tip resistance (qd) was obtained in granular soils under controlled conditions, ranging from sand (SP) to sandy gravel (GP). The obtained relationship was applied to MWD results from a 180-m long, 50-m tall grassy slope in New Hampshire, USA. It was observed that the estimated qd values from drilling parameters have a good correspondence with LDCP results at the same testing locations. Shallow subsurface characterization using MWD can potentially be used for shallow foundations, compaction control, pavement subgrade evaluation, and areas prone to geotechnical hazards not easily accessible through usual exploration methods.

Prediction of Land Surface Subsidence in the U2 Metro Tunnel in Vienna

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 10:56:20 +0200

This paper discusses the numerical and probabilistic modelling of the tunnel construction concerning some not yet completed sections of the Vienna U2 metro line. It presents the algorithm and results analysis of numerical simulation for the step-by-step tunnel construction using the New Austrian Tunnel Method (NATM) in a dense urban environment. The nature and magnitude of subsidence of the earth surface depending on a number of factors involved in the calculation scheme are determined, and all parameters of the stress-strain state of the system "tunnel - ground mass" are obtained. A methodology is proposed for determining reliability by the criterion of additional vertical subsidence of the ground surface which accompanies underground construction. By comparing the results of numerical modelling, empirical calculation and geotechnical monitoring of the metro construction site, it is shown that they correlate well enough with each other. The results of this study can be used to predict the level of the ground settlement during tunnelling works in areas of dense urban development

The importance of laboratory proficiency testing schemes in assessing and improving uncertainty

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 10:56:02 +0200

Any site characterisation relies on at least some laboratory tests, and some of those test results (often from basic tests such as Liquid Limit and Plastic Limit) are used in initial design calculations based on correlations. However, the reliability of those correlations is heavily dependent on the uncertainty in the results of those laboratory tests. There is an inter-laboratory proficiency testing scheme that has been running for over fifteen years in the UK, with many worldwide participants. This paper presents a compilation of the scheme’s findings to allow an assessment to be made regarding the reliability of different tests. As an example, repeatability within a single laboratory for the Liquid Limit test by cone penetrometer has been shown to be ± 1 %, but between different laboratories this has risen to ± 6 %. Similar ranges have been found in the Plastic Limits which, taken together with the uncertainties from the Liquid Limits, could give rise to significant concerns over using correlations based on the Plasticity Index. Other examples of results from various test methods are given in this paper and it is argued that much of the uncertainty comes not from the test method itself, but from other factors including basic equipment maintenance, calibration, technician training and competence. It will be seen that laboratory proficiency testing schemes are crucial in highlighting these problems and giving an opportunity to allow better assessment of the quality of both test results and, arguably, the laboratories that produce them.

Modelling the spatial variability of karstified processes in gypsum deposits – the case of a high-speed railway bridge in the Madrid Miocene Basin

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 10:55:43 +0200

The presence of karstification processes in the terrain poses a threat to the safety of the foundations of structures, which in the case of gypsum materials becomes more dangerous due to the rate at which they can progress. This work describes the case of a Spanish high-speed railway bridge whose route runs over a Tertiary gypsum formation belonging to the lower Miocene unit of the Madrid Basin. These are very firm materials in a healthy state, that allow the direct support of shallow foundations, which stand out for their high heterogeneity, with the presence of massive gypsum banks as well as alternating levels of gypsum and clay. However, these materials can be affected by karst processes of dissolution, weathering, and replacement by clays, in which case there is a marked degradation of their mechanical properties, and the eventual local appearance of cavities. In these circumstances, it is necessary to carry out soil improvement treatments, such as compaction grouting, or resort to deep foundations with piles that transmit the loads of the structure to a lower substrate in a non-disturbed state. By its nature, the detection of this type of processes by drilling rotary boreholes is not trivial, and there is often uncertainty associated with its spatial variability. This communication presents the results obtained after the execution of a geotechnical research campaign, consisting of the realization of seismic tomography borehole-profiles under each support of the viaduct, supported by the execution of conventional rotary boreholes. The results of this exploration have made it possible to understand and define the spatial extent of the materials degraded by karstification and the selection of robust foundation typologies that favour the sustainable and resilient nature of the infrastructure.

A Case Study for Data-driven Soil-layer Delineation

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 10:55:21 +0200

In the past, soil-layer delineation methods can usually only take a single type of input data, e.g., soil-type data at boreholes. However, this does not fit in the geotechnical engineering practice where multiple types of data are usually available during site investigation (e.g., borehole data and cone penetration test data are both available). This paper adopts a novel data-driven method for soil-layer delineation that accommodates multiple types of site investigation data. The basic idea is to include liquid limit (LL), plasticity index (PI), and fines content (FC) into the soil parameters of analysis. According to the Unified Soil Classification System (USCS), the information of (LL, PI, FC) can be used to determine whether the soil is sand, silt, or clay. As a result, the conditional random field simulation results for (LL, PI, FC) can be used to delineate sand, silt, and clay layers. If extra soil parameters (such as cone penetration test results) are incorporated, the novel method can accommodate multiple types of site investigation data. A real example of the Fucino Basin in Italy is adopted to demonstrate the application of the novel data-driven soil-delineation method.

A method to estimate the state parameter from CPTu soundings using Pocket G-PFEM

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 10:54:58 +0200

The state parameter is the main variable employed for predicting the undrained behaviour of artificial soils such as tailings and hydraulic fills. Current practice involves using screening methods and CPTu data (e.g. Robertson (2010)) or cavity expansion based methods (e.g. Shuttle and Jefferies (2016)). However, these methods have drawbacks: they are based on empirical correlations for clean sands and do not consider the effect of partial drainage. This paper presents a site-specific procedure to determine the state parameter of tailings, inspired in the work by Monforte (2022). The procedure consists of: i) calibrating the CASM constitutive model using triaxial tests for different state parameters; ii) determining the plausible range of hydraulic conductivity based on dissipation tests; and iii) conducting numerical simulations of CPTu tests using the Pocket G-PFEM tool for different combinations of state parameters and hydraulic conductivities. By comparing the results of the simulations with the real CPTu data, a site-specific relationship between the state parameter and the CPTu measurements can be established. To validate the procedure, the method is applied to a real tailings deposit and contrasted against routine screening methods. In the particular case studied in this paper, the method predicts more contractive behaviour than the screening methods. While the method is still in an early stage of development, it looks very promising because it allows for using the raw CPTu data to calibrate a constitutive model, without resourcing to any kind of correlations or empirical transformation models.

On the Probability of Boulder Encounters for Piles Driven in Glacial Till

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 10:54:36 +0200

Considering that a large part of Sweden is covered by glacial till, which is classified as an unsorted sediment formed by glaciers that can contain fragments of rock known as boulders, driving piles constitutes a substantial economic risk. Piles driven into glacial till may encounter boulders and undergo structural damages leading to premature refusal and to the loss of piles. Even though geotechnical investigations as of today form a solid basis for the design of pile foundations, the unpredictable presence of boulders and their hard resistance to breakage, makes it challenging to penetrate boulders by standard investigation methods. Currently, the only available source of information used by the Swedish construction industry to confirm the existence of boulders is a dynamic penetration test known as soil–rock sounding. Relying on the results from only one testing method may for most projects underestimate the existence of boulders and their potential impact to piles, leading to an unsuitable design of the entire piling system. This paper discusses the benefit in using the input from soil–rock soundings for quantifying the probability of boulder encounters in glacial till based on Poisson point process.

An Elaborate Seismic Study of Beirut: Integrating 3D Multidisciplinary Geotechnical Model Definition, Machine Learning Enhancements, and Numerical Simulations

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 10:54:13 +0200

In seismic hazard assessment, reliance on Vs30 proxies and 1D shear wave velocity profiles often leads to underestimated ground motion. This is particularly evident in areas with complex geological structures, such as Greater Beirut (GB). The metropolis, situated near active seismic faults, experienced significant nearby earthquakes in 551, 1202, and 1837. It is characterized by diverse soil compositions, that vary from sandy terrains to limestone formations, demanding a detailed geotechnical model for seismic hazard studies. Our research developed a comprehensive 3D geotechnical model for GB, integrating data from around 500 boreholes, 700 geophysical measurements, refined DEM, and geological insights. The model delineates variations in bedrock elevation and geological strata, some sites exhibiting sediment depths up to 80 meters. We performed an iterative data analysis by combining the horizontal to vertical spectral ratio method (H/V measurements) with borehole data. This approach enabled us to estimate the average shear wave velocity (Vs-mean) in the sedimentary layer and the depth of the bedrock across the model. To address data gaps in southern GB, we used a Random Forest machine learning model, trained on interpolated points from Kriging in the central model part, ensuring continuous representation of sedimentary units even in data-limited areas. Ongoing work involves seismic simulations predicting ground motion amplification in Beirut. Using a 3D hexahedral mesh generated via Python code, we will conduct full 3D numerical simulations of seismic wave propagation. These simulations aim to provide insights into Beirut's seismic response, contributing to earthquake preparedness and risk mitigation. We will present preliminary results in predicting the seismic motion in Greater Beirut using SPECFEM3D, a spectral-element method software designed for 3D seismic wave propagation simulations.

Material Subgrade Variability In Site Characterisation

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 10:53:10 +0200

Delineation of areas into a “uniform” harvestable quality material is required for cut and fill earthworks projects. Mixing or inadvertent contamination with onsite high-quality material with adjacent poor quality is unacceptable. Importing material from off-site sources have significant cost associated. Two case studies are presented to highlight the design and contractual interpretation of a “unform” site. The first case study compares when a characteristic design value is used versus the day to day on site requirements to meet these design requirements. The required coefficient of variation (COV) of material parameters is discussed from both a design and construction perspective for section delineation. A major highway road widening had 4 sections as part of the upgrade. The tender documents were based on balanced cut to fill. On site material variability had pockets of good and bad material. Statistical analysis pre and post tender were compared in the contractual dispute which followed. The contractor was obligated to then import material to significant subgrade depths for these sites. To do otherwise would be contra to both the design material requirements specified in the contract documents and the requirements of the Earthworks specifications. The second case study is for a major 13 km rail upgrade to illustrate how the COV can be used in site characterisation and spatial variation at a cutting. The COV values adopted for both design and construction assessment are different as the intent is different. A quality control COV is different for a characteristic design COV.

Geotechnical characterization using geophysical tests in areas of high geological complexity and landslides for horizontal directional drilling design

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 10:52:11 +0200

In August 2021, landslides occurred on the slope of the Cortinas sector over an area of more than three kilometers, which affected electrical towers, a national vehicle highway, an oil pipeline and a gas pipeline. Currently, these infrastructures have limitations in their operation, generating significant economic losses and therefore, in the case of the gas pipeline, the construction of a HDD of two thousand meters in length at depths of up to one hundred meters is proposed, with the purpose of being able to bypass the zones unstable and restore transportation to normal conditions. The design and construction of said work constitutes a challenge, since the project area has very special geological conditions, since the hillside deposits are very susceptible to failure and there is apparently a stress tensor of an active fault that directly affects the stability of the area. The projected HDD crosses a ravine and a slope with steep topography with difficult access, as well as different layers of sedimentary rock with intercalations, which are folded and highly fractured and saturated with water. These special conditions generated difficulties and opposed the completion of several attempts by other HDDs, but taking into account that this alternative constitutes basically the only solution from a technical point of view, it was necessary to carry out some borehole and multiple seismic geophysical tests and geoelectrical that would allow defining a detailed stratigraphic profile to be able to analyze the constructive feasibility and, in such case, the most appropriate method, as well as the geomechanically characterization of the rocks, since according to the numerical modeling they indicate that the stability of the drilling may be affected due to plasticization at its limits, with detachments of rock fragments and jamming of the tools necessary for its construction.

Determination of rock foundation levels for the expansion of the Cañaveral shopping center from geophysical tests and its correlation with direct exploration

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 10:51:11 +0200

The Cañaveral shopping center is located on a low slope formed by recent alluvial deposits of low consistency, supported on sedimentary rock of the Girón formation, which is found at depths that change abruptly between one and twelve meters in short distances, influenced by the presence of a geological fault line and processes of erosion and weathering by subway water currents. Considering that the loads on the foundation are of great magnitude, it is necessary to build about 100 deep caisson foundations to reach the rock. However, performing a borehole on each one of them represented a very high cost and long execution times that would generate discomfort in the operation of the warehouse. Therefore, an alternative was proposed to determine the depth levels of the rock through different geophysical tests of seismic lines and electrical tomography and try to calibrate the results through the correlation of some boreholes. During the execution and data processing phase of the geophysical tests, difficulties were encountered due to the level of environmental noise and the obtaining of the wave records, given the variability of the rock levels and even the effect that in some sectors of the study area the rock is very sub-surface. In conclusion, it was possible to identify the strengths and weaknesses of each of the exploration methods and generate a 3D map of the depths of the rock levels that served as input for the design and budget of the foundations, which were verified by constant supervision during construction and thus be able to determine the error percentages, as well as to present recommendations for future works where it is intended to use this type of techniques

Multivariate Gaussian Process for 3D subsurface stratigraphy prediction from CPT and labelled borehole data

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 10:50:49 +0200

Quantifying uncertainties in subsurface properties and stratigraphy can lead to better understanding of the ground conditions and enhance the design and assessment of geotechnical structures. Several studies have utilized Cone Penetration Test (CPT) data and employed Bayesian and Machine Learning methods to quantify the geological uncertainty, based on the Robertson’s soil classification charts and the Soil Behaviour Type Index (Ic). The incorporation of borehole data can reduce the stratigraphic uncertainty. Significant challenges can arise, however, mainly due to the intrinsic differences between field and laboratory-based soil classification systems, which can potentially lead to inconsistent soil classification. To this end, this study proposes a multivariate Gaussian Process model that utilizes site-specific data and: i) jointly models multiple categorical (USCS labels) and continuous (Ic) variables, ii) learns a (shared) spatial correlation structure and the betweenoutputs covariance, and iii) produces two types of dependent classification outputs. The results indicate that the integration of geotechnical and geological information into a unified model can provide more reliable predictions of the subsurface stratification, by allowing simultaneous interpretation of USCS and Ic profiles. Importantly, the model demonstrates the potential to integrate multiple variables of different types, aiming to contribute to the development of a methodology for joint modeling of geotechnical, geological and geophysical data.

Development of liquefiable zone mapping using semi-empirical methods

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 10:50:30 +0200

One of the most significant processes in soil dynamics is liquefaction. It is a loss of strength coupled by a quick increase in pore pressure, causing soil particles to break apart for a brief period. There have been several approaches published for calculating the residual or liquefied shear strength of cohesionless soils. This article gives cone penetration test relationships for assessing vulnerability to loss of strength and liquefied shear strength in a variety of soils. Then, based on the results of our studies, we were able to map the liquefiable zones of the Mnasra region, located in the Gharb basin and extending over an area of 4000 km2, which is characterized by two main facies: (i) a predominantly gravelly and/or conglomeratic facies, separated by silt-clay levels (east of the nappe), (ii) a predominantly sandy, sandstone and calcareous facies, separated by silt-clay levels (coastal zone and southern sector on the Maâmora side). IPL calculations predict a spatial-temporal variation in liquefaction at depths ranging from a low probability of liquefaction to a certainty

A Numerical Study on Effect of Site Conditions on Connection Load in Geosynthetics-Reinforced Soil Wall

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 10:50:14 +0200

Geosynthetics-reinforced soil (GRS) walls have gained immense popularity among other reinforced soil walls. In recent times, case studies have highlighted several GRS walls facing problems such as cracking on the facia, breakage of connection pins in the segmental block, breakage of connection between facia and reinforcement, and relative settlement between facia and backfill, all leading to the serviceability issues or failure of the wall. The existing design methods estimate connection loads using laboratory pull-out tests, which do not incorporate the effect of on-site conditions, such as differential settlement, compaction-induced stresses, and facia geometry, and the stress mobilization in the connection system. This study examines the stress distribution in the facia connection system of segmental reinforced soil walls subjected to site conditions such as inadequate backfill compaction and differential settlement between facia and backfill. A finite element (FE) approach has been adopted to predict the stresses in the reinforcement for the connection loads in the reinforcement-facia connection system subjected to the above-mentioned conditions. The modular block facia, along with geogrid reinforcement connections, was studied, incorporating appropriate geometrical and interface properties (viz. geosynthetics-block interfaces). Based on the study, the obtained variation in the von Mises stresses in the geogrid, embedded in the modular block, due to connection load at the service state was analysed. A comparative analysis of the performance of three different segmental block facia-reinforcement connections was also performed to understand their suitability in a particular site condition

Shear Wave Velocity Derived from Cone Penetration Tests In Clayey Soil Layers

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 10:44:05 +0200

Based on Cone penetration tests (CPT) data, a number of soil’s physical and mechanical parameters can be interpretated, like shear wave velocity, etc. Even though various studies have been conducted and methods are proposed, uncertainties still exist and the applicability of each method needs be further clarified. A case study on the interpretation of CPT results is performed which based on the measured data from an offshore site close to East Sea, China. This paper focus on clayey soil layers and presents an assessment of CPT data interpretation methods for the derivation of clayey soil’s shear wave velocity. It shows that Long’s method proposed in 2010 (C1) and Cai’s method proposed in 2014 (C2) provide better predictions of shear wave velocity. Additionally, values of soil unit weight used in the shear wave velocity derivation can also be interpretated from CPT data since it shows ignorable effect on the interpretated velocity profile.

Numerical study of viscous effects during CPTu

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 10:43:41 +0200

Variable penetration rates during CPTu may impact cone readings through partial consolidation during penetration but also through viscous soil skeleton behaviour. The latter phenomenon is characteristic of dynamic penetrometers during fast penetration in fine-grained materials where tip resistance increases when the penetration rate increases. In this work, the effect of viscosity on piezocone penetration is investigated based on the numerical simulation of CPTu and triaxial tests using the application G-PFEM and a viscoplastic version of the Clay and Sand Model (CASM). The study highlights that the CPTu results are sensitive to the material parameters controlling viscosity, thus requiring careful calibration in order to obtain realistic CPTu simulations.

Prediction of Land Surface Subsidence in the U2 Metro Tunnel in Vienna

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 10:43:21 +0200

Availability of artificial neural network for Estimation of Consolidation Properties of Holocene Clays in Osaka Bay

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 10:43:02 +0200

In this study, artificial neural network, a popular machine learning technique, was used to estimate the consolidation properties of points where no soil investigations have been conducted. The Holocene clay layer at the construction site of Kobe Airport, a large-scale man-made island in Osaka Bay, was targeted to estimate the consolidation properties. The performance of an estimation model built with artificial neural network depends on the datasets used during the training phase. Therefore, the average of multiple estimation results can be used. Numerical simulations using the estimated consolidation properties can accurately reproduce the settlement behavior owing to reclamation during the construction of Kobe Airport. Artificial neural network can easily and objectively estimate the consolidation characteristics of any point based on the existing soil investigation results.

A Case Study on Quantile and Percentile Regression to Select Design Lines for Complex, Real Work Profiles

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 10:42:26 +0200

Site characterisation necessarily relies on engineering judgement, usually combined with some level of statistics to define characteristic values for design purposes. A suitable method for this task is quantile regression, which allows for the definition of lower, upper, and best-estimate characteristic values. The application of quantile regression to homogeneous profiles is relatively straightforward. Although such sites are common in some areas, there is need for a more comprehensive approach to quantile regression that covers the more general scenario of heterogeneous stratified profiles. This paper takes piezocone penetrometer data from a relatively complex seabed site and demonstrates the streamlined application of quantile regression, highlighting and analysing some of the assumptions and choices behind the approach. The work shows the nuances of the method and suggests workarounds for potential scenarios where its application may be challenging.

Effect of clay activity and interface surface material on residual undrained interface strength: implications on pipeline-seabed interaction analysis

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 10:41:27 +0200

Characterization of the geomechanical behavior of the seabed along a high-pressure high-temperature (HPHT) pipeline route is important for understanding risks from geohazards and thermally induced displacements such as axial walking. Axial resistance to pipeline displacement, from the friction between seabed and the contact surface of the pipe, can be estimated through laboratory tests using interface shear box (ISB) and tilt table. Tests performed by NGI in several developements in Gulf of Mexico, South America, and West Africa revealed significant variation in shear resistance, potentially associated with the type of interface material and surface roughness characteristics. This paper illustrates the effect of clay activity and interface surface material on the residual undrained interface strength estimated from interface shear box tests. Two cohesive soil batch samples with varying activity were tested using two different interface plates (steel and silicon carbide sandpaper) of comparable surface roughness. Each soil batch-interface combination was tested under three different initial effective normal stresses and two different over consolidation ratios (OCRs). Undrained residual interface strength envelopes were developed for each soil batch-interface combination. The results from tests performed on steel interface showed an increase in residual undrained interface strength with plasticy and clay activity whereas a reverse trend was observed in the results of the tests performed using the sandpaper interface. This reinforces the importance of the choice of interface plate material (in addition to surface roughness) for PSI testing program to accurately capture the resistances offered by the seabed to pipe displacement.

Uncertainty Estimation on Active Surface-Waves Based Tests

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 10:40:31 +0200

Geophysical methods based on surface waves have become very popular in recent decades due to their versatility and reduced cost of execution compared to other invasive techniques. Due to space constraints in urban environments, measurements with linear arrays using active and passive techniques are usually combined to reach the exploration depth required by seismic site classification regulations. Although several good practice guidelines have been developed for performing this type of geophysical explorations, one of the remaining major challenges is to relate the results of these explorations to uncertainty metrics. In the case of active tests, there are effects associated with the filtering method used to eliminate the near and far-field effects, as well as other difficulties related to higher Rayleigh-modes or heterogeneities of the site. In this paper, we study the effect of body waves unavoidably induced in active tests on the proper determination of the dispersion curve of a site. For this purpose, active tests are carried out using triaxial geophones to extract from the records the motion effectively corresponding to Rayleigh waves by means of the Normalized Inner Product (NIP) technique. The results show that the effects of body waves are negligible for frequencies above about 8 Hz, but below this value, in the transition zone with ESPAC passive tests, the differences can be more significant. These results are used to introduce uncertainty indicators in this type of explorations

Record of long-term field observation of large-scale cutting slope

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 10:39:26 +0200

This paper describes the interpretation of landslide behavior and verification of the effectiveness of countermeasure works based on the results of long-term field observations at a large-scale cutting site. The site has been subjected to various deformations since its construction due to its unique geological conditions, and has been monitored extensively by GPS surface displacement gauges, borehole inclinometers, anchor load cells, and water level gauges as an important monitoring site even after it was put into service. In the sixth year after the site was opened to public use, we assumed underground slip surfaces based on an interpretation of the observed data, constructed additional countermeasures, and verified the effectiveness of the countermeasures through continuous field observation of intermittent landslide behavior observed in several areas of the slope. As a result, it was confirmed that the displacement had not been settled even five years after the construction of the additional countermeasures and that a new slip surface had emerged, indicating the necessity of improving field observation techniques and data interpretation as well as continuous monitoring of this site

Quasi-region-specific model uncertainties of simplified liquefaction triggering analysis

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 10:38:25 +0200

In earthquake-prone regions, assessing soil liquefaction potential is indispensable for contemporary seismic design. Various procedures for liquefaction triggering analysis have emerged over the past decades. However, most of them are derived from generic liquefaction databases, such that the model uncertainties in liquefaction potential assessments applied to a specific region of concern remain unknown, which poses a challenge for engineers to evaluate the liquefaction risks of target sites. This study aims to propose a hierarchical Bayesian model (HBM) to learn the inter-region characteristics of model uncertainties of the traditional simplified liquefaction potential evaluation methods based on a database containing global case histories of liquefaction categorized into several regions where those triggering events occurred. The learning outcomes can yield the model uncertainty of the target region, and the liquefaction probability at the target site under a given ground motion condition. For an illustration of the proposed model, a case history of liquefaction from a specific region is adopted to construct a quasi-region-specific model uncertainty and evaluate the liquefaction probability in the target soil. The illustration shows that the constructed quasi-region-specific model uncertainty with liquefaction histories in the target region can improve liquefaction occurrence prediction in comparison with the prediction without any histories, which is believed to benefit the engineering practice.

Statistical Uncertainty of Cyclic Resistance of Sand under Constant Volume Direct Simple Shear

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 10:37:25 +0200

In the design work of offshore foundations, such as monopiles and gravity platforms, the cyclic resistance of soil plays a critical role in assessing the effect of cyclic loading induced by wind, waves, and rotor dynamics during the operational lifetime. However, the cyclic behaviour of soil is often derived from only a limited number of laboratory tests, which can lead to inaccurate estimates of soil behaviour. Furthermore, this imprecision can affect the parameters selection for the design process. To gain a better understanding of the limitations and uncertainties associated with laboratory experiments, a series of cyclic direct simple shear (cDSS) tests are conducted on marine sand. Four combinations of consolidation stress and void ratio are selected, and a constant volume cDSS test is repeated a substantial number of times for each combination. This dataset captures the measurement uncertainty on the cyclic soil resistance. By analysing the variability of the results, the statistical distributions for the cyclic soil resistance parameters can be determined (e.g. number of cycles to reach a certain shear strain level). The same specimen exhibits slightly different strain-stress relationships due to the inherent variability of sand. Statistical methods are used to describe the cyclic resistance of the sand.

Comparative Assessment of the Vertical Scale of Fluctuation of Undrained Shear Strength of Clays From CPT and DMT Testing: a Case Study in Central Italy

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 10:36:31 +0200

The quantification of the spatial variability of soil properties allows the enhanced engineering modelling, analysis, and design of geotechnical systems. Evolutionary design codes such as Eurocode 7 are awarding spatial variability an increasing central role in geotechnical design. The spatial variability of geotechnical properties is often investigated using a random field approach. Among the defining parameters of a random field is the scale of fluctuation, which describes the extent of significant spatial correlation in a specific spatial direction. The scale of fluctuation can be estimated quantitatively using a variety of methods relying on statistical approaches. The scale of fluctuation is not an inherent property of a soil. Existing studies demonstrate its dependency from numerous factors including the spatial direction, measurement interval, and user-defined modelling options. This paper illustrates the procedures and main results of the comparative estimation of the vertical scale of fluctuation of undrained shear strength of a layer of silty clay from piezocone (CPTU) and dilatometer (DMT) testing at a rural site in the region of Tuscany in central Italy. Vertical scales of fluctuation were calculated using two methods available in the geotechnical literature. Quantitative estimates are compared and analysed critically.

Modeling and Characterizing Locally Subsiding Ground for the Analysis and Design of Mat Foundations

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 10:36:15 +0200

Mat foundations are often used as a means of protecting buildings and other structures from excessive distortion due to differential settlements in the underlying ground. Once soil bearing capacity concerns have been addressed, the analysis of these foundations becomes a soil-structure interaction problem where the bearing pressure from the mat induces settlement in the underlying ground while localized settlement distorts the mat and redistributes the bearing pressure. An accurate representation of this soil-structure interaction is necessary to facilitate computations of the shear and flexural stresses in the mat and to develop an appropriate structural design. However, modeling and characterizing this system has long been a source of confusion and contention among both geotechnical and structural engineers. The soil response is typically characterized using the modulus of subgrade reaction, ks (also known as the coefficient of subgrade reaction) which describes a certain mechanical soil-structure interaction model known as a Winkler foundation. However, ks is arguably one of the most misunderstood and misapplied parameters in geotechnical practice, and proper assessment of this parameter is more complex and nuanced than might be expected. Further complexities are introduced when locally subsiding ground is present. This is because the Winkler model assumes settlement occurs in the soil only in response to an applied bearing pressure, whereas local subsidence introduces additional settlement (with associated shear and flexural stresses in the mat) which is independent of that caused by the applied structural loads. Methods of modeling and characterizing the subsurface conditions for the purpose of developing design values of ks to be used in mat foundation analysis and design are proposed, then these methods are extended to accommodate sites with locally subsiding ground. These methods are compatible with standard geotechnical assessment techniques as well as standard structural analysis and design software packages.

Identification of random field for ground stiffness by data assimilation based on surface wave method and sounding tests

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 10:35:56 +0200

The surface wave method (SWM) and the screw weight sounding (SWS) are employed as a geophysical exploration method and a sounding test, respectively to identify the spatial distribution of the stiffness of an earth-fill dam in the present study. The ensemble Kalman filter (EnKF) is used as a data assimilation technique. It can estimate the spatial distribution of the Young’s modulus as the stiffness of an earth-fill dam by assimilating the travel time to the first arrival of the surface waves. By the ensemble data assimilation, the measured data from the SWM is applied to simultaneously estimate the Young's modulus and evaluate the uncertainties. The SWS results are employed as the prior information to generate the initial ensemble through the sequential Gaussian simulation (sGs). Proposed method has been applied to the actual data of the SWM and the SWS measured at an earth-fill dam site. Consequently, it has been clarified the proposed approach could identify the appropriate random field of Young's modulus.

Toward probabilistic ground models for time and cost estimation of tunnel projects

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 10:35:35 +0200

The construction time and cost of a rock tunnel project are highly dependent on the rock mass quality and encountered ground behaviour. In most rock tunnel projects, the knowledge about the ground conditions along the tunnel is limited, making it difficult to predict accurately the construction time and cost. The KTH model takes a probabilistic approach to address this problem; however, it does not account for the spatial variability of the ground conditions. This paper investigates an alternative probabilistic ground model to be used within the KTH model that enables accounting for the spatial variability through Markov random field theory. The new ground model employs a parametric approach to describe the properties of the Markov field, hence, enabling the simulation of the ground conditions with limited data, but does not consider the epistemic uncertainty in the model parameters. This will be the addressed in future research.

Data-Driven Simulation of Multivariate Cross-Correlated Geotechnical Random Fields from Sparse Measurements

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 10:35:18 +0200

It is widely acknowledged that many geotechnical properties are correlated over space and/or time. Consequently, crosscorrelated random fields play a pivotal role in geotechnical reliability analysis for properly modeling both the auto- and cross-correlation structures of correlated geotechnical properties. Existing methods for simulating cross-correlated random fields typically require precise knowledge of random field parameters as input. However, in a typical site investigation program, engineering constraints such as limited time, budget, and space often lead to sparse measurements of geotechnical properties. Estimating reliable random field parameters, particularly the auto-correlation and crosscorrelation structures of a two-dimensional (2D) cross-correlated random field, from such sparse data is a notorious challenge. To address this issue, this study introduces a 2D cross-correlated random field generator that can directly simulate 2D multivariate cross-correlated geotechnical random field samples (RFSs) from sparsely measured data points. This generator leverages the method developed by Guan and Wang (2023), which employs a joint sparse representation to simultaneously exploit auto- and cross-correlation structures of various spatial/temporal quantities directly from sparse measurements. The effectiveness of the proposed generator is demonstrated using real geotechnical properties data. The results demonstrate that RFSs generated using this method from sparse measurements accurately capture the spatial auto- and cross-correlation structures of different geotechnical properties.

Stratification identification and prediction of missing CPT data by Mixture of Gaussian Processes

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 10:35:00 +0200

Stratification identification and spatial interpolation play a fundamental role in geotechnical site characterization. A unified approach is needed to perform these two tasks simultaneously to reduce overall uncertainty in site characterization. This paper explores the applicability of the Mixture of Gaussian Processes (MoGP) to address this gap, with a specific focus on characterizing and completing missing CPT data. The investigation encompasses both synthetic and real-world field CPT datasets and includes a comparison of the MoGP's interpolation accuracy with the use of a single GP for entire datasets. Additionally, the study examines the sensitivity of the model's performance with respect to the number of training data points. Although the interpolation performance of the MoGP model is promising with synthetic data, limitations appear in its application to real-site CPT data.

SDMT VS profiles in heterogeneous granular soil deposits

Jesús Sánchez Pinedo — Fri, 07 Jun 2024 14:13:27 +0200

Many urbanized areas of the Apennines, in Italy, have complex soil stratifications. A typical example is the historical center of L'Aquila and its outskirts, founded on layers of significantly heterogeneity and struck by a strong earthquake in 2009. Under these conditions, shear wave velocity profiles (VS) obtained from in-situ measurements using SDMT techniques allow reliable analyses of local seismic response. In the soil of L'Aquila, the use of SDMT tests in sand-filled boreholes, following the procedure described by Totani et al. (2009), allowed VS to be measured at considerable depths. This article presents the results of local seismic response analyses conducted to characterize the soil foundation of the hospital complex and adjacent university buildings in L’Aquila before their seismic retrofitting. The authors developed a soil model based on the Vs profiles retrieved from the SDMT tests. This approach provided a detailed understanding of the soil seismic behaviour, essential for the proper characterization of seismic action and consequently, the design of seismic interventions. The study emphasises the importance of accurate soil characterisation prior to seismic upgrades especially in deposits where there are multiple shear wave velocity inversions. The seismic demand coming from the Italian Building Code of 2018, based on the so-called soil categories from equivalent velocity of shear wave, was compared to the results of the local seismic response analysis conducted by using the real Vs profiles from SDMT, which are extended to a much greater depths than those generally required by the regulations.

Compacted Landfill Quality Based on DMT

Jesús Sánchez Pinedo — Fri, 07 Jun 2024 14:12:29 +0200

For the last 25 years we have been using DMT tests to check the quality of landfill compaction. In several situations of large areas subject to earthmoving, significant pathologies were observed associated with the occurrence of settlements, determined by poor compaction of landfills. These settlements affect the internal floors of buildings, external floors, and sometimes the foundations also. With the intense use of the DMT test as an usual geotechnical investigation practice, it was possible to group the results of these tests, separating them into cases of good, average, and bad behavior. With these systematic observations, it was possible to adapt the traditional graphical representation proposed by Silvano Marchetti and David Crapps, relating the material index "Id" with the dilatometer modulus "Ed", creating regions that represent well-compacted landfills, those with medium compaction and poorly compacted landfills. This system makes it easy to predict the settlement behavior of compacted landfills and represents an appropriate method for checking the quality of compaction.

Site Exploration for Anchoring of Wave Energy Converters

Jesús Sánchez Pinedo — Fri, 07 Jun 2024 14:11:27 +0200

Wave energy converters (WECs), a form of marine hydrokinetic (MHK) energy device, transform the mechanical energy of water waves into electricity. They are typically held on station using anchoring systems embedded into the seafloor sediments (as opposed to, e.g., concrete gravity anchors). The design of WEC anchors is particularly challenging for two primary reasons: (1) WECs are often deployed in previously undeveloped areas of the ocean, so the engineering properties of the seabed are largely unknown; and (2) the economic margins on wave energy are quite thin, so heavily overdesigned anchor systems in response to data sparsity are not feasible. This paper describes the planning, execution, and outcomes from a dedicated in-situ testing campaign informed only by limited geophysical data a priori. A series of 22 cone penetration tests (CPTs) were performed at a 7-km2 site approximately 11 km off the United States’ west coast. Water depth was up to approximately 75 m and the target depth for the cone soundings was 10.5 m below the seafloor. Measurements indicated that much of the site subsurface consisted of dense sand and gravel, though tests identified an overlying softer layer in some parts of the site. A summary of lessons learned and recommendations for future explorations at similarly unexplored sites are provided.

Continuous Medusa DMT tests in a very soft clay

Jesús Sánchez Pinedo — Fri, 07 Jun 2024 14:10:29 +0200

The dilatometer test (DMT) has been shown very useful in providing a number of geotechnical parameters, in different types of soils. The test is regularly carried out every 0.20 m, i.e., it is a discontinuous test. Therefore, its capability of detecting variations in the geotechnical profile is conditioned by the tests interval. The Medusa DMT, however, is able to obtain continuous measurements of the A-pressure reading, thus providing a much better picture of the soil stratigraphy. Medusa DMT tests have been carried out at Sarapuí II very soft clay deposit around Guanabara Bay, in Rio de Janeiro, and a detailed soil profile was obtained. A comparison was made with piezocone tests. The stratigraphy of the deposit obtained by both tests was almost the same.

Soil liquefaction assessment of Ecuadorian coastal region using SDMT test (Puerto Baquerizo site)

Jesús Sánchez Pinedo — Fri, 07 Jun 2024 14:09:30 +0200

On March 18, 2023, a Mw6.6 earthquake hit the South Guayas coastal region (Ecuador), resulting in human fatalities and extensive structural damage. The event triggered widespread soil liquefaction evidences by significant volume of ejected material, which persisted several weeks following the event, marking the epicentral area prone to liquefaction. To assess the susceptibility to seismic-induced soil liquefaction, we performed one seismic dilatometer test (SDMT) in an area where the phenomenon clearly manifested. This study aims to evaluate and compare various established SDMT methods for predicting soil liquefaction potential under the specific 2023 seismic event. The findings are expected to enhance the understanding of liquefaction and contribute to improve seismic hazard assessment in areas along the Ecuadorian coast, which are often interested by earthquakes, as well as to the development of mitigation strategies in this earthquake prone coastal region.

Characterisation of Carse Clays Using Seismic DMT

Jesús Sánchez Pinedo — Fri, 07 Jun 2024 14:08:28 +0200

The estuarine sediments around the head of the Forth estuary deposited during and after the Flandrian interglacial are an important, economically productive regional soil horizon in Scotland. The soil has been extensively studied locally (Hight et al., 1992) at the Bothkennar EPSRC site however, to the authors’ knowledge seismic dilatometer testing using Marchetti’s Medusa apparatus has never been used to characterise the material. Taking data from a number of sites and using an automated Medusa seismic dilatometer apparatus, a complementary contribution to the characterisation of the site which includes some comments on spatial variability of the material and other observations are presented.

Comparative Analysis of DMT, CPTt And DPH for Soil Characterization of Granular Rhine Soil

Jesús Sánchez Pinedo — Fri, 07 Jun 2024 14:07:27 +0200

This paper presents the results of direct and indirect field investigations carried out as part of a detailed soil investigation of granular Rhine soil in Germany. After a brief overview of the project and geological conditions in the project area, the results of the field investigations are shown in a compressed and comprehensive manner. Focus of the presented results are the DMT, which are a novelty for projects in Germany. The presented results clearly indicate the challenges regarding the interpretation of the test results in the mainly dense to very dense sands and gravels, as especially the results of the DMT tend to scatter a lot. Despite the interpretation challenges, a comparative analysis of the CPT and DMT is carried out showing possible relations between dilatometer modulus Ed, friction angle DMT , corrected cone resistance qt and relative density ID. The relations are discussed, and limitations are presented. Afterwards, a strength-based correlation between CPT and DMT to determine the effective friction angle as a function of the cone resistance is presented indicating reasonable results for the investigated soils in the project area. The paper finishes with a discussion of limitations of the DMT and conclusions.

A novel strategy to digitalize, integrate and analyse data for the characterisation of landslides in turbiditic deposits

Jesús Sánchez Pinedo — Fri, 07 Jun 2024 14:06:30 +0200

A phenomenological interpretation of the slope factors and lanslide mechanism represents the first stage for the assessment of landslide hazard at the slope scale. This requires processing, analysing and integrating a large set of multidisciplinary and heterogeneous data, obtained through diverse activities, among which: geological and geomorphological studies, geotechnical investigations and monitoring, topographic and structural damage surveys. The integration of such a variety of multisource data, to build up a sound conceptual model of the slope, can be particularly challenging, especially in geohydromechanical contexts characterised by a great spatial variability of soil properties and complex hydraulic boundary conditions, such as in the case of slopes composed of turbiditic formations. This paper presents a new methodological approach for the study of landslide hazard at the slope scale, based on the combined use of an open-source GIS platform and an in-house developed dashboard for the interactive visualisation and analysis of geotechnical laboratory data. The details of the GIS project and the potentiality of the data-analysis dashboard are described, highlighting the interoperability between the two digital tools. The proposed methodology is applied to a pilot site, the Pianello area in Bovino, in the souhteastern Apennines, a widely investigated hillslope composed of tectonised clayey turbidite, hosting a complex basin of slow-moving landslides.

Dynamic properties of the Holocene age deposit in the Italian port of Ravenna

Jesús Sánchez Pinedo — Fri, 07 Jun 2024 14:05:30 +0200

Based on the collection of many data coming from a large survey carried out in the Ravenna Port channel, this paper focuses on the dynamic properties of the 30 m thick soil deposit whose poor geotechnical characteristics make the design of infrastructures in the area particularly challenging. The study included specific seismic in-situ investigations (e.g. Seismic CPTu and CH), laboratory tests on undisturbed bored samples (e.g. Resonant Column Test) and common in-situ testing (e.g. CPTu, DMT). The main objective is the estimate of the very small strain shear modulus and its decay with strain level (i.e. curves G0-gamma) for dynamic characterization. This is a fundamental aspect to consider for numerical modelling of geotechnical engineering problems considering soil-structure interaction under working loads and site response analysis. The availability of direct and indirect measurements of the dynamic soil properties allowed the comparison between the different estimates and an evaluation on the applicability of the correlations between the outcomes from possible in-situ investigations.

Effect of the fines content on the seismic response of a liquefiable deposit based on dilatometer tests

Jesús Sánchez Pinedo — Fri, 07 Jun 2024 14:04:28 +0200

In the simplified methods for estimating the cyclic resistance ratio (CRR) based on the flat dilatometer test (DMT), the liquefaction triggering curve is defined as a function of the horizontal stress index. A DMT-based calibration of a simplified pore water pressure model for effective stress analyses has been also recently proposed by Chiaradonna et al. (2023), even though limited to an ideal clean sand. This paper aims to explore the effects of the fines content on the seismic response of a liquefiable site where the cyclic strength of the soils is estimated by dilatometer tests. This evaluation is firstly performed on an ideal one-dimensional soil column, where the percentage of fines content is parametrically changed. Then, the study is verified on a real case, by considering a well-investigated site located in the Emilia-Romagna plain (Italy), where widespread liquefaction occurred in the 2012 seismic sequence. Indeed, a comprehensive site characterization from previous in-situ and laboratory tests carried out by various research groups is available for sand, silty sand, and sandy silt deposits encountered in that area. The nonlinear dynamic analyses accounting for the fines content effect are compared with that obtained by adopting the calibration procedure based on laboratory tests. Guidelines and limitations of the proposed approach obtained from this study are useful in providing awareness to practitioners about the calibration strategies for dynamic analysis based on DMT-tests.

Combined use of cptu-sdmt and geophysical test to assess liquefaction: case studies in Emilia-Romagna (Italy)

Jesús Sánchez Pinedo — Fri, 07 Jun 2024 14:03:32 +0200

The presence of a non-liquefiable crust overlying a liquefiable layer plays a significant role in determining the occurrence of liquefaction damage, as originally formulated by Ishihara in 1985. Following the 2010-2011 Canterbury seismic sequence (New Zealand), almost no foundation deformation occurred in areas characterized by soils susceptible to liquefaction overlaid by at least 3 m-thick intact crust. In contrast, the 2012 Emilia-Romagna earthquake (Italy) provided evidence of liquefaction in silty-sandy layers below 3 to 9 m-thick crusts. Therefore, Ishihara’s approach and the variety of liquefaction severity indices need to be further tested to assess to what extent they can be considered reliable predictors of performance. This study aims at better understanding the role of non-liquefiable crusts in preventing damage to buildings and infrastructures. In this respect, in situ and laboratory tests were conducted at selected sites in EmiliaRomagna. The results of two case studies in Mirandola (Modena, Italy), which share similar soil profiles but exhibited different liquefaction evidences following the 2012 seismic sequence, are presented. Comprehensive geotechnical and geophysical surveys were performed at both the sites, by means of piezocone tests, seismic dilatometer tests, boreholes, laboratory tests, electrical resistivity tomography and multichannel analysis of surface waves. These surveys document the geotechnical and geophysical properties of the 5 m-thick non-liquefied (or potentially non-liquefiable) crust and of the liquefied (or potentially liquefiable) silty-sandy deposits. This effort is aimed at understanding how the surface layer properties contributed to the different behavior observed at the two sites during the earthquake events.

Comparison of Pore Pressure Parameters from Piezocone and Dilatometer

Jesús Sánchez Pinedo — Fri, 07 Jun 2024 14:02:27 +0200

The Piezocone (CPTU) and the Marchetti Flat Plate Dilatometer (DMT) provide a number of empirical correlations for the purpose of soil identification. Each tool has defined a pore pressure parameter. For the piezocone, the parameter Bq ‘is based on the penetration pore pressures, the corrected tip resistance, the total overburden stress, and the existing hydrostatic pore pressure. This index has been used to characterize soil behavior rather than the actual soil type. For the dilatometer, the parameter Ud is based on the corrected pressures p0 and p2, calculated using the A and C readings and the existing hydrostatic pore pressure. This index can be combined with the material index ID to help with soil identification. Results from several test sites provide a promising direct correlation between Bq and UD, which can be used to enhance the identification of soil types by simply using the C-reading when performing DMT tests. Although the C-reading has been grossly ignored by users of the DMT, this new development will encourage measurement of this reading which provides similar trends to the pore pressures measured by the CPTU. The latest DMT equipment allows for the automatic measurement of the C-reading, which will assist in developing and enhancing existing correlations. This paper will present results at test sites located on opposite coasts of the USA. The trends of the Bq and UD indices are shown to be remarkably similar in all types of soils.

The JELLYFISh Project: Medusa SDMT testing at the NGTS Geo-Test sites, Norway

Jesús Sánchez Pinedo — Fri, 07 Jun 2024 14:01:59 +0200

This paper presents an overview of the experimental activity and the main results obtained as part of the Transnational Access project – JELLYFISh funded by H2020-GEOLAB. The project is based on an extensive in-situ testing campaign with the Medusa SDMT, the newest fully automated version of the seismic dilatometer (SDMT). The campaign was carried out in June 2022 in different soil types at four well-known benchmark test sites in Norway: Halden (silt), Onsøy (soft clay), Tiller-Flotten (quick clay), and Øysand (sand). These benchmark sites, largely documented in previous research, are part of the Geo-Test Sites (NGTS) research infrastructure managed by the Norwegian Geotechnical Institute. The paper includes: (i) highlights of the JELLYFISh project, (ii) a brief description of the Medusa SDMT main features, (iii) a summary of the field testing program at the four sites, (iv) a comparison of the results provided by Medusa SDMT using alternative test procedures and by traditional (pneumatic) SDMT and (v) conclusions. The results of the project highlight that, due to improved accuracy of pressure measurements and controlled pressurization rate, the Medusa SDMT has the potential for providing significant advancement in soil characterization compared to the traditional SDMT technology. These capabilities are particularly useful when investigating soft clays (e.g., Onsøy) in which the measured pressures are typically very small, intermediate soils (e.g., Halden) in which non-standard test procedures using variable penetration/pressurization rates may be easily implemented, or sensitive clays (e.g., Tiller-Flotten) in which alternative test procedures may provide guidance for distinguishing quick and non-quick clays.

Soil Behavior and Shear Strength Parameters of an Organic Alluvium Soil Using the CPTu and DMT

Jesús Sánchez Pinedo — Fri, 07 Jun 2024 14:00:28 +0200

The evaluation of in-situ behaviour, strength and compressibility of a soil profile is routinely performed by geotechnical engineers through field tests, such as the seismic piezocone penetration test (SCPTu), the flat dilatometer test (DMT) and the field vane shear test (FVT). This paper aims to compare the results of a CPTu, DMT and FVT to evaluate an organic alluvium soil in terms of: i) in-situ soil behaviour classification, ii) undrained shear strength and iii) stress history. To compare and complement the in-situ results, laboratory tests were carried out to determine the grain-size distribution, the Atterberg Limits, the pre-consolidation pressure, the organic content and the undrained shear strength under isotropic consolidation triaxial test (CIUC). The results showed that the soil evaluated herein exhibited a clay-like behaviour based on the classification system of both tests (DMT and SCPTu), which agrees with the laboratory characterization. Furthermore, the OCR (overconsolidation ratio) calculated from the SCPTu and DMT also shows a convergence with the values determined from laboratory tests. The SCPTu performed in this soil was predominantly undrained and enabled the calculation of undrained shear strength. Based on this, the methodologies based on Nkt and N∆u (from SCPTu) were compared with the undrained shear strength from the FVT and that obtained from DMT, based on the KD parameter. Finally, a comparison is presented to discuss the influence of shear mode in the undrained shear strength and the applicability of the methodologies used to evaluate the soil behaviour and the stress history.

Experimental Study of DMT Blade in Sand Using Particle Image Velocimetry

Jesús Sánchez Pinedo — Fri, 07 Jun 2024 13:59:29 +0200

In the study of geotechnical problems, numerical methods such as finite and discrete elements are progressively more used, sometimes overlooking experimental studies. Therefore, this work emphasizes the importance of physical experimentation, applying a digital image correlation (DIC) methodology. For this research, particle image velocimetry (PIV) was chosen using the GeoPIV-RG software. A model replicating the geometry of a full-scale DMT blade was used to evaluate its impact. An experimental setup was designed and built to recreate the driving of this geometry in dry and loose Bío-Bío sand, recording the process through photographs for analysis by PIV. Results show cumulative displacements, displacement patterns according to depth, and analysis of incremental shear deformation. A displacement direction analysis was carried out. It is concluded that the displacement pattern generated by its driving corresponds to an angle much smaller than what is reported for the CPT, and the incremental shear strain does not exceed 2% during the driving process.

The use of SDMT Data for Local Seismic Response Studies in the Catania Area

Jesús Sánchez Pinedo — Fri, 07 Jun 2024 13:58:30 +0200

Soil stiffness at small strain is a key parameter to solve many geotechnical problems, such as the design of the foundation and the knowledge of the seismic behaviour. There are many methods to perform in-situ soil shear wave velocity measurements: Down Hole test (D-H), Cross Hole test (C-H), Spectral Analysis of Surface Waves (SASW), Multichannel Analysis of Surface Waves (MAWS), etc. Among these methods, the use of Seismic Dilatometer Marchetti Tests (SDMT) to measure the shear wave velocity profile was developed and used in Italy. This test shows good repeatability of the measurements and the possibility to know, at the same time, the mechanical soil characteristics in the static field. In order to evaluate the soil profile of shear wave velocity (Vs), deep site investigations have been undertaken in some Italian sites, prone to high seismic risk. C-H and D-H tests, SDMT and Noise Analysis Surface Waves (NASW) have been carried out. In this paper, the relevance of using the Seismic Dilatometer Marchetti Tests (SDMT) as a basic tool for a comprehensive soil site characterization to carry out a local seismic response study was analyzed.

Analysis of DMT Results and Comparison with Other In Situ Tests in a Sensitive Clay of Eastern Canada

Jesús Sánchez Pinedo — Fri, 07 Jun 2024 13:57:27 +0200

This paper presents a re-evaluation of test results obtained from an extensive series of in-situ tests carried out in a lightly overconsolidated sensitive clay of eastern Canada. The geotechnical investigation involved self-boring pressuremeter tests (SBPMTs), flat dilatometer tests (DMTs), hydraulic fracture tests (HFTs), and vane shear tests (VSTs). The first surprising result is that the in-situ coefficient of lateral pressure at rest, K0, deduced from DMTs, SBPMTs, and HFTs is much higher than expected. Second, the values of the overconsolidation ratio, OCR, computed from DMT data are also much higher than oedometer-deduced values. Third, undrained shear strengths obtained from SBPMT expansion curves are higher than both DMT- and VST- deduced values, with the latter tests yielding very similar results.

Comparative Assessment of DMT-Based and CPT-Based Transformation Models for the Estimation of Shear Wave Velocity: a Case Study in Central Italy

Jesús Sánchez Pinedo — Fri, 07 Jun 2024 13:56:29 +0200

The definition of the shear wave velocity profile is a fundamental step for the seismic characterization of a site in the context of Eurocode 8 and for the conduction of earthquake geotechnical engineering efforts such as site response analysis. Shear wave velocity profiles can be obtained: (1) directly from seismic geophysical and seismic geotechnical tests; or (2) indirectly, from “static” in-situ geotechnical tests such as dilatometer tests (DMT) and cone penetration tests (CPT). In the latter approach, shear wave velocity is estimated by using transformation models which are typically derived from data collected at other sites. This paper illustrates the procedures and main results of the comparative assessment of the performance of existing DMT-based and CPT-based transformation models to estimate shear wave velocity at two adjacent spatial locations in a rural site in the region of Tuscany in central Italy. Model-predicted shear wave velocity profiles were compared with direct measurements obtained by geophysical seismic dilatometer (SDMT) testing. The comparative assessment involved the definition, calculation, and assessment of quantitative performance statistics. The paper provides a critical analysis and a discussion of the outcomes with respect to soil type.

DMT-based liquefaction assessment accounting for the fines content effect: a case study Emilia-Romagna italy

Jesús Sánchez Pinedo — Fri, 07 Jun 2024 13:55:28 +0200

Simplified methods for seismic liquefaction assessment based on the flat dilatometer test (DMT), in which the liquefaction triggering curve is defined based on the horizontal stress index (KD), have been proposed over the years. One major drawback of the existing methods, valid for clean sand, is the lack of a correction factor for the fines content. An updating of the empirical relationship CRR-KD proposed by Chiaradonna and Monaco (2022) to incorporate the effects of the fines content is currently under development and validation. This paper illustrates the results obtained from application of the new method at the site of San Carlo – Terre del Reno (Ferrara) located in the Emilia-Romagna plain (Italy), where widespread liquefaction occurred in the 2012 seismic sequence. A comprehensive site characterization from previous insitu and laboratory tests carried out by various research groups is available for the sand, silty sand and sandy silt deposits in the San Carlo area. The performance of the new CRR-KD curve accounting for the fines content effect is compared with that obtained by adopting the “clean sand” curves proposed by Chiaradonna and Monaco (2022), as well as with that obtained by using the CPT-based method by Boulanger and Idriss (2014). Even though verified only for specific Italian soils in this area and requiring further field validation, the proposed approach appears as promising to improve the DMTbased liquefaction assessment in silty sands.

Deformability Parameters in the Offshore In-Situ-Test Survey for the New Breakwater Project in Genova Italy

Jesús Sánchez Pinedo — Fri, 07 Jun 2024 13:54:35 +0200

The harbour of Genova is currently protected by a breakwater barrier that is 4 km long. One of the ongoing PNRR projects in Italy consists in dismissing the current breakwater and rebuilding it farther away from shore. The new breakwater will extend to a length of over 6.2 km and allow large cargo and container ships with over 400 m length to access the harbour. The new breakwater will lie in the currently open and unprotected water of the Genova Bay, with water depths up to 50 m. An extensive in situ test campaign of CPT and DMT tests was carried out for soil characterization, to provide stratigraphy, deformability and strength parameters required for the design of the new breakwater foundations. The Manta seafloor penetrometer designed by Geomil was deployed with a crane, operating from a floating pontoon anchored in turn on each of the test locations. The fully automated version of the flat dilatometer (Medusa DMT) and a CPTU tip were alternatively pushed by the Manta, with penetration depths up to over 27 m from seabed. This paper presents results of the moduli obtained from DMT tests employing the standard Marchetti’ formulas and compares them with the interpretation from the CPT using different correlation factors. Additionally, the correlations between Bq (obtained from CPTU) and Ud (obtained from DMT) are analysed.

(S)DMT Tests in Structured Soils. Lessons Learned from Portuguese Granitic Massifs Characterization

Jesús Sánchez Pinedo — Fri, 07 Jun 2024 13:54:19 +0200

Characterization of structured soils by in-situ tests cannot be interpreted with success by applying the methodologies dedicated to sedimentary soils, due to the presence of cemented structures that deeply influences its mechanical behaviour, deviating from Classical Soil Mechanics concepts. From the shear strength point of view, structured soils are represented by two parameters that must be derived simultaneously (cohesion intercept and angle of shearing resistance), which is only possible to achieve in tests that measure more than one parameter, such as DMT, CPTu or PMT tests. In its turn, deformability of structured soils is characterized by 2 yield points, one related with beginning of weak bonds yield (first yield) and another one related with the complete breakage of the bond structure (bond yield or gross yield), which are not present in de-structured soils. As consequence, moduli decay curves are more pronounced than those typically displayed in sedimentary soils. The research based in Portuguese granitic environs tested by (S)DMT has shown its usefulness in the characterization of these structured materials. The whole research frame included the characterization of several sites by means of CPTu and DMT tests, laboratorial testing, a calibration apparatus where DMTs were performed in artificially cemented soils closely controlled by triaxial and other laboratorial tests and several sets of SDMT, PMT, CPTu and triaxial tests performed in a high-quality experimental site (IPG). The accumulated experience arising from these experimental frames will be summarized and discussed in the present paper.

Using Dilatometer to Predict Stress Increase Component of Foundation Settlement

Jesús Sánchez Pinedo — Fri, 07 Jun 2024 13:54:04 +0200

Because soil resists applied stresses in the x, y, and z directions, the ratio of horizontal to vertical stresses, ko, determines the soil stress distribution. The dilatometer test predicts the unit weight of the soil and the horizontal stress ratio at rest, ko, providing the necessary input to determine the stress increase applied to the soil. The Boussinesq stress distribution assumes the soil has a linear elastic stress-strain relationship. This distribution has no input from the soil’s material properties. Harr (1977) proposed using the normal probability distribution with ko input to more accurately compute stress distribution. The authors show the Harr stress distribution for different values of ko and compares them with the Boussinesq stress and Westergaard stress distributions. The authors also present some case studies of stress distribution measurements and proposes modern instrumentation needed for additional research to determine the best prediction method.

Comparative Liquefaction Triggering Assessment of Gravelly Reclamations using the CPT, DPT, and Shear-Wave Velocity

Jesús Sánchez Pinedo — Fri, 07 Jun 2024 13:53:47 +0200

Major challenges are encountered in characterizing and performing liquefaction assessment of gravelly soils since performing traditional in-situ tests, such as the Cone Penetration Test (CPT), in gravelly soils can be challenging, and since gravelly soils are not well-represented in existing case history databases used to develop semi-empirical methods for liquefaction assessment. This has been the primary reason for the ongoing efforts to develop methods based on other invasive tests, such as shear-wave velocity (Vs), and penetration tests with larger probes and greater energy delivered to the rod, such as the Dynamic Cone Penetration Test (DPT). While CPT-based liquefaction analyses have been comprehensively studied, limited research has been conducted comparatively evaluating the performance of the other two methods. This paper performs liquefaction triggering assessment of gravelly reclamations using data from the welldocumented case history of the port of Wellington (New Zealand) using CPT, DPT, and Vs measurements. Results show that while the Vs measurements overestimate liquefaction resistance, the DPT and CPT agreed relatively well with observations from past earthquakes due to the greater sensitivity of these test methods to soil density and stratigraphy

On-site characterization of compacted iron ore tailings-Portland cement blends for dry stacking systems

Jesús Sánchez Pinedo — Fri, 07 Jun 2024 13:50:57 +0200

Dry stacking of filtered tailings has become feasible due to the development of novel dewatering technologies. It offers an alternative to address the safety-related issues associated with conventional slurry disposal in reservoirs confined by upstream heightened dams. The operation and maintenance of such structures are challenging because of the high degree of uncertainty inherent in this material due to its spatial variability in state and gradation. It is also susceptible to liquefaction when saturated and in a loose state. In contrast, the filtered tailings can be compacted and piled up to hundreds of meters to meet prescribed design requirements. Eventually, a cementing agent can be incorporated into the tailings before compaction to enhance the general engineering properties. Nevertheless, few dry-stack facilities operate; none use cement as a stabilising agent. Accordingly, this paper assesses the mechanical response of artificially cemented iron ore tailings compacted in the field to form an experimental pile. Plate load tests and cone penetration tests were used. The experimental pile was divided into four sections, each compacted with different combinations of roller passes (4 or 6 passes) with and without vibration frequency. The results showed that the compacted material was practically insensitive to variations in compaction parameters, as evidenced by similar results in the tested sections' stress-strain responses and cone tip strength values. This study also highlights the effectiveness of field testing in investigating the response of stacking plants and the importance of using a small amount of cement to achieve adequate mechanical performance.

Drying and wetting cycles in tailings dams: effects on physical, mechanical and hydraulic properties

Jesús Sánchez Pinedo — Fri, 07 Jun 2024 13:44:29 +0200

The study examines the drying and wetting cycles of tailings dams (TDs) and their impact on physical, mechanical and hydraulic properties. TDs are divided in four zones: the dike, the discharge zone, the transition zone and the distal zone (also known as the decantation pond). The filling process of the tailings dam involves five phases: 1) dumping and wetting, (2) segregation, (3) sedimentation, (4) consolidation, and (5) drying. The occurrence of drying and wetting cycles depends on the water balance, which can be expressed as Inflow = Outflow ± Storage Coefficient. These cycles are influenced by factors such as changes in the discharge point within TD dike and reservoir, weather conditions, and other external factors. The analysis of drying and wetting cycles in TDs reveals several trends: (a) grain size, density, internal friction angle, and permeability decrease from the discharge zone toward the decantation pond and (b) porosity, fine particle content (particle less than 75 microns), plasticity, cohesion, and capillarity height increase as we move toward the decanting lagoon. Despite these findings, there is currently no established methodology for managing the filling process or controlling wetting and drying cycles of TDs.

Integrated characterisation of bentonite pellet structures for in situ test installation

Jesús Sánchez Pinedo — Fri, 07 Jun 2024 13:43:28 +0200

Bentonite pellet-based mixtures are currently investigated as candidate materials in large-scale in situ sealing experiments such as the Vertical SEALing project by the Institute for Radiological protection and Nuclear Safety (IRSN, France) due to their expected gap-filling capacity in engineered barrier systems for the geological disposal of radioactive waste. In the short term, after installation, the hydro-mechanical behaviour of these pellet-based structures is governed by pellet-pellet interactions, which have been characterised experimentally by oedometer compression tests and numerically by discreteelement modelling of single-layered pellet skeleton samples. In this work, we integrate these experimental and numerical tools to characterise the compressibility of three-layered pellet-based structures with axis-oriented arrangements. We validate the simulated deformation of bentonite pellet samples against experimental data and analyse the evolution of the dry density distribution and axial stiffness along the oedometer compression curve. Our integrated approach has implications for the emplacement and monitoring in situ tests on multi-layered pellet-based barrier systems.

Characterization of residual soil in tailings dam foundations: A combined analysis of in-situ tests and geophysical surveys with emphasis on method correspondence

Jesús Sánchez Pinedo — Fri, 07 Jun 2024 13:43:03 +0200

New legislation in Brazil requires that all upstream tailings dams must be closed. However, understanding the characteristics of the foundation and deposits of these dams can be complex, and conventional investigations may not be sufficient. Geophysical methods can complement conventional approaches and provide a better understanding of geotechnical structures. The objective of this investigation is to comprehensively characterize residual soil from a tailings dam foundation by integrating data from direct and indirect approaches. Data from CPTu, SCPTu, SPT, geophysical profiles, and MASW were analyzed. The results were compared with empirical correlations for other soil types, and it was found that the equations are not effective to represent the materials. The study discusses the advantages and limitations of using these empirical equations.

Development of a 3D ground model to design the stabilisation of a downstream dam founded on weak and liquefiable units

Jesús Sánchez Pinedo — Fri, 07 Jun 2024 13:42:39 +0200

Athree-dimensional (3D) ground model was developed to design the stabilisation of a dam founded on both weak and liquefiable units up to about 18 m below ground surface. The ground model covers a linear extent of approximately 800 m and was developed from five separate site investigations completed over a four-year period and digitisation/georeferencing of historic drawings/plans. Combined, the investigation comprised 206 cone penetration tests (CPTs), 37 boreholes and 36 test pits, including several vane shear tests, ball penetrometer tests and sampling. CPT data was processed to identify different material behaviours, generally based on the following features: corrected tip resistance; sleeve friction resistance; pore water pressure ratio; state parameter; and the soil behaviour type index. Each CPT interpretation was compared with information from the nearest borehole using a purpose-built python code. This information was reviewed manually in an iterative process to delineate the various geotechnical unit based on CPT response and the physical logs. This process identified a continuous weak organic layer across the site which had not been previously picked-up by the Engineer of Record (EoR). The works identified nine separate geotechnical units, with one of these subdividable based on its CPT response/grain size. The 3D ground model was built in Seequent Leapfrog Geo using the following information: unit levels specified from each CPT, digitised historic drawings/plans and a topographic survey. This paper describes the process of development and presents the full 3D ground model used as critical input to the stabilisation design of the dam

Evaluation of the susceptibility to flow liquefaction of an iron ore tailings using the state parameter and Yield Stress Ratio approach

Jesús Sánchez Pinedo — Fri, 07 Jun 2024 13:42:14 +0200

Flow liquefaction is observed in saturated or nearly saturated geomaterials, showing a strain-softening response during undrained shear, primarily in very loose sands and silts, as well as in very sensitive clays. The Cone Penetration Test (CPTu) has been gaining popularity among the geotechnical community to evaluate the state of a soil profile due to its good repeatability, detailed information on the soil stratigraphy and extensive detailed scientific studies to guide the application of the test results. Susceptibility to flow liquefaction is typically evaluated by estimating the in-situ state parameter (ð) since it directly correlates to the soil behaviour at large strain, as shown by Jefferies & Been (2016). Mayne & Sharp (2019) suggested using the yield-stress-ratio (YSR = σp’/σv0’) to estimate the soil state using a threshold of YSR ≈ 3. Currently, in the Brazilian Mining Industry, it is common to find the application of different approaches to evaluating the susceptibility of mining tailings to flow liquefaction (e.g., Plewes et al., 1992; Olson, 2001; Shuttle & Cunning, 2008; Robertson, 2016). This paper presents an evaluation of the susceptibility of an iron ore tailings (IOTs) to flow liquefaction using the following recently published approaches: i) Mayne and Sharp (2019), using the yield stress ratio (YSR) approach; ii) Smith et al. (2021), using a generalised CPTu state parameter inversion method based on the NorSand Widget; and iii) Robertson (2022), with the updated Kc. The main results show a good convergence between the three methodologies used.

Difficulties in Building a Ground Model When Lacking Historic Data Archives and its Impact in TSF Safety Assessment

Jesús Sánchez Pinedo — Fri, 07 Jun 2024 13:41:28 +0200

Sometimes, when working in TSF safety analysis, the historic archives with the original ground topography or details about the TSF design and construction are few or inexistent. The knowledge of the bedrock position, as the details about the embankment construction are essential to know, for instance, the tailings thickness and the construction type. For the analysis of TSF current state stability the ground/structure model is essential, and is, in many cases, very difficult to define with few and low-quality data. The original ground topography is, often, obtained from aerophotogrammetric reconstruction, from satellite images or aerial photos, originally with low resolution and uncertainty of more than 10 m for the elevation. In this paper is presented a case-study from a TSF where the initial data package had only the feasibility design and some very simplified reports that checked the stability of the dam before an upstream raising, i.e. it didn’t exist much information and the details about the site and about the structure were very limited. To “add” difficulties to the process of defining the bedrock surface and to establish the TSF design, the embankments were built with local rocks (mainly schist and phyllite), and during the initial analysis of historical satellite images it was noticed that the original ground was excavated in different areas to increase storage area and obtain construction materials. This paper presents the steps developed to establish the definition of the bedrock ground surface and the difficulties felt and its impacts on TSF safety assessment are discussed.

CPTu for Assessment of Flow Liquefaction of Tailings with Similar Physical Characteristics

Jesús Sánchez Pinedo — Fri, 07 Jun 2024 13:40:28 +0200

A geotechnical assessment of mine tailings state conditions using the static cone penetration test performed at different tailings storage facilities (TSF’s) will be presented in this paper. Both tailings evaluated herein are deposited as a slurry (hydraulic deposition) and have similar grain-size distribution curves. A set of Cone Penetration Tests (CPTu) with pore pressure measurements were performed at each site to evaluate the state of the tailings. To assess the contractive-dilative behavior classical methodologies were adopted such as i) the contractive/dilative boundary suggested by Robertson (2016) ii) the approach suggested by Plewes et al. (1992) and cited by Jefferies and Been (2016) and iii) the yield stress ratio method proposed by Mayne and Sharp (2019). Partial drainage effects will be identified with classical methodologies. The results were compared to evaluate the difference and limitations of each methodology. Comments on the similarity between the two tailings evaluated herein will also be presented to explain the differences in behavior due to aspects such as mineralogy, gradation, stress history and deposition.

Geotechnical Parameters of Filtered Tailings and Waste Rock from the Itabira Complex used in Stacking Projects

Jesús Sánchez Pinedo — Fri, 07 Jun 2024 13:39:31 +0200

The complex where we used the materials ins this study, explores iron ore in an open pit process and is formed by a significant number of mines, and all their geotechnical structures such as waste rock stackings, tailings dams and, recently, the stackings that are being constructed with waste rock and tailings. For the piles formed by the shared disposal of waste rocks and filtered tailings, the characterization of the materials and the strength and critical state parameters determined the executive methodology and the safety factors required for the projects. The waste rocks and filtered tailings are mechanically disposed and divided into zones defined not only according to the geotechnical characteristics of the materials, but also the structural and operational needs of the stacking, which are divided into the confining zone and the confined zone. In the confining zone, compacted waste is deposited. The aim of this procedure is to enhance the structural performance by employing materials with higher resistance. In the confining zone, as closer to the outer layer of the pile, greater shear strength is mobilized. In the confined zone, friable waste, and mining tailings are disposed. In this zone, there is less mobilization of shear strength. For tailings, control and evaluation adhere to parameters outlined by the Critical State Line, employing the void ratio control of layers. This ensures dilatant mechanical behaviours for all confinement stresses specified in the project.

Effects of Vane Size and Aspect Ratio on the Measurement of Undrained Shear Strength of a Fine-Grained Soil

Jesús Sánchez Pinedo — Fri, 07 Jun 2024 13:38:28 +0200

The field Vane Shear Test (VST) is a widely used in-situ test method to measure undrained shear strength and sensitivity of saturated, fine-grained soils. The United States Bureau of Reclamation (Reclamation) commonly performs this test method to help inform numerical modeling of earth embankment dams when undergoing a risk analysis or design. Although the test method itself has been a geotechnical tool for quite some time, its primary use has traditionally been limited to sites with soft and/or relatively shallow clay soil. Typically, embankment and foundation materials of interest at Reclamation facilities are at greater depths, under higher effective stresses, and can be relatively stiff. Testing of stronger soils poses issues when performing the VST; typical commercially available equipment has a limited torque capacity to cause yielding of the soil. As a solution, modifying the dimensions and aspect ratio of the vane is an economic means of increasing the measurable range of undrained strength. Yet, the effects of these modifications are not well understood. Soil strength anisotropy is one of the primary components of this uncertainty. Testing on a sandy lean clay has been conducted to enable side by side comparisons of traditional aspect ratio vanes versus the proposed modified vanes to quantify the potential differences in measured undrained strength. In addition, measured undrained strengths from the various vanes are compared to results of laboratory testing on the same sandy lean clay (i.e., direct simple shear and triaxial compression) to provide a better understanding of the differences between the in-situ and laboratory test methods. This paper presents the apparatus developed to allow full scale vane shear tests to be conducted in the laboratory and summarizes the results of tests on a normally consolidated sandy lean clay.

Analysis of Shear and Consolidation Behaviour of a Clay Foundation Below a Tailings Storage Facility

Jesús Sánchez Pinedo — Fri, 07 Jun 2024 13:37:54 +0200

Historically, the analyses of tailings storage facilities (TSFs) have primarily focused on understanding the characteristics of tailings, while often overlooking a comprehensive evaluation of the foundation, as seen at Mount Polley in 2014. The Global Industry Standard on Tailings Management (GISTM) Requirement 5.4 stresses the importance of comprehensively addressing all potential failure modes. Numerous platinum TSFs in Southern Africa are underlain by residual clay, specifically a residual mafic rock from the Bushveld Complex. Similar soils, known as "tropical black clay soils", are found in other regions of the world. Surprisingly, there's limited public information on testing and modelling the behaviour of this clay foundation. This paper presents a case study that employs a novel approach to assess the impact of loading from tailings deposition on the underlying clay foundation of an upstream TSF. The analysis investigates how shear behaviour and consolidation characteristics of the clay foundation change with varying TSF heights and construction rates. The approach includes quantifying excess pore water pressures and their influence on the clay foundation's effective stress. The analyses primarily employ traditional limit equilibrium methods to assess TSF stability and foundation behaviour, with the potential to expand to numerical modelling. The study concludes that excess pore water pressures will significantly affect the Factor of Safety (FoS) of a TSF, particularly with adverse consolidation characteristics and increasing TSF height. This is primarily due to the low permeability and changing consolidation coefficient (cv) of the clay layer as the surcharge load increases. Furthermore, the research reveals that, depending on the rate of rise, tailings deposition may induce excess pore water pressures, potentially reducing the FoS. The ability to quantify excess pore water pressures using this novel approach enables a more accurate estimation of the FoS for facilities underlain by low-permeability materials, either residual or transported.

Temperature based Leakage Detection and Monitoring Systems in view of Tailings Storage Facilities

Jesús Sánchez Pinedo — Fri, 07 Jun 2024 13:37:36 +0200

Characterizing the in-situ state of soils is essential for evaluating their vulnerability and the consequences of failure. The cone penetration test (CPT) enables efficient, repeatable, and continuous soil characterization based on the recorded response to penetration. Particularly for waste storage facilities, analysis of CPT results can help avoid failures that could lead to significant socio-economic and environmental impacts. Human-made soils in waste storage facilities, like coal combustion products and mine tailings, can have a large fraction of silt-sized particles, which makes them prone to experiencing partial drainage during CPT soundings at standard penetration rates. However, the current state of practice still predominantly adopts the assumption of fully drained or undrained conditions, which may lead to inaccurate interpretation of soil properties and state. This study aims to explore a new CPT-based characterization framework for intermediate silty soils using cone tip resistance values to determine the soil state. To do so, CPT soundings were performed in-flight in centrifuge models of a coal combustion product with different initial densities at varying penetration velocities. Soils with a low density and contractive behavior experience a decrease in tip resistance as the penetration velocity is increased due to the generation of excess pore pressures, resulting in high ratios of drained to undrained tip resistance (Qtn,drained/Qtn,undrained). In contrast, the tip resistance increases with penetration velocity, resulting in low Qtn,drained/Qtn,undrained ratios in soils of a high density and dilative behavior. The proposed framework uses Qtn,drained/Qtn,undrained to identify contractive layers and is expected to help assess the vulnerability of soil layers to experience liquefaction failure.

Characterization of coal combustion products using variable rate CPT in a geotechnical centrifuge

Jesús Sánchez Pinedo — Fri, 07 Jun 2024 13:37:19 +0200

Cone penetration test assessment to identify fluid-like tailings to support a tailings storage facility deconstruction

Jesús Sánchez Pinedo — Fri, 07 Jun 2024 13:37:01 +0200

This paper presents the implementation of a Cone Penetration Test (CPT)-based methodology to identify fluid-like tailings in the Tailings Storage Facility (TSF) pond to support a TSF deconstruction. The TSF discussed in this paper was partially raised upstream and classified as very high risk due to its location, next to a creek and a short distance to the downstream community. The owner's preferred mitigation strategy was to proceed with the TSF deconstruction. To inform the deconstruction planning, a comprehensive geotechnical site investigation was conducted, which included CPTu and boreholes with continuous thin wall tube sampling from a floating platform. The investigation identified tailings in the pond as high plasticity clays (CH) with a geotechnical fines content exceeding 95 %. The CPT results indicated low tip resistance, nearly linear pore pressure measurements, and minimal sleeve friction, suggesting the presence of fluid-like tailings in a significant portion of the TSF. The implementation of this methodology allowed to systematically confirm the presence of fluid-like tailings across the pond and define their extent. This information supported the owner’s decision to employ mechanical excavation taking advantage of the tailings flowability. The observations made during the tailings excavation confirmed a good agreement between the CPT assessment and the actual material behaviour. These findings underscore the efficacy of the CPT-based method in guiding safe TSF deconstruction projects

Evaluating the dynamic liquefaction potential of tailings: a comparison of simplified methods

Jesús Sánchez Pinedo — Fri, 07 Jun 2024 13:36:42 +0200

The state of the practice to evaluate the dynamic liquefaction potential of a soil column entails the use of simplified methods that compares the cyclic stress ratio with the cyclic resistance ratio. One of the most used methods is the Boulanger & Idriss 2014, which relies on cone penetration test data to estimate in-situ cyclic resistance ratio and cyclic stress ratio distributions, considering corrections factors for soils with fine contents. Saye, Olson and Franke in 2021 presented a novel method to assess liquefaction susceptibility using cone penetration test data on soils ranging from non-sensitive clays to clean sands. The procedure was developed using +400 documented case records of liquefaction and non-liquefaction in clean sands, silty sands, sandy silts, and low plasticity fine grained soils. Although promising, this method is not widely used in the industry yet. This paper presents a comparison between both methods for tailings. It uses cone penetration test soundings performed in tailings with a wide range of mineralogy and fine contents, combined with variations in peak ground accelerations and magnitudes. This analysis shows that Saye, Olson and Franke’s method is generally more robust, particularly for the analysis of fine tailings, as Boulanger & Idriss’ method relies on site specific data or the engineer’s judgement to define an Ic cut-off value that screens out clay-like soils from the liquefaction analysis.

Correlation Between Shear Wave Velocity From Borehole Seismic and CPT Data for the Application of Numerical Analysis

Jesús Sánchez Pinedo — Fri, 07 Jun 2024 13:31:28 +0200

The Federal Waterways and Shipping Administration of Germany is currently planning the construction of a lock next to the existing Lueneburg twin ship lift on the Elbe Lateral Canal. The vertical lift of both the ship lift and the new lock is 38 m. The lock will be the biggest of its kind worldwide and will require an excavation pit of about 260 m length, 60 m width and 26 m depth. The adjacent ship lift is a major constraining factor for the project, as it must remain in operation throughout construction and thereafter. As part of an extensive site investigation, geophysical crosshole measurements were carried out up to a depth of 70 m to obtain dynamic soil properties necessary for the numerical analyses. This paper shows the results of the geophysical survey as well as a comparison of the in-situ measurements with well-established CPT correlations. The comparison shows a moderate to good match for the dynamic soil parameters such as the smallstrain shear modulus Gmax or the shear wave velocity Vs respectively, providing confidence in the derived soil parameters across the site.

Probabilistic soil model for seismic risk assessment based on SDMT results

Jesús Sánchez Pinedo — Fri, 07 Jun 2024 13:30:30 +0200

A new geotechnical site investigation has been conducted in the southern breakwater basin of the Port of Barcelona, for which hundreds of in-situ and lab tests have been performed. Among these tests, this study focuses on the evaluation of triple points. That is, at the prospected locations, there are results from seismic dilatometer Marchetti test (SDMT), cone penetration tests (CPTu), and laboratory tests based on soil samples. Based on this information, the probabilistic distribution of the dynamic and geometrical properties of the soil profiles can be properly characterized. Eleven closely spaced boreholes have been used to characterise the statistical properties of the input variables. The objective of this article is twofold. First, the probabilistic generation of one-thousand soil profiles, which are statistically compatible with the data provided by the eleven aforementioned boreholes. Secondly, to analyse how the elastic properties of the generated soil profiles evolve once seismic waves have passed through them. To do so, a large set of ground motion recorded in hard soils have been employed. Results show that the dynamic response of the soil can be properly parametrized if considering intensity measures extracted from the ground motions acting at the bedrock level. From the results obtained, fragility functions have been derived for risk assessment purposes.