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The French National Radioactive Waste Management Agency is leading the design of a deep geological radioactive waste disposal to be located in the Callovo-Oxfordian formation. At the disposal main level, large-diameter galleries will ensure access to the storage cells and connection between zones. After a long operational period, the disposal will be closed by sealing structures located at some key positions to ensure post-closure safety over the long term. The seals are intended to prevent the flow of water and the migration of radionuclides from the disposal to the biosphere throughout the entire storage life. Thus, the long-term safety of the disposal relies to a large extent on the performance of these structures. The paper presents the work carried out to assess and simulate the phenomena underlying the response and performance of a large-diameter sealing concept under real disposal conditions. The complexity of the problem is addressed by considering in the simulations large-scale 3D geometries, advanced constitutive models, complex coupled phenomena, key geometric details at decimetre scale, and all the phases from the excavation to the post-closure period (~¿a few thousand years)., Peer Reviewed, Postprint (published version)

Soil layering modifies cone penetration measurements when the cone is close to layer boundaries. Transition zone and thin-layer effects appear, complicating interpretation. To help identify the mechanisms underlying transition and thin-layer effects, several series of realistic simulations of cone penetration in layered soils are presented. Cone penetration tests are simulated using fully coupled hydromechanical models solved with the particle finite element method. A constitutive model capable of representing flow liquefaction is employed to explore the effect of embedded layers with different initial state parameter and/or hydraulic conductivity than the host soil. Sensing and development distances for tip resistance and excess pore pressure are examined, as well as the effect of layering on dissipation tests. It is shown how distortion of layer interfaces by the cone is captured, explaining several characteristics of pore pressure and dissipation records. It is also shown that looser soil states may be hidden in the tip resistance trace by simultaneous changes in soil hydraulic conductivity., Financial support of Spain Research Agency (MCIN/AEI/10.13039/501100011033) through the Severo Ochoa Centre of Excellence project (CEX2018- 000797-S) and research project PID2020-119598RB- I00., Peer Reviewed, Postprint (author's final draft)

This study focuses on the modelling of a gas injection experiment to assess the effects of incorporating heterogeneous material properties. The numerical model considers a two-phase flow coupled hydro-mechanical problem, and includes embedded fractures that open with deformation, thereby enhancing permeability. The approach used is integrated in the CODE_BRIGHT software, which allows for the consideration of geomaterials with a spatially correlated heterogeneous field of porosity that follows a normal distribution. This spatial correlation can be either isotropic or anisotropic. A key aspect of this approach is that material properties such as intrinsic permeability, diffusivity or cohesion are defined as a function of porosity. Consequently, these properties also exhibit heterogeneity with spatial correlation and, eventually, anisotropy. The results derived from the numerical model align well with in-situ measurements. The study also includes sensitivity analyses to the variation of critical variables. The calibration of the model has been validated through a similar experiment. The findings indicate that the consideration of heterogeneous material properties can have a significant influence on gas injection problems, particularly when a hydraulic fracture is formed., This research was supported by ANDRA through the DECOVALEX Project and by the CODE_BRIGHT Project (CIMNE, International Centre for Numerical Methods in Engineering). The second author was supported by a CSC scholarship (No. 202008390058)., Peer Reviewed, Postprint (published version)

This keynote lecture discusses the results of a long lasting experimental research, devoted to the investigation of clay microstructure and its evolution upon loading. Micro-scale analyses, involving scanning electron microscopy, image processing, mercury intrusion porosimetry and swelling paths to test the clay bonding, are presented on clays subjected to different loading paths, with the purpose of providing experimental evidence of the processes at the micro-scale which underlie the clay response at the macro-scale. Data from the literature on clays of different classes, either soft or stiff, are compared to original results on two stiff clays, Pappadai and Lucera clay, both in their natural state and after reconstitution in the laboratory. The results presented herein allow building a conceptual model of the evolution of clay microstructure upon different loading paths, providing microstructural insights into the macro-behaviour described by constitutive laws and advising their mathematical formalization in the framework of either continuum mechanics or micro-mechanics. For editorial purposes, the research results are presented in two parts. The first part, presented in this paper, concerns the results for reconstituted clays, whereas a second part, concerning the corresponding natural clays, is discussed in a second companion paper., Peer Reviewed, Postprint (published version)

The paper describes the development of a high-pressure isotropic cell for studying the environmental degradation of low porosity clayey rocks. Air permeability measurements are used in this device as a tool to evaluate rock degradation in unsaturated rock specimens caused by mechanical, hydraulic and chemical paths. A modified equation, based on the air pressure decay method proposed by Yoshimi and Osterberg (1963), is presented. The proposed method is applied to an Australian clayey shale. Estimated values of air permeability are compared against those calculated using the original method which, in the case of low porosity rocks, seems to provide unrealistic values when the air pressure in the vessel decays beyond 50%., Postprint (published version)

This paper presents the results of the initial molding of the large-scale gas injection test 1 (Lasgit) conducted at the Äspö Hard Rock Laboratory in Sweden. Lasgit is a field test that follows the Swedish KBS-3V disposal concept, in which copper/steel canisters containing spent nuclear fuel are deposited in disposal boreholes drilled into the repository tunnels' floor. Bentonite blocks are used to fill the space around each canister, which will eventually swell and seal any gaps. Once hydrated, the bentonite acts as a diffusional barrier to prevent the migration of radionuclides. The gas flow process is influenced significantly by material heterogeneity and local deformability, and material properties are not constant throughout. The initial medium structure is non-uniform, and deformations can result in changes in hydraulic properties and structure. Therefore, material heterogeneity is critical in the THM modeling process. To simulate the tests, a coupled hydro-gas-mechanical 3D numerical model was developed. The model assumes initial permeability to be heterogeneous and includes embedded fractures in the formulation. The model accurately reproduces the observed gas pressure evolution during the test., Postprint (published version)

The mechanical response of natural soils is characterized by a narrow elastic domain, a smooth transition between elastic to elasto-plastic regime, and hysteretic behaviour during cyclic loading. These realistic features can be efficiently intro-duced into an existing constitutive model by reformulating it in the framework of subloading surface plasticity. This unconven-tional elasto-plastic approach is advantageous over other techniques, since it allows to retain some stress history information only by adding an additional constitutive parameter and one hardening rule. In this paper, CASM, a state parameter dependent, critical state model, is reformulated in the framework of subloading plasticity. Several element tests are reported to illustrate the performance of the model., Postprint (published version)

The paper presents the enhancement of an existing constitutive model for argillaceous hard soils-weak rocks to incorporate non-isothermal conditions to be used in coupled thermo-hydro-mechanical (THM) simulations of underground excavations subjected to temperature variations within the context of deep geological nuclear waste disposal. The proposed thermo-elastoplastic extension accounts for the effect of temperature on the yield and plastic potential functions and on the elastic stiffness. The resulting model is validated through the simulation of relevant non-isothermal laboratory tests reported in the literature. The model is then applied to the coupled THM simulation of an in situ heating test conducted at the Meuse/Haute-Marne underground research laboratory in Bure, France, excavated in the Callovo-Oxfordian claystone. Results show that the incorporation of thermal effects into the constitutive description of the host rock plays a significant role in the behaviour of the excavation when subjected to thermal loading, particularly in the evolution of the excavation fractured zone., Peer Reviewed, Postprint (author's final draft)

This paper presents a new interpretation procedure to estimate the initial state parameter from cone penetration testing (CPTu) in undrained conditions based on the results from a comprehensive set of numerical simulations of CPTu in low permeability liquefiable soil. CPTu simulations are performed using the Particle Finite Element Method, whereas the material response is modelled with the Clay and Sand Model. The effects of soil constitutive parameters and roughness of the soil–steel interface are examined. It turns out that the numerical results are correctly summarized by an analytical relation derived from undrained cavity expansion results in critical state soils, as long as the constraints resulting from cone geometry are taken into account. The resulting adapted analytical formulation is notable for its simplicity and ease of use, comparing favorably with existing alternatives., The authors wish to thank Dr. Stefano Collico (UPC), Mr. Davide Besenzon (Escuela Superior Politécnica del Litoral) and Mohammad Razavinasab (CIMNE) for fruitful discussions at the beginning of the research. Financial support of Ministerio de Ciencia e Innovación of Spain (MCIN/AEI/10.13039/501100011033) through the Severo Ochoa Centre of Excellence project (CEX2018-000797-S) and research project PID2020-119598RB-I00 is gratefully appreciated., Peer Reviewed, Postprint (author's final draft)

En el context de les obres d'enginyeria civil que involucren sòls, es destaca la importància d'utilitzar mètodes de càlcul específics adaptats a les característiques del terreny. En aquest sentit, s'aborda el cas de la construcció d'un nou edifici al moll Adossat del dic de l'Est, situat al Port de Barcelona, on sorgeixen interrogants a causa de la presència de sòls tous normalment consolidats, altament compressibles i de baixa permeabilitat al terreny natural. Prèviament a la construcció, es van realitzar dos estudis d'estabilitat utilitzant el programa PLAXIS, que es basa en el mètode dels elements finits i permet analitzar el comportament dels sòls mitjançant diferents models de comportament del sòl. No obstant això, les mesures d'auscultació realitzades al moll van revelar assentaments a llarg termini al terreny natural que superaven significativament els assentaments calculats pel model utilitzat en l'estudi de l'estructura. Aquests assentaments addicionals s'atribueixen a un fenomen conegut com a consolidació secundària del sòl, que s’havien tingut en compte inicialment en la simulació de projecte. Per abordar aquesta problemàtica, es proposa desenvolupar un model numèric utilitzant el programa PLAXIS que representi de manera precisa el comportament del terreny natural mitjançant la incorporació d’un model específic per la consolidació secundaria. En primer lloc, es realitzarà una anàlisi d'estabilitat, examinant la influència de la consolidació secundària en el factor de seguretat de la construcció. Posteriorment, s'analitzaran detalladament els assentaments generats pel model i s'ajustarà adequadament el coeficient de consolidació secundaria perquè els assentaments predits s'aproximin el màxim possible als valors mesurats a les auscultacions. Els resultats obtinguts a partir d'aquesta anàlisi seran discutits i analitzats., En el contexto de las obras de ingeniería civil que involucran suelos, se destaca la importancia de utilizar métodos de cálculo específicos adaptados a las características del terreno. En este sentido, se aborda el caso de la construcción de un nuevo edificio en el muelle Adosado del dique del Este, ubicado en el Puerto de Barcelona, donde surgen interrogantes debido a la presencia de suelos blandos normalmente consolidados, altamente compresibles y de baja permeabilidad en el terreno natural. Previo a la construcción, se realizaron dos estudios de estabilidad utilizando el programa PLAXIS, que se basa en el método de los elementos finitos y permite analizar el comportamiento de los suelos mediante diferentes modelos de comportamiento del suelo. Sin embargo, las mediciones de auscultación que se llevaron a cabo en el muelle revelaron asentamientos a largo plazo en el terreno natural que superaron significativamente los calculados por el modelo utilizado en el estudio de la estructura. Estos desplazamientos adicionales se atribuyen a un fenómeno conocido como consolidación secundaria del suelo el cual no se había considerado inicialmente en la simulación del proyecto. Para abordar esta problemática, se propone desarrollar un modelo numérico utilizando el programa PLAXIS que represente de manera precisa el comportamiento del terreno natural mediante la incorporación de un modelo específico para la consolidación secundaria. Primero, se llevará a cabo un análisis de estabilidad, donde se examinará la influencia de la consolidación secundaria en el factor de seguridad de la construcción. Después, se analizarán detalladamente los asentamientos generados por el modelo y se ajustará adecuadamente el coeficiente de consolidación secundaria con el fin de que los desplazamientos predichos se aproximen lo más posible a los valores medidos en las auscultaciones. Los resultados obtenidos a partir de este análisis serán discutidos y analizados., In the context of civil engineering works involving soils, the importance of using specific calculation methods adapted to the characteristics of the terrain is highlighted. In this regard, the case of the construction of a new building on the Adosado dock of the Eastern breakwater, located in the Port of Barcelona, is addressed, where questions arise due to the presence of normally consolidated, highly compressible, and low permeability soft soils in the natural ground. Prior to the construction, two stability studies were conducted using the PLAXIS program, which is based on the finite element method and allows analysing the behaviour of soils using different soil behaviour models. However, the monitoring measurements carried out on the dock revealed long-term settlements in the natural ground that significantly exceeded those calculated by the model used in the structural study. These additional displacements are attributed to a phenomenon known as secondary consolidation of the soil, which was not initially considered in the project simulation. To address this issue, it is proposed to develop a numerical model using the PLAXIS program that accurately represents the behaviour of the natural ground by incorporating a specific model for secondary consolidation. First, a stability analysis will be carried out, examining the influence of secondary consolidation on the safety factor of the construction. Then, the settlements generated by the model will be carefully analysed, and the coefficient of secondary consolidation will be properly adjusted to make the predicted displacements approximate the values measured in the monitoring. The results obtained from this analysis will be discussed and analysed.

Bentonite barriers are a key component in may designs of deep geological repositories for high level nuclear waste. During the hydration stage, the bentonite undergoes non-uniform changes in dry density that may persist even after reaching a fully saturated state. Since dry density controls the properties of the bentonite that ensure the functions of safety of the barrier, the potential of bentonite for homogenization or otherwise is a matter of high relevance. The paper presents the results and the analyses of two hydration tests on initially heterogenous samples, especially designed to explore the phenomena and processes underlying the homogenisation of bentonite materials. The formulation and constitutive model used in the analyses are briefly presented followed by a description of the tests. Subsequently, the experimental dataobtained from the tests are discussed together with the results of the hydromechanical analyses performed. Particular attention is given to the degree of homogenization of the specimens achieved at the end of the tests. The simulations have resulted in a very satisfactory agreement with test observations, especially egarding the final state of the samples, thus enhancing the confidence in the numerical tool employed., The work presented has been developed in the framework of the Bentonite Mechanical Evolution Project (BEACON). The project receives funding from the Euratom research and training programme 2014-2018 under grant agreement No 745942. The support of Conacyt (Id. no. 710153) to the third author is also gratefully acknowledged., Postprint (published version)

A northbound motorway close to the city of Barcelona has shown various deformation signs in its pavement and, as a consequence, it has been the subject of numerous studies and projects, aimed at reducing the road maintenance costs. In the area object of the present study, the road follows a slope, which is located below an old quarry converted in a waste disposal facility before the deformation signs appeared in the motorway. An extensive instrumentation system was installed along the slope adjacent to the motorway. The available monitoring data has allowed to identify the instability of the slope as the cause of the deformation signs in the motorway, as well as to locate the failure surface in various sections of the slope. The paper describes the analysis of the evolution of the instability phenomenon and presents the stabilizing measure adopted. The reduction of the observed slope movement rate shows the success of the stabilizing measure., Postprint (published version)

Node-based smoothed finite element (NS-FEM) formulations for the coupled hydro-mechanical problem are now becoming popular in soil mechanics, but there has been limited comparative study of their performance. In this work, a node-based formulation is developed for the coupled hydro-mechanical problem (u-pw formulation) using low-order, equal-order interpolants and an implicit time marching scheme for the global problem. The numerical properties of the resulting formulation are then compared to different implementations of classical finite elements. The use of nodal smoothing does not render by itself the solution stable at the undrained limit, on the contrary, the range of undrained instability is increased. Stabilizing terms previously employed in FEM are equally successful in stabilizing NS-FEM solutions, but the computational cost of the stabilized solution is much higher for NS-FEM. It is also shown that NS-FEM does not present by itself any particular advantage in terms of mesh dependency over classic FEM: when strain localization is present the solution obtained is strongly dependent on mesh size., Financial support of Ministerio de Ciencia e Innovación of Spain (MCIN/AEI/10.13039/501100011033) through the Severo Ochoa Centre of Excellence project (CEX2018-000797-S) and research project PID2020-119598RB-I00 is gratefully appreciated., Peer Reviewed, Postprint (author's final draft)

A controlled re-saturation of a heated 50 cm long column made of MX-80 bentonite pellets in the CIEMAT laboratory facilities (Madrid, Spain) has been running for 10 years (2011-2021). The experimental data on the saturation state and the swelling response of the bentonite material at high temperatures provided useful information for the verification of a double-porosity approach that considers the hydro-mechanical coupling between the micro- and macro-pore levels and the definition of retention curves for each structural domain. The numerical modelling with this double-porosity model has shown to be able to reproduce the main behaviour features observed in the lab test., Postprint (published version)

This paper presents the results of a centrifuge study in which swell of an expansive clay profile was induced in the centrifuge. A factor which has previously hindered such research is the time required to induce significant swell in-flight, within a reasonable time frame. In this study the use of an artificially fissured fabric together with geotextile layers allowed for a significant magnitude of swell to be achieved within a matter of hours. Measurements of matric suction and water content throughout testing highlight the potential difficulties associated with such measurements in a fissured profile. The suction in clay along the interfaces of fissures can be significantly reduced almost instantaneously with the ingress of water. In contrast, elements closer to the centre of intact masses may take significantly longer to respond, illustrating the role of the dual processes (and hence dual scaling laws) of moisture ingress along fissures, followed by diffusion associated with swelling of the clay. A comparison of the magnitude of swell induced in this centrifuge model with that of conventional oedometer swell tests indicated gross overpredictions from the oedometer testing. In this comparison, the severe limitation of oedometer tests reducing a sample to a point of zero suction is emphasised. Finally, it is illustrated how an understanding of the rate of swell throughout an expansive profile can provide insights into the validity of the predictions from oedometer swell tests., The authors gratefully acknowledge the financial support from the UK Engineering and Physical Sciences Research Council (EPSRC) under the Global Challenges Research Fund for the project “Developing performance-based design for foundation systems of WIND turbines in AFRICA (WindAfrica)”, Grant Ref: EP/P029434/1. The authors also thank Rick Vandoorne and Paul le Roux for reviewing this paper and providing valuable feedback., Peer Reviewed, Postprint (published version)

Este proyecto de fin de máster tiene como objetivo garantizar la estabilidad de un talud proponiendo una técnica de estabilización. En el caso de estudio del presente trabajo, se descargó material de la cabeza del talud para revertir el fenómeno de inestabilidad., This master thesis project has the objective to guarantee the stability of a slope by proposing a stabilization technique. In the case study of the present work, the head of the slope was unloaded to reverse the instability phenomenon.

Two case histories involving harbour works in a deltaic environment are described in the paper. The mechanisms underlying delta formation and development are outlined first; they involve climate changes, geological processes and human effects. The history of the Llobregat delta, the location of the case histories, is presented. The first case concerns the design and construction of a vertical caisson breakwater. The incorporation of storm wave loading, the description of the geological setting and the bases for stability evaluation are discussed. Special attention is given to the stability of the structure during the construction period when stability issues are more critical. The use of the envisaged observational method was hampered by the limited monitoring data available resulting in a modification of the planned approach. The second case refers to the reconstruction of the Prat quay after a major failure caused by the flow liquefaction of the hydraulically-deposited backfill. Post-failure investigation and analyses identified the need for reducing the liquefaction potential of the backfill and enhancing the undrained shear strength of the foundation clay; preloading was the main ground improvement method selected. The observational method was used to steer the construction activities to ensure an adequate margin of safety. The paper closes with some general considerations of the role of geology, observational method and judgement in the cases reported., Postprint (published version)

En el laboratorio subterráneo de Meuse-Haute Marne (Francia), se han desarrollado extensas investigaciones para examinar el efecto de la excavación de túneles en una roca arcillosa: la argilita del Callovian-Oxfordian. Se ha prestado especial atención a la generación de una zona dañada alrededor de la excavación. El hecho de que la roca tenga una resistencia relativa-mente limitada implica que esta zona dañada pueda alcanzar una extensión significativa. Se ha demostrado que el daño en la roca se manifiesta en una serie de fracturas de tensión y de corte en la zona cercana al túnel. Una observación importante es que la configuración de la zona dañada y las deformaciones que se producen como consecuencia de la excavación dependen considera-blemente del estado inicial de las tensiones in situ. La anisotropía en el comportamiento mecánico de la roca también ejerce una influencia notable. En el presente trabajo se presenta una modelización numérica de la generación de la zona dañada por la exca-vación del túnel. La modelización tiene características especiales que son clave para poder reproducir la localización de defor-maciones y la generación de fracturas: el uso de un modelo constitutivo que tiene en cuenta las características básicas de este ti-po de rocas y la incorporación de una formulación no local para poder abordar de forma consistente problemas que involucran materiales cuasi-frágiles y reblandecibles. Se demuestra que el modelo resultante es capaz de reproducir satisfactoriamente las observaciones de campo., Postprint (published version)

Disturbance of specimens recovered by tube sampling from boreholes is an enduring relevant problem in geotechnical engineering. Practice has evolved slowly in this area, partly because the main research method applied, involving comparative field sampling and testing, remains strictly empirical. Theoretical approaches based on the strain path method (SPM) have been applied, that idealize the problem as one of steady ideal fluid motion, which is an unrealistic premise. A novel numerical technology, the Particle Finite Element method, is here applied to simulate smooth tube sampling using a conventional elasto-plastic Tresca model for the undrained soil. The results obtained are used to quantify the qualitative insight gained by field experimentation. It is shown that sample straining is proportional to the tube area ratio. The coefficient of proportionality is named here as the Hvorslev fraction. It is shown that the Hvorslev fraction is dependent on end-tube bevel and on the presence of a stationary piston. Furthermore, it is also shown that the contribution of these two features is independent of one another. The approach described represents an advance towards a soil mechanics-based rational approach to soil sampling., This work has been supported by the Ministry of Science and Innovation of Spain through research grant BIA2017-84752-R. The authors acknowledge financial support from the Spanish Ministry of Economy and Competitiveness, through the ‘Severo Ochoa Program for Centers of Excellence in R&D’ (CEX2018-000797-S)., Postprint (published version)

En Enero de 2019 en Brumadinho (Brasil) una presa de relaves mineros de gran tamaño colapsó en su totalidad de forma brusca, causando la muerte a 270 personas y una gran conmoción en la minería mundial. La rotura fue capturada en video por una cámara que permitió identificar rápidamente el modo de rotura como uno de licuación. La cuestión pendiente era saber cómo se había desencadenado la licuación en este caso, pues los desencadenantes más habituales de este fenómeno como el sis-mo, la lluvia o las actividades de construcción brillaban por su ausencia. En este artículo se presentan brevemente los ensayos y análisis numéricos que se han llevado a cabo para responder tal pregunta en el marco de una investigación encargada por la Fis-calía (Ministerio Público Federal) de Brasil., Postprint (published version)

Failures due to static liquefaction have been too frequent in tailings dams. Stress-deformation numerical analyses based on critical state theory are able to reproduce those failures and may be used to gain insight into the different factors involved. One factor that is sometimes believed to play a role in liquefaction triggering is tailings creep, i.e. rate effects intrinsic to the tailings material. These timedependent effects are here explored using a constitutive viscoplastic model, referred to as CASMvisco. Effects on viscous parameters, stress level, and raising history on undrained creep are explored using simulated triaxial compression tests. The effect of creep-enabled consolidation is illustrated by the numerical simulation of a dam failure triggered by slope erosion., Postprint (published version)

Entre los años 2006 y 2018, una autovía de titularidad autonómica situada al norte de la ciudad de Barcelona ha presentado diversas patologías asociadas tanto a su firme como a la ladera que la rodea. El movimiento de la zona objeto de estudio se ha auscultado mediante un extenso sistema de monitorización que ha permitido identificar la inestabilidad de la ladera como la causa de las patologías de la autovía. Con la finalidad de reducir la velocidad del movimiento observado y aumentar el factor de seguridad del talud, se decidió realizar la descarga de la cabeza del mismo. La actuación llevada a cabo está siendo beneficiosa, relativamente rápida y de coste limitado. La evolución del movimiento observado en función de la descarga pone de manifiesto la eficacia de la medida adoptada., Los autores desean expresar su agradecimiento a Infraestructuras de la Generalitat de Catalunya, S.A.U. por el apoyo dado a la elaboración del presente trabajo. Se agradece también la ayuda CEX2018-000797-S relativa a los centros de excelencia “Severo Ochoa” (2019-2023) financiada por MCIN/AEI/10.13039/501100011033., Postprint (published version)

North of the city of Barcelona, a slope adjacent to a road has been showing signs of instability for a few years. In the area object of the present study, the road borders an existing river and its pavement has shown damage as a consequence of the slowing moving slope. The road, in operation since the ‘90s, has heavy traffic levels, hence its good performance and safety is an absolute priority for the local Administration. The paper describes a new database facility, specifically designed to control and monitor the unstable slope with the aim of guaranteeing the quality as well as the safety of the infrastructure. In order to analyse the slope instability phenomenon and to obtain accurate information on its evolution, an extensive system of topographical and geotechnical instrumentation was installed in 2017, allowing the determination of the location of the slip surface in various sections of the slope. The numerous monitoring data are gathered in a new database facility, which allows a real-time visual connection to the site and also stores ground investigation data, activities records, technical reports as well as other relevant information about the slope. The database, which has a GIS interface, can be used in the future to access data from other sites to display, compare and analyse information from different projects., Postprint (published version)

La construcción de una estación de metro en Barcelona requirió la ejecución de una excavación profunda en un área densamente urbanizada. Las condiciones geológicas de la obra eran complicadas por la presencia de materiales aluviales blandos bajo el nivel freático. Debido a esta complejidad, la caracterización del terreno basada en pruebas de laboratorio resultaba muy difícil. Los ensayos in situ y en especial los ensayos dilatométricos ofrecieron una alternativa válida para estimar el comportamiento tensodeformacional de los materiales y, en especial, su rigidez en el rango de las pequeñas deformaciones. Un amplio sistema de instrumentación permitió auscultar los movimientos inducidos por la excavación. Los datos de monitorización se utilizaron para validar análisis numéricos de elementos finitos con el objetivo de realizar previsiones de clase A para algunas fases del proceso constructivo. Las previsiones numéricas y los datos de auscultación muestran en general un buen acuerdo. La excavación se ha llevado a cabo con éxito., Los autores desean expresar su profundo agra-decimiento a Infraestructures de la Generalitat de Catalunya, S.A.U. por el apoyo dado en la elaboración del presente trabajo. Ayuda CEX2018 – 000797 - S financiada por MCIN/AEI/10.13039/501100011033., Postprint (published version)

Al norte de la ciudad de Barcelona, un talud adyacente a una carretera presenta signos de inestabilidad desde hace unos años. Un extenso sistema de instrumentación topográfica y geotécnica ha permitido observar el movimiento del talud y localizar la superficie de deslizamiento en diversas secciones del mismo. Los numerosos datos de auscultación se han analizado en su conjunto con la finalidad de seguir la evolución del movimiento y entender sus causas. Para estudiar el fenómeno de inestabilidad y obtener información sobre su posible evolución, se han realizado análisis numéricos que han permitido, entre otras cosas, seleccionar medidas de estabilización eficaces para la ladera. En el presente trabajo, se describen los detalles del estudio numérico y se comparan los resultados con las observaciones in situ., Los autores desean expresar su agradecimiento a Infraestructuras de la Generalitat de Catalunya, S.A.U. por el apoyo dado a la elaboración del presente trabajo. Se agradece también la ayuda CEX2018-000797-S relativa a los centros de excelencia “Severo Ochoa” (2019-2023) financiada por MCIN/AEI/10.13039/501100011033., Postprint (published version)

The mechanical properties of a high plasticity expansive clay from South Africa are reported. The experimental programme considered wetting after loading tests followed by one-dimensional consolidation and unloading of undisturbed and statically compacted samples. The results of this study illustrate that laboratory preparation of expansive clays do little to alter the soil's swell characteristics. This finding is attributed to the fact that, due to numerous swelling and shrinking cycles over a geological time frame, expansive clays tend to have reworked fabric in-situ. The effects of structure are also assessed in both undisturbed and compacted specimens by comparison of the various consolidation tests with that of a reconstituted sample. The results illustrate a gradual yielding process for both undisturbed and compacted specimens, indicating progressive disruption of structure. After consolidation, while the expansion indices were found to be similar for both compacted and undisturbed samples, measured values were lower than that of the reconstituted specimen. Such a result is indicative of some preservation of structure after testing. It is also emphasised that consolidation tests on expansive clays are likely to exist in structure permitted space if swelling strains are restricted during the inundation process. Conversely, for most results presented it is seen that the swell caused by the inundation phase is approximately as disruptive to structure as laboratory preparation and compaction., The authors also thank Dr Gerrit Smit of the University of Pretoria for his valuable insights throughout this study. This work was funded by the UK Engineering and Physical Sciences Research Council (EPSRC) under the Global Challenges Fund programme for a project entitled ‘Developing Performance based design for foundations of wind turbines in Africa (WindAfrica)’, Grant Ref: EP/P029434/1. The first author would also like to acknowledge the Newton Fund UnsatPractice PhD exchange programme (grant Ref: ES/N013905/1), which enabled him to spend six months at Durham University during his PhD study at the University of Pretoria.v, Peer Reviewed, Postprint (published version)

The paper presents the work carried out to assess and simulate numerically the phenomenology behind the response of large diameter intermediate-level long-lived nuclear waste (ILW-LL) storage galleries and the corresponding sealing structures. Large scale models were created for this purpose, using advanced constitutive models, accounting for complex coupled phenomena, and representing geometric details at decimeter scale. These challenging simulations provided qualitative and quantitative results on key questions related to the design of this kind of structures, such as the extension of the damaged zone around the gallery, the impact of the thermal load on the water pressure variation around the excavation and on the surrounding geological layers, the duration of the natural hydration phase and the swelling pressure development of the sealing core, and the seals system global stability., Postprint (published version)

A sensitivity study is presented to evaluate the influence of different parameters on the simulation of an underground excavation in the Callovo-Oxfordian (COx) argillaceous formation performed in the Meuse/Haute-Marne underground research laboratory. An elasto-viscoplastic constitutive law representing the characteristic behaviour of indurated mudrocks and stiff clays has been employed. It incorporates anisotropy, strain-softening, creep deformations and dependence of permeability on damage. In addition, a non-local formulation, able to simulate localised deformations objectively, has been incorporated in the analyses. The following features affecting the excavation have been studied: initial stress, strength and stiffness anisotropy, strength parameters, hydraulic and hydromechanical parameters, and scale effects. A simulation reported in a companion paper provides the base case for benchmarking. The results are compared in terms of extent and configuration of the excavation fractured zone, vertical and horizontal tunnel convergences, and the development and evolution of pore pressures in the rock. From the comparisons, an enhanced understanding of the hydromechanical mechanisms associated with underground excavations in COx claystone, and other similar argillaceous materials, has been achieved., We are grateful for the financial and technical assistance of the French national radioactive waste management agency (Andra) to the work presented. The technical assistance of Plaxis is also gratefully acknowledged. The first author has been supported by a Conacyt scholarship (Reg. No. 270190)., Peer Reviewed, Postprint (author's final draft)

The paper presents the numerical simulation of an underground excavation in the Callovo-Oxfordian argillaceous formation, performed in the Meuse/Haute-Marne underground research laboratory, within the context of deep geological nuclear waste disposal. The constitutive model adopted incorporates a number of characteristic features of the hydromechanical behaviour of the Callovo-Oxfordian claystone, and other indurated clays, including anisotropy and time-dependent deformations. Model parameters have been largely determined from available experimental results. Particular attention has been given to the incorporation of a non-local formulation in order to simulate localised deformations objectively. It is shown that the numerical analysis is able to provide a very satisfactory reproduction of the extent and configuration of the excavation-induced fractured zone, the development of rock displacements and the evolution of water pressures in the rock. The analysis is also able to provide a deeper insight into the mechanisms underlying the generation of water pressures inside the rock mass., Peer Reviewed, Postprint (author's final draft)

The use of stress–deformation analyses to evaluate the characteristics of possible static liquefaction events is rapidly becoming the norm for tailings dams exposed to such risk. Ideally, those analyses should be based on constitutive models that incorporate the fundamental mechanics of the problem, are able to perform robustly in commercial numerical platforms and are simple to calibrate. A model that aims to fulfil that specification is proposed. The model is a new implementation of a previously proposed model based on critical state concepts that is able to represent static liquefaction. The model formulation is elaborated to show that all the required inputs can be related to familiar concepts such as the critical state line, the state parameter, the normalised undrained peak strength or the coefficient of earth pressure at rest. The methodology is illustrated by analysing the failure of the Merriespruit tailings dam, which occurred in South Africa in 1994 and was instrumental in the recognition of how widespread liquefaction risk might be in saturated tailings. Numerical analysis of the case showed how a large static liquefaction failure might have been triggered by a relatively small slope erosion caused by overtopping., Peer Reviewed, Postprint (author's final draft)

Borehole tube sampling is a key process of geotechnical engineering. The paper presents numerical analyses of smooth tube sampling in clay using the Particle Finite Element Method (PFEM). The soil is described by a conventional elasto-plastic constitutive model (Tresca plasticity and a quasi-incompressible elastic law). The sampler is advanced by several diameters into the soil until a steady state is observed. The elasto-plastic numerical solution for a round-tipped sampler clearly identifies a localized shear failure mechanism at the entrance of the tube. Relevant Strain Path Method (SPM) solutions are numerically evaluated to facilitate full field comparison. For a given thickness ratio elasto-plastic simulation predicts far less compression but much larger extensions at the centerline than SPM. The results also show how including a beveled sampler tip or a stationary piston changes the failure mechanism and significantly reduces induced peak extension strains. The results agree with available experimental data and well-established empirical observations. The methodology presented may open the way to a soil mechanics based rational approach to soil sampling simulation., This work has been supported by the Ministry of Science and Innovation of Spain through research grant BIA2017-84752-R. The third author acknowledge financial support from the Spanish Ministry of Economy and Competitiveness, through the "Severo Ochoa Programme for Centres of Excellence in R&D" (CEX2018-000797-S), Peer Reviewed, Postprint (author's final draft)

An investigation of clay microstructure and its evolution under 1D and isotropic compression is presented for different clays. Data from the literature are compared to original results on two Italian clays, obtained using SEM, image processing, MIP and on-purpose swelling tests. The effects of composition and loading history on clay microstructure, as well as its changes along the compression path (pre- and post-gross-yielding) are analysed and a conceptual model of microstructure evolution is proposed for the clays under study. NC clays at early virgin compression, either natural or reconstituted, are found to possess an open fabric of random-low orientation, complying with a prevailing inter-aggregate and a smaller intra-aggregate porosity, whose size and distribution depend on composition. Under 1D compression, either in the field or in the laboratory, the inter-aggregate porosity is lost, at a rate dependent on composition and loading history, and the dominant intra-aggregate micro-pore is progressively reduced. Accordingly, perfectly oriented stacks of domains are recognised which, though, embed preserved random particle arrangements even at large pressures, resulting in an increase of average orientation up to the reach of a steady orientation degree. Isotropic compression causes faster microstructure evolution, although large pressures are required to change 1D-induced fabric orientation., Peer Reviewed, Postprint (author's final draft)

From the combination of existing modelling approaches, a constitutive framework is presented for the numerical modelling of soft structured clays. The formulation accounts, in a natural way, for time-dependent phenomena such as stress relaxation, loading rate dependency, ageing, and creep deformations under constant load. It also incorporates the effect of soil structure and its degradation under mechanical loading. To demonstrate the potential of the proposed approach, a constitutive model is presented, based on this framework, and it is applied to the simulation of a number of laboratory tests from the literature., Postprint (published version)

Scott Sloan (1954–2019) was a leader of academic engineering in Australia and beyond, as evidenced by his numerous professional accolades and important research achievements, which have had significant impact on his chosen profession of geotechnical engineering. Educated in Australia and the United Kingdom, he returned to Australia in 1984 and developed a large and active research group at the University of Newcastle, and tackled a wide range of important problems in civil and mining engineering. These include the development of computational methods to predict the mechanical behaviour of soil and rock masses, and his pioneering methods to predict the collapse states of structures made of, on, and in, earth materials, allowing engineers to design cheaper and safer civil infrastructure around the globe. Sloan established long-standing international collaborations and was awarded many honours for his research achievements. He was also a keen and skilful fisherman and a more than competent blues guitar player., Postprint (published version)

Static liquefaction of soils that have a brittle undrained response (hydraulic fills, mine tailings or sensitive clays) may lead to sudden failures of large consequence. Given the importance of undrained failure, obtaining precise estimates of peak and residual yield strength is important. The CPTu plays a major role in the geotechnical characterization of these geomaterials and so do CPTu-based estimates of undrained strength. Most of the methods available for CPTu-based estimation of undrained strength are empirical, based on correlation with other laboratory or field tests. When such correlations are established difficulties appear due to variable disturbance affecting the reference laboratory samples and parasitic effects, such as unaccounted for partial drainage during penetration or unknown side friction, affecting the cone results. Such difficulties are not present when using numerical simulation. The paper builds upon a series of CPTu simulations using a model able to represent brittle undrained failure. Confounding factors such as partial drainage and cone side friction are systematically varied to examine their effect on the results. The results are then employed to examine the performance of several empirical methods frequently employed to obtain peak and residual strength from CPTu., The authors acknowledge financial support from the Spanish Ministry of Economy and Competitiveness, through the “Severo Ochoa Programme for Centres of Excellence in R&D” (CEX2018-000797-S)., Postprint (published version)

Both static and dynamic penetration tests are widely used to conduct soil investigation practice. Particle crushability has been known to greatly affect the responses of penetration tests. On the other hand, the physical property of granular materials – surface roughness – exhibits considerable influence on crushability. The virtual calibration chamber (VCC) technique, based on the Discrete Element Method (DEM), is used to investigate the effect of particle crushability and roughness on both static and dynamic penetration test responses. In static tests particle crushing reduces tip resistance, and roughness enhances this effect as rough particles crush more than smooth ones. The main effects of roughness and crushability on dynamic responses lie in the track of dynamic penetrograms. The analysis confirms a good correlation between an equivalent dynamic resistance and the static tip resistance., This work has been supported by the Ministry of Science and Innovation of Spain through research grant BIA2017-84752-R. The authors acknowledge financial support from the Spanish Ministry of Economy and Competitiveness, through the ‘Severo Ochoa Program for Centers of Excellence in R&D’ (CEX2018-000797-S)., Postprint (published version)

The possibilities of the particle finite element method (PFEM) for modeling geotechnical problems are increasingly evident. PFEM is a numerical approach to solve large displacement and large strain continuum problems that are beyond the capabilities of classical finite element method (FEM). In PFEM, the computational domain is reconfigured for optimal solution by frequent remeshing and boundary updating. PFEM inherits many concepts, such as a Lagrangian description of continuum, from classic geomechanical FEM. This familiarity with more popular numerical methods facilitates learning and application. This work focuses on G-PFEM, a code specifically developed for the use of PFEM in geotechnical problems. The article has two purposes. The first is to give the reader an overview of the capabilities and main features of the current version of the G-PFEM and the second is to illustrate some of the newer developments of the code. G-PFEM can solve coupled hydro-mechanical static and dynamic problems involving the interaction of solid and/or deformable bodies. Realistic constitutive models for geomaterials are available, including features, such as structure and destructuration, which result in brittle response. The solutions are robust, solidly underpinned by numerical technology including mixed-field formulations, robust and mesh-independent integration of elastoplastic constitutive models and a rigorous and flexible treatment of contact interactions. The novel features presented in this work include the contact domain technique, a natural way to capture contact interactions and impose contact constraints between different continuum bodies, as well as a new simplified formulation for dynamic impact problems. The code performance is showcased by the simulation of several soil-structure interaction problems selected to highlight the novel code features: a rigid footing insertion in soft rock, pipeline insertion and subsequent lateral displacement on over-consolidated clay, s, The authors acknowledge financial support by Severo Ochoa Centre of Excellence (2019–2023) Grant No. CEX2018-000797-S funded by MCIN/AEI/10.13039/501100011033 and research projects BIA2017-84752-R and PID2020-119598RB-I00., Peer Reviewed, Postprint (published version)

Con el objetivo de aumentar el conocimiento acerca de los suelos blandos deltaicos del puerto de Barcelona para futuras actuaciones portuarias, se ha realizado una extensa campaña de investigación geotécnica en un área de aproximadamente 2500 x 220 m con calados comprendidos entre 8 y 20 m. Los trabajos de campo se llevaron a cabo desde dos plataformas tipo jack-up con patas de hasta 45 m de longitud, trabajando simultáneamente 24 horas durante cerca de 8 meses. Los trabajos com-prendieron la ejecución de 85 sondeos a rotación con recuperación de testigo, incluyendo 508 SPT y 412 muestras inalteradas ti-po Shelby, 103 CPTU con ensayos de disipación, y 11 ensayos DMT cada 0.5 m, así como una extensa campaña de ensayos de laboratorio. La profundidad media de investigación fue de 40 m. Este artículo presenta los resultados de dicha investigación, centrados en 8 puntos triples, compuestos por DMT, CPTU y sondeo con recuperación de testigo y muestras inalteradas. Se ha comparado la densidad del suelo y algunos parámetros resistentes estimados a partir de correlaciones bien conocidas de DMT y CPTU con los resultados de laboratorio en muestras inalteradas. Además, se han comparado los parámetros básicos de ambos ensayos in-situ a partir de las ecuaciones existentes. Finalmente, se han evaluado las correlaciones empleadas para el caso de los suelos blandos del delta del Llobregat y se han analizado sus incertidumbres., Postprint (published version)

Penetration depth of Spudcan foundations for offshore mobile Jack-up rigs is typically predicted by considering a wished-in-place foundation at different depths and following traditional bearing capacity approaches. However, the large penetration depths involved, stress redistributions and the flow of the material around the spudcan are some example of features which make the wished-in-place assumption quite unrealistic. This paper presents an open access application package developed to simulate and hence predict load penetration curves of spudcan installation in multi-layered clay profiles. The numerical tool adopts the recently developed particle finite element method for geotechnical applications (G-PFEM). The potential of this large strain particle finite element application is demonstrated by simulating field data from the literature. The results show that load-penetration curves obtained using G-PFEM capture more efficiently the field results with respect to other numerical and analytical methods. It is also shown how the G-PFEM automatically captures cavity infill. In the paper the computational cost for the simulation of penetration up to 40m on a standard desktop are shown to be low compared to other commercial software., This work has been supported by the Ministry of Science and Innovation of Spain through research grant BIA2017-84752-R. The authors acknowledge financial support from the Spanish Ministry of Economy and Competitiveness, through the ‘Severo Ochoa Program for Centers of Excellence in R&D’ (CEX2018-000797-S)., Postprint (published version)

The geo-science and engineering fields have critical roles to play towards a sustainable energy future. This state-of-the-art review focusses on five areas where the geotechnical community has been involved the most: the oil and gas sector with emphasis on methane hydrates, carbon geological storage, geothermal, energy geo-storage, and nuclear waste storage. Extensive tables in the appendix identify potential geotechnical contributions to all energy resources (mining is critically needed to supply raw materials for the energy sector, yet is not addressed in this review). Energy-related applications involve a wide range of time and length scales, coupled thermo-hydro-chemo-mechanical processes, multi-phase fluids, high pressure-temperature-stress conditions, fines migration, reactive fluid transport and phase transformations, and multi-physics repetitive loads. Analysis and design require careful experimentation (including field-scale studies) and advanced numerical simulations. Educational programs must address the knowledge needs in energy geo-engineering., Postprint (published version)

A series of gas injection tests on Callovo-Oxfordian (COx) claystone from the Bure underground research laboratory (URL) in France were carried out at the British Geological Survey (BGS). The tests were performed using a triaxial apparatus specifically designed to capture small volumetric strains induced by the injected gas flow and consequent material dilatancy. The long-duration experiments were monitored throughout. Measurements also included pressure, stresses (axial and radial stresses prescribed for each test stage), rate of gas inflow, gas outflow volume as well as pore-pressures observed at various points of the sample. A coupled hydro-gas-mechanical 3D numerical model has been developed to simulate the tests. Initial permeability is assumed heterogeneous throughout the specimen and embedded fractures are incorporated in the formulation. Gas pressure-induced deformations during the test lead to variations of permeability due to changes in matrix porosity and, especially, fracture aperture as well as fracture orientation due to material anisotropy. A programme of sensitivity analyses involving the variation of different aspects and parameters of the model contributes to a better understanding of the phenomena and highlights its complexity. The model is able to reproduce the observed behaviour of the tests., DECOVALEX is an international research project comprising participants from industry, government and academia, focusing on development of understanding, models and codes in complex coupled problems in sub-surface geological and engineering applications; DECOVALEX-2019 is the current phase of the project. The authors appreciate and thank Andra for funding this work, as well as all DECOVALEX-2019 Funding Organizations Andra, BGR/UFZ, CNSC, US DOE, ENSI, JAEA, IRSN, KAERI, NWMO, RWM, SÚRAO, SSM and Taipower for their financial and technical support of the work described in this report. The authors wish to acknowledge Elena Tamayo-Mas, Jon Harrington, Jean Talandier, Gilles Armand and Alex Bond for their constructive comments and discussions during the modelling work carried out in the context of DECOVALEX-2019, as well as the reviewers of the manuscript during the submission process of this study, which allowed to substantially improve the paper in a clear way. The authors wish also to acknowledge the support of the International Centre for Numerical Methods in Engineering (CIMNE) and the funding received from the Spanish Ministry of Economy and Competitiveness through the “Severo Ochoa Programme for Centres of Excellence in R&D” (CEX2018-000797-S). The statements made in the report are, however, solely those of the authors and do not necessarily reflect those of the Funding Organizations., Peer Reviewed, Postprint (published version)

This study focuses on the thermo-hydro-mechanical (THM) analysis of the behaviour of a full-scale engineered barriers experiment designed to study the long-term response of a disposal concept for high-level radioactive waste (HLW) and spent fuel (SF). Crucially, the test involved two dismantling operations, a partial one after 5 years of heating and a final one, after 18·3 years of operation, allowing the direct observation of the state of the barrier at two different times. The coupled THM modelling discussed in this paper mainly focuses on the last 13 years of test operation and also on the final dismantling of the barrier system. The numerical model was unchanged from the early stages of the test, so the results presented can be considered as blind predictions. The numerical model predicted reasonably well the state of the barrier and its evolution, especially in terms of the distribution of the bentonite dry density, confirming the predictive capability of the model to capture the transient THM processes. The combination of experimental and numerical investigations, involving one of the most long-lasting full-scale in situ experiments monitoring the behaviour of the barrier components of an HLW/SF repository, has led to a better understanding of the THM behaviour of this complex system., Peer Reviewed, Postprint (author's final draft)

In this work, the suitability of several meshing strategies to optimize the CPU time consumption is investigated. The mesh sensitivity strategy is established by applying the basic framework of a coupled hydro-gas-mechanical 3D FEM numerical model to simulate the tests in terms of types of the elements, number of elements and nodes to quantify the influence of different meshes on the accuracy of the test results with regard to optimization of the CPU time consumption. In this study, the problem is represented and the performance and calculation time of both element types and mesh size in the utilized 3D FEM model are checked. To achieve this, both tetrahedral and hexahedral meshes and their refinement/coarsening are generated. Then the performance of the element types and sizes on the test results are compared. This is a main issue for modelling gas injection through clay-based engineered isolation barriers that requires clear up-scaled tests due to full-scale experiments., Postprint (published version)