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  • Multi-scale analysis of cone penetration test (CPT) in a virtual calibration chamber

     Butlanska, Joanna; Arroyo Alvarez de Toledo, Marcos; Gens Sole, Antonio; O'Sullivan, Catherine
    Canadian geotechnical journal
    Date of publication: 2014-01
    Journal article

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

  • Abrasivity measures on geotechnical materials of the Barcelona area

     Gonzalez Gonzalez, Juan Carlos; Arroyo Alvarez de Toledo, Marcos; Gens Sole, Antonio
    ISRM European Rock Mechanics Symposium
    Presentation's date: 2014-05-26
    Presentation of work at congresses

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    Cutting tool replacement and maintenance operations might take up to a quarter of the total active time on mechanized tunnel excavation. Tool wear estimation is therefore necessary for accurate planning and costing of such operations. One of the main factors affecting tool replacement rates is abrasivity. Abrasivity is a property of geomaterials that quantifies their ability to cause wear on the tools interacting with them. There are several index tests (e.g. CAI) that are in use to quantify abrasivity. However, most of them are inappropriate when the tunnel operation passes through soils and rocks. In this communication we present a methodology applied to obtain a uniform measure of abrasivity for all the geotechnical units encountered on 23 km of tunnels recently perforated in the Barcelona area with different EPBs machines. The geotechnical conditions encountered were very heterogeneous, ranging from soft soils to hard and medium rocks, and frequently resulting in mixed soil-rock conditions. LCPC-type abrasivity measurements were obtained in all the materials.A descriptive summary of the main trends revealed by the data is presented. The ability of this test to evaluate abrasivity in all circumstances is highlighted by comparison with the more limited results achieved when applying other measurement methods

  • A chemo-mechanical constitutive model accounting for cation exchange in expansive clays

     Guimarães, Leonardo do N; Gens Sole, Antonio; Sánchez, M.; Olivella Pastalle, Sebastian
    Géotechnique
    Date of publication: 2013-03-01
    Journal article

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  • Homogenization in clay barriers and seals: two case studies

     Gens Sole, Antonio; Vállejan, Beatriz; Zandarín Iragorre, Maria Teresa; Sánchez, M.
    Journal of rock mechanics and geotechnical engineering
    Date of publication: 2013-06
    Journal article

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    The paper presents two case studies that provide information on the process of homogenization of initially heterogeneous clay barriers and seals. The first case is the canister retrieval test performed in the Aspö Hard Rock Laboratory (Sweden). The heterogeneity arises from the use of a combination of blocks and pellets to construct the engineered barrier. The degree of homogenization achieved by the end of the tests is evaluated from data obtained during the dismantling of the test. To assist in the interpretation of the test, a fully coupled thermo-hydro-mechanical (THM) analysis has been carried out. The second case involves the shaft sealing test performed in the HADES underground research laboratory (URL) in Mol (Belgium). Here the seal is made up of a heterogeneous mixture of bentonite pellets and bentonite powders. In addition to the full scale test, the process of homogenization of the mixture has also been observed in the laboratory using X-ray tomography. Both field test and laboratory tests are successfully modelled by a coupled hydro-mechanical (HM) analysis using a double structure constitutive law. The paper concludes with some considerations on the capability of highly expansive materials to provide a significant degree of homogenization upon hydration.

  • Steady state of solid-grain interfaces during simulated CPT

     Butlanska, Joanna; Arroyo Alvarez de Toledo, Marcos; Gens Sole, Antonio
    Studia Geotechnica et Mechanica
    Date of publication: 2013
    Journal article

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

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

  • The Buen Pastor Cathedral in San Sebastián

     Gens Sole, Antonio; Alonso Pérez de Agreda, Eduardo; Jubany Casanovas, Jorge; Uzcanga, Luis
    Date of publication: 2013
    Book chapter

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    The construction of an underground car park required an excavation in sand under the water table adjacent to the cathedral of Buen Pastor in San Sebastián, Spain. Because of the close proximity of the cathedral and other buildings, control of ground movements was a paramount consideration in the design. Construction involved the use of diaphragm walls propped by the floor slabs using the top-down technique. A monitoring system was installed to control the performance of the excavation throughout. For water control during the excavation, the diaphragm walls reached an underlying low permeability silt layer. This decision required the adoption of special measures to connect hydraulically the foundation ground of the cathedral with the water levels prevailing in the outside area. Excavation was completed with very limited ground movements that caused no observable damage in the cathedral and other nearby structures. Piezometer records also proved that the installed hydraulic connection performed satisfactorily.

  • Coupled thermo-hydraulic pulse tests on two reference Belgian clay formations

     Lima Amorim, Analice França; Romero Morales, Enrique Edgar; Gens Sole, Antonio; Vaunat, Jean; Li, X.L.
    International Symposium on Coupled Phenomena in Environmental Geotechnics
    Presentation's date: 2013-07
    Presentation of work at congresses

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    Boom and Ypresian clays are being studied in Belgium in connection with the design of a repository for radioactive waste. Within this context, thermal impact may play an important role on the behaviour of these low-permeability clays. To evaluate this impact, heating pulse tests on intact borehole samples were carried out using an axi-symmetric and constant volume heating cell with controlled hydraulic boundary conditions. Attention is focused on the time evolution of temperature and pore water pressure changes along heating and cooling paths -i.e., pore pressure build-up during quasi-undrained heating and later dissipation to the applied hydraulic boundary conditions. A coupled thermo-hydro-mechanical finite element program was used in a first stage to determine thermal parameters by back-analysis and then to simulate selected experimental results on Boom clay

    Boom and Ypresian clays are being studied in Belgium in connection with the design of a repository for radioactive waste. Within this context, thermal impact may play an important role on the behaviour of these low-permeability clays. To evaluate this impact, heating pulse tests on intact borehole samples were carried out using an axi-symmetric and constant volume heating cell with controlled hydraulic boundary conditions. Attention is focused on the time evolution of temperature and pore water pressure changes along heating and cooling paths -i.e., pore pressure build-up during quasi-undrained heating and later dissipation to the applied hydraulic boundary conditions. A coupled thermo-hydro-mechanical finite element program was used in a first stage to determine thermal parameters by back-analysis and then to simulate selected experimental results on Boom clay

  • Ventilation effects in an argillaceous rock tunnel examined via unsaturated soil mechanics

     Gens Sole, Antonio; Garitte, Benoit
    Pan-American Conference on Unsaturated Soils
    Presentation's date: 2013-02
    Presentation of work at congresses

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    The paper presents the observations, analysis and interpretation of a long-term ventilation test performed in the Mont Terri underground laboratory. An unlined 1.3 m diameter tunnel excavated in Opalinus clay has been subjected to two controlled ventilation periods. Extensive instrumentation has provided observations concerning relative humidity, pore pressures and displacements in the rock. In addition, boreholes have been drilled at several times during the experiment to obtain independent measurements of water content and degree of saturation of the rock. It has been found that an unsaturated zone surrounding the tunnel, though small in extent, largely controls the progress of drying and other effects associated with ventilation. The interpretation of the test has been based on a coupled multi-phase hydromechanical numerical model in which unsaturated soil mechanics concepts such as vapour diffusion, relative permeability and retention curve play a paramount role. 2013 Taylor Francis Group, London.

  • Sensitivity to damping in sand production DEM-CFD coupled simulations

     Climent Pera, Natalia; Arroyo Alvarez de Toledo, Marcos; O'Sullivan, Catherine; Gens Sole, Antonio
    International Conference on Micromechanics of Granular Media
    Presentation's date: 2013
    Presentation of work at congresses

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    A three dimensional numerical model based on Discrete Element Method (DEM) and coupled with Computational Fluid Dynamics (CFD) was implemented to simulate sand production. Simulations with no fluid flow conditions and with fluid flow conditions have been performed and the sensitivity of the simulations to numerical damping is studied.

    A three dimensional numerical model based on Discrete Element Method (DEM) and coupled with Computational Fluid Dynamics (CFD) was implemented to simulate sand production. Simulations with no fluid flow conditions and with fluid flow conditions have been performed and the sensitivity of the simulations to numerical damping is studied.

  • Stiff clays and mudstones: fundamentals, progressive failure and deep underground excavations

     Gens Sole, Antonio
    Darmstädter Geotechnik-Kolloquium: Jubiläumskolloquium
    Presentation's date: 2013-03
    Presentation of work at congresses

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    The subject of this contribution is the hydromechanical behaviour of stiff clays and mudstones, i.e. geological materials in which fine grained particles predominate. It is especially focussed on argillaceous materials that are intermediate between soils and rocks not only with respect to strength but also in terms of porosity and compressibility. Because of space limitations, only sorne salient aspects of the behaviour are outlined herein. First, sorne general aspects of the mechanical behaviour are high1ighted, afterwards the issues of brittleness and progressive failure are addressed and finally sorne observations of their hydromechanical response in underground excavations are presented.

  • Abrasividad y su influencia en el rendimiento de una excavación mecanizada

     González Paez, Claudia; Arroyo Alvarez de Toledo, Marcos; Gens Sole, Antonio
    Obras y proyectos. Revista de ingeniería civil
    Date of publication: 2013
    Journal article

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

  • Analysis of hydro-mechanical processes in a ventilated tunnel in an argillaceous rock on the basis of different modelling approaches

     Garitte, Benoit; Bond, A.; Millard, A.; Zhang, C.; Mcdermott, C.; Nakama, S.; Gens Sole, Antonio
    Journal of rock mechanics and geotechnical engineering
    Date of publication: 2013-02
    Journal article

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

  • Anisotropy effects in a deep excavation in stiff clay

     Vaunat, Jean; Gens Sole, Antonio; Barboza De Vasconcelos, Ramon
    International Conference on Computational Plasticity Fundamentals and Applications
    Presentation's date: 2013-09
    Presentation of work at congresses

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    This paper tackles the issues related to the excavation of a horizontal gallery carried out in Boom clay, a tertiary clay that hosts the Underground Laboratory of the Belgium Nuclear Agency (SCK-CEN). The gallery is 85 m long, 5 m wide and connects one of the laboratory access shafts to a horizontal drift drilled from the second access shaft. Displacement and pore water pressure sensors installed from both gallery ends allowed for a detailed monitoring of the hydro-mechanical response of the clay rock before, during and after gallery excavation. A striking feature of the response concerns the strong changes measured in pore water pressure at distances as large as 60m from the excavation front. To explore and discriminate the mechanisms controlling such pore pressure changes, 2D axisymmetric Finite Element hydro-mechanical calculations have been carried out. An elastoplastic constitutive law based on Mohr-Coulomb criterion has been considered for the material. Several types of analyses have been performed: a) material and stress state are isotropic; b) material is isotropic but stress state is orthotropic and, c) material and stress state are orthotropic. Results allow for explaining the field measurements and identifying the key variables that control the clay response around the drift.

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    Triaxial tests on frozen ground: formulation and modelling  Open access

     Casini, Francesca; Gens Sole, Antonio; Olivella Pastalle, Sebastian; Viggiani, Giulia M.B.
    International Conference on Computational Plasticity Fundamentals and Applications
    Presentation's date: 2013-09
    Presentation of work at congresses

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    Artificial Ground Freezing (AGF) is a controllable process that can be used by engineers to stabilise temporarily the ground, provide structural support and/or exclude groundwater from an excavation until construction of the final lining provides permanent stability and water tightness. In this work, the process of ground freezing is studied using a constitutive model that encompasses frozen and unfrozen behaviour within a unified effective-stress- based framework and employs a combination of ice pressure, liquid water pressure and total stress as state variables. The parameters of the constitutive model are calibrated against experimental data obtained from samples retrieved during construction of Napoli underground, in which AGF was extensively used to excavate in granular soils and weak fractured rock below the ground water table.

    Artificial Ground Freezing (AGF) is a controllable process that can be used by engineers to stabilise temporarily the ground, provide structural support and/or exclude groundwater from an excavation until construction of the final lining provides permanent stability and water tightness. In this work, the process of ground freezing is studied using a constitutive model that encompasses frozen and unfrozen behaviour within a unified effective-stress- based framework and employs a combination of ice pressure, liquid water pressure and total stress as state variables. The parameters of the constitutive model are calibrated against experimental data obtained from samples retrieved during construction of Napoli underground, in which AGF was extensively used to excavate in granular soils and weak fractured rock below the ground water table.

  • Coupled thermo-hydro-mechanical analyses for freezing soils

     Gens Sole, Antonio; Nishimura, S.; Casini, F.; Olivella Pastalle, Sebastian; Jardine, R.
    International Conference on Computational Methods for Coupled Problems in Science and Engineering
    Presentation's date: 2013-06
    Presentation of work at congresses

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

  • Soil movements associated with compensation grouting during line 9 excavation in Barcelona: a case study

     Di Mariano, Alessandra; Gens Sole, Antonio; Mair, Robert
    International Conference Computational Methods in Tunneling and Subsurface Engineering
    Presentation's date: 2013-04
    Presentation of work at congresses

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    The paper describes a case history -related to the Line 9 excavation in Barcelonawhere compensation grouting was initially proposed to minimize the movements of the buildings close to or directly above the tunnel alignment, some of which have piled foundations. Unexpectedly, the ground settlements due to the pre-conditioning stage of the compensation grouting became very significant leading to some light damage to one of the buildings. Eventually, the decision was taken to stop the treatment. Grouting-induced displacements are compared to the movements produced by tunnelling that were very limited. The paper concludes with some considerations concerning the suitability of ground treatment in the context of carefully-executed tunnelling operations.

  • Coupled THM analysis of a nuclear waste repository in crystalline rock

     Sanchez, Marcelo Dolores; Dontha, L; Gens Sole, Antonio; Guimarães, Leonardo do N
    US Rock Mechanics / Geomechanics Symposium
    Presentation's date: 2013-06
    Presentation of work at congresses

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    This paper presents the Thermo-Hydro-Mechanical (THM) analysis of an isolation system for high level nuclear waste. A geological disposal facility of such type encompasses both: natural (host rock) and engineered barriers (generally clay based). The study deals on an ongoing large scale heating test at full scale that is being carried at the Grimsel test site under actual conditions. The experiment reproduces the conditions of a HLW repository, at full scale under actual conditions. Key thermohydro-mechanical (THM) variables such as temperature, relative humidity, stresses and fluid pressures were measured in the clay barrier and surrounding rock. The test is intensely instrumented and has provided the opportunity to study in detail the evolution of the main THM variables over a long period of time. A comprehensive laboratory investigation was carried out in the context of the FEBEX and NF-PRO European projects has allowed the identification of the model parameters to describe the THM behavior of the compacted clay and the sub-rounding rock. This paper focuses mainly on the numerical analysis of the main THM variables in the granite adjacent to the repository. Overall, the comparisons between model predictions and observations are quite satisfactory.

    This paper presents the Thermo-Hydro-Mechanical (THM) analysis of an isolation system for high level nuclear waste. A geological disposal facility of such type encompasses both: natural (host rock) and engineered barriers (generally clay based). The study deals on an ongoing large scale heating test at full scale that is being carried at the Grimsel test site under actual conditions. The experiment reproduces the conditions of a HLW repository, at full scale under actual conditions. Key thermohydro-mechanical (THM) variables such as temperature, relative humidity, stresses and fluid pressures were measured in the clay barrier and surrounding rock. The test is intensely instrumented and has provided the opportunity to study in detail the evolution of the main THM variables over a long period of time. A comprehensive laboratory investigation was carried out in the context of the FEBEX and NF-PRO European projects has allowed the identification of the model parameters to describe the THM behavior of the compacted clay and the sub-rounding rock. This paper focuses mainly on the numerical analysis of the main THM variables in the granite adjacent to the repository. Overall, the comparisons between model predictions and observations are quite satisfactory.

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    Elastoplastic modelling of a foundation on an unsaturated soil  Open access

     Gonzalez, Nubia Aurora; Gens Sole, Antonio
    International Conference on Computational Plasticity Fundamentals and Applications
    Presentation's date: 2013-09
    Presentation of work at congresses

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    This paper presents a coupled flow-deformation finite element analysis of a shallow foundation on an unsaturated loosely compacted silt subjected to variations in the water level. The behaviour of the silt foundation was simulated using the Barcelona Basic Model (BBM) which was implemented into the PLAXIS finite element code. Material parameters were calibrated from laboratory tests reported in the literature. The influence of partial soil saturation and of fluctuations of the groundwater level on the behaviour of footing is investigated.

    This paper presents a coupled flow-deformation finite element analysis of a shallow foundation on an unsaturated loosely compacted silt subjected to variations in the water level. The behaviour of the silt foundation was simulated using the Barcelona Basic Model (BBM) which was implemented into the PLAXIS finite element code. Material parameters were calibrated from laboratory tests reported in the literature. The influence of partial soil saturation and of fluctuations of the groundwater level on the behaviour of footing is investigated.

  • A simplified procedure to assess the dynamic stability of a caisson breakwater

     Madrid, R.; Gens Sole, Antonio; Alonso Pérez de Agreda, Eduardo; Tarrago, Dani
    International Conference on Soil Mechanics and Geotechnical Engineering
    Presentation's date: 2013-09
    Presentation of work at congresses

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    The paper describes a simplified method of analysis used to evaluate the stability of a caisson breakwater to sea wave actions. An intensive laboratory program was performed in order to evaluate the static and dynamic characteristics of the foundation soil. Anisotropic and isotropic consolidated cyclic triaxial tests and cyclic simple shear tests were used to define the cyclic interaction diagram for the foundation soil. The possibility of foundation cyclic mobility due to wave loading and their effect on the breakwater stability was examined combining the cyclic interaction diagram with the results of finite element analysis. The potential reduction in soil strength is then incorporated into a conventional stability analysis. The procedure is illustrated by a specific application to a caisson breakwater that is part of the extension works of the Barcelona Harbour.

    The paper describes a simplified method of analysis used to evaluate the stability of a caisson breakwater to sea wave actions. An intensive laboratory program was performed in order to evaluate the static and dynamic characteristics of the foundation soil. Anisotropic and isotropic consolidated cyclic triaxial tests and cyclic simple shear tests were used to define the cyclic interaction diagram for the foundation soil. The possibility of foundation cyclic mobility due to wave loading and their effect on the breakwater stability was examined combining the cyclic interaction diagram with the results of finite element analysis. The potential reduction in soil strength is then incorporated into a conventional stability analysis. The procedure is illustrated by a specific application to a caisson breakwater that is part of the extension works of the Barcelona Harbour.

  • Development of a predictive framework for geothermal and geotechnical responses in cold regions experiencing climate change

     Nishimura, S.; Jardine, R.; Fenton, C.H.; Olivella Pastalle, Sebastian; Gens Sole, Antonio; Martin, C.J.
    International Conference on Soil Mechanics and Geotechnical Engineering
    Presentation's date: 2013-09
    Presentation of work at congresses

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    Cold regions, which are expected to suffer particularly severe future climate effects, will pose very challenging geotechnical conditions in the 21st century involving ground freezing and thawing. Given the uncertainty of future environmental changes and the vast expanses of the cold regions, it is appropriate to address problems such as pipeline or road construction with analytical methods that have multiple scales and layers. High- and middle-level predictive tools are described that integrate climatic predictions from AOGCMs and their down-scaling schemes, geological and topographical (DEM) information, remotely-sensed vegetation data and non-linear finite element analysis for soil freezing and thawing. These tools output broad scale predictions of geothermal responses, at a regional scale, that offer hazard zoning schemes related to permafrost thawing. A more intensive localscale predictive tool is then outlined that considers fully-coupled thermo-hydro-mechanical processes occurring at the soil-element level and outputs detailed predictions for temperature changes, pore water behaviour, ground stresses and deformation in and around geotechnical structures. Applications of these tools to specific problems set in Eastern Siberia and pipeline heave tests are illustrated.

    Cold regions, which are expected to suffer particularly severe future climate effects, will pose very challenging geotechnical conditions in the 21st century involving ground freezing and thawing. Given the uncertainty of future environmental changes and the vast expanses of the cold regions, it is appropriate to address problems such as pipeline or road construction with analytical methods that have multiple scales and layers. High- and middle-level predictive tools are described that integrate climatic predictions from AOGCMs and their down-scaling schemes, geological and topographical (DEM) information, remotely-sensed vegetation data and non-linear finite element analysis for soil freezing and thawing. These tools output broad scale predictions of geothermal responses, at a regional scale, that offer hazard zoning schemes related to permafrost thawing. A more intensive localscale predictive tool is then outlined that considers fully-coupled thermo-hydro-mechanical processes occurring at the soil-element level and outputs detailed predictions for temperature changes, pore water behaviour, ground stresses and deformation in and around geotechnical structures. Applications of these tools to specific problems set in Eastern Siberia and pipeline heave tests are illustrated.

  • Coupled modelling of barriers for radioactive waste disposal

     Gens Sole, Antonio
    International Symposium on Coupled Phenomena in Environmental Geotechnics
    Presentation's date: 2013-07
    Presentation of work at congresses

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    The paper first presents an overview of the issues associated with radioactive waste disposal and follows with a brief description of deep geological disposal for high level radioactive waste. The performance assessment of these underground repositories requires a good understanding of the basic phenomena that affect the succession of barriers separating the waste from the biosphere. A key safety element in the design of these facilities is an engineered barrier, made up of highly expansive clay, that surrounds the canister containing the waste. This barrier is subjected to a complex set of coupled thermo-hydro-mechanical (THM) phenomena that must be correctly modelled and understood. The paper presents a coupled THM formulation that incorporates the most relevant processes occurring in the barrier and their mutual interactions. The formulation is then applied to the modelling of an in situ test that simulates repository conditions at full scale. The tests involves heating and hydration of the engineered barrier. It is shown that the modelling results represent satisfactorily the observations from the test, including those obtained dafter a partial dismantling stage. This exercise demonstrates that the basic phenomena appear to be well understood and that the formulation and associated computer code are useful tools for the coupled analysis of this type of THM processes.

    The paper first presents an overview of the issues associated with radioactive waste disposal and follows with a brief description of deep geological disposal for high level radioactive waste. The performance assessment of these underground repositories requires a good understanding of the basic phenomena that affect the succession of barriers separating the waste from the biosphere. A key safety element in the design of these facilities is an engineered barrier, made up of highly expansive clay, that surrounds the canister containing the waste. This barrier is subjected to a complex set of coupled thermo-hydro-mechanical (THM) phenomena that must be correctly modelled and understood. The paper presents a coupled THM formulation that incorporates the most relevant processes occurring in the barrier and their mutual interactions. The formulation is then applied to the modelling of an in situ test that simulates repository conditions at full scale. The tests involves heating and hydration of the engineered barrier. It is shown that the modelling results represent satisfactorily the observations from the test, including those obtained dafter a partial dismantling stage. This exercise demonstrates that the basic phenomena appear to be well understood and that the formulation and associated computer code are useful tools for the coupled analysis of this type of THM processes.

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    THMC modelling of jet grouting  Open access

     Gesto, Jose M; Gens Sole, Antonio; Arroyo Alvarez de Toledo, Marcos
    International Conference on Computational Plasticity Fundamentals and Applications
    Presentation's date: 2013-09
    Presentation of work at congresses

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    A framework for the study of the jet-grouting hydration reaction and of the associated thermo-hydro-mechanical and chemical (THMC) interactions with the surrounding soils has been developed. In this work, we summarize the basic formulation that may be used for the simulation of such interactions, including references to the balance equations governing the problem, to the release of heat during the curing of the jet-grouted mass, to the TMC behaviour of such material and to the THM behaviour of the surrounding soil. The approach presented falls within the framework of plasticity for saturated soils, and it has been implemented within a FEM code for the study of the potential effects of the THMC couplings associated to jet-grouting treatments. The results obtained with this program validate it as a proper tool for the systematic analysis of a number of questions of interest in engineering practice, allowing the assessment, among others, of the following issues: magnitude and rate of production of the thermo-plastic settlements caused by the heat release associated to the installation of jet-grouted columns in the soil; effects of the release of the hydration heat on the hydraulic conditions in the surrounding soil; effects of the boundary conditions, the relative position of the jet-grouted zones and its sequence of installation on the rate of increase of the stiffness and strength associated to the curing of the jet-grouted zones; effects of those factors on the impact of the heat release on the surrounding soils.

    A framework for the study of the jet-grouting hydration reaction and of the associated thermo-hydro-mechanical and chemical (THMC) interactions with the surrounding soils has been developed. In this work, we summarize the basic formulation that may be used for the simulation of such interactions, including references to the balance equations governing the problem, to the release of heat during the curing of the jet-grouted mass, to the TMC behaviour of such material and to the THM behaviour of the surrounding soil. The approach presented falls within the framework of plasticity for saturated soils, and it has been implemented within a FEM code for the study of the potential effects of the THMC couplings associated to jet-grouting treatments. The results obtained with this program validate it as a proper tool for the systematic analysis of a number of questions of interest in engineering practice, allowing the assessment, among others, of the following issues: magnitude and rate of production of the thermo-plastic settlements caused by the heat release associated to the installation of jet-grouted columns in the soil; effects of the release of the hydration heat on the hydraulic conditions in the surrounding soil; effects of the boundary conditions, the relative position of the jet-grouted zones and its sequence of installation on the rate of increase of the stiffness and strength associated to the curing of the jet-grouted zones; effects of those factors on the impact of the heat release on the surrounding soils.

  • The effect of radial walls on CPT in a DEM-based virtual calibration chamber

     Arroyo Alvarez de Toledo, Marcos; Butlanska, Joanna; Gens Sole, Antonio; O'Sullivan, C.
    International Symposium on Computational Geomechanics
    Presentation's date: 2013-08
    Presentation of work at congresses

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  • Shallow foundations for offshore wind towers

     Arroyo Alvarez de Toledo, Marcos; Abadías, D.; Alcoverro, J.; Gens Sole, Antonio
    International Conference on Soil Mechanics and Geotechnical Engineering
    Presentation's date: 2013-09
    Presentation of work at congresses

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    Direct foundations are present in about 25% of the installed offshore wind power towers. The peculiarities of this type of structure are well known: high dynamic sensitivity, complex couplings between environmental actions, machine operation and structural response, complex installation and maintenance, difficult site investigation. There is a clear need for optimized foundation design tools that would enable cost reduction and a more detailed assessment of the risk of every installation. One such tool is likely to be the systematic use of failure envelopes for capacity checks. The paper explores the benefits of such an approach with various realistic design examples.

    Direct foundations are present in about 25% of the installed offshore wind power towers. The peculiarities of this type of structure are well known: high dynamic sensitivity, complex couplings between environmental actions, machine operation and structural response, complex installation and maintenance, difficult site investigation. There is a clear need for optimized foundation design tools that would enable cost reduction and a more detailed assessment of the risk of every installation. One such tool is likely to be the systematic use of failure envelopes for capacity checks. The paper explores the benefits of such an approach with various realistic design examples.

  • Determination of the thermal parameters of a clay from heating cell tests

     Romero Morales, Enrique Edgar; Lima Amorim, Analice França; Gens Sole, Antonio; Vaunat, Jean; Li, X. L.
    International Conference on Soil Mechanics and Geotechnical Engineering
    Presentation's date: 2013-09
    Presentation of work at congresses

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    Boom Clay is being studied in Belgium in connection with the design of a repository for radioactive waste. Within this context, thermal impact may play an important role on the behaviour of this low-permeability clay. To evaluate this impact, heating pulse tests on intact borehole samples were carried out using an axi-symmetric and constant volume heating cell with controlled hydraulic boundary conditions. Attention is focused on the time evolution of temperature and pore water pressure changes along heating and cooling paths ¿i.e., pore pressure build-up during quasi-undrained heating and later dissipation to the applied hydraulic boundary conditions¿. A coupled thermo-hydro-mechanical finite element program was used in a first stage to determine thermal parameters by back-analysis and then to simulate the experimental results.

    Boom Clay is being studied in Belgium in connection with the design of a repository for radioactive waste. Within this context, thermal impact may play an important role on the behaviour of this low-permeability clay. To evaluate this impact, heating pulse tests on intact borehole samples were carried out using an axi-symmetric and constant volume heating cell with controlled hydraulic boundary conditions. Attention is focused on the time evolution of temperature and pore water pressure changes along heating and cooling paths –i.e., pore pressure build-up during quasi-undrained heating and later dissipation to the applied hydraulic boundary conditions–. A coupled thermo-hydro-mechanical finite element program was used in a first stage to determine thermal parameters by back-analysis and then to simulate the experimental results.

  • Numerical simulation of a shallow foundation on an unsaturated silt

     González, N.A.; Gens Sole, Antonio
    Pan-American Conference on Unsaturated Soils
    Presentation's date: 2013
    Presentation of work at congresses

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    This paper presents a coupled flow-deformation finite element analysis of a shallow foundation on an unsaturated loosely compacted silt subjected to variations in the water level. The behaviour of the silt foundation was simulated using the Barcelona Basic Model (BBM) which was implemented into the PLAXIS finite element code. Material parameters were calibrated from laboratory tests reported in the literature. The influence of partial soil saturation and of fluctuations of the groundwater level on the behaviour of footing is investigated. Constitutive equations were solved using two stress integration procedures, an explicit stress integration scheme with automatic substepping and error control techniques and a fully implicit stress integration scheme based on the Backward-Euler algorithm with substepping. Their performances during the numerical simulation are evaluated

  • Coupled phenomena induced by freezing in a granular material

     Casini, Francesca; Gens Sole, Antonio; Olivella Pastalle, Sebastian; Viggiani, Giulia M.B.
    International Symposium on Coupled Phenomena in Environmental Geotechnics
    Presentation's date: 2013-07
    Presentation of work at congresses

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    Artificial Ground Freezing (AGF) is a controllable process that can be used by engineers to stabilise temporarily the ground, provide structural support and/or exclude groundwater from an excavation until construction of the final lining provides permanent stability and water tightness. AGF is often carried out based on an observational approach, while a full understanding of the freezing process and of the generation of freezing-induced heave and settlements is still far from being achieved. In this work, the process of ground freezing is studied using a constitutive model that encompasses frozen and unfrozen behaviour within a unified effective-stress-based framework and employs a combination of ice pressure, liquid water pressure and total stress as state variables. The parameters of the constitutive model are calibrated against experimental data obtained from samples retrieved during construction of Napoli underground, in which AGF was extensively used to excavate in granular soils and weak fractured rock below the ground water table.

    Artificial Ground Freezing (AGF) is a controllable process that can be used by engineers to stabilise temporarily the ground, provide structural support and/or exclude groundwater from an excavation until construction of the final lining provides permanent stability and water tightness. AGF is often carried out based on an observational approach, while a full understanding of the freezing process and of the generation of freezing-induced heave and settlements is still far from being achieved. In this work, the process of ground freezing is studied using a constitutive model that encompasses frozen and unfrozen behaviour within a unified effective-stress-based framework and employs a combination of ice pressure, liquid water pressure and total stress as state variables. The parameters of the constitutive model are calibrated against experimental data obtained from samples retrieved during construction of Napoli underground, in which AGF was extensively used to excavate in granular soils and weak fractured rock below the ground water table.

  • Analysis of tunnel excavation in London Clay incorporating soil structure

     González, Nubia A.; Rouainia, Mohamed; Arroyo Alvarez de Toledo, Marcos; Gens Sole, Antonio
    Géotechnique
    Date of publication: 2012-08
    Journal article

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  • Interpretation of unsaturated soil behaviour in the stress. Saturation space, I: volume change and water retention behaviour

     Zhou, Nan; Sheng, Daichao; Scott, Sloan; Gens Sole, Antonio
    Computers and geotechnics
    Date of publication: 2012-06
    Journal article

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  • Interpretation of unsaturated soil behaviour in the stress-saturation space. II: Constitutive relationships and validations

     Zhou, Anna N.; Sheng, Daichao; Sloan, S.W.; Gens Sole, Antonio
    Computers and geotechnics
    Date of publication: 2012-06
    Journal article

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  • THM analysis of a large-scale heating test incorporating material fabric changes

     Sánchez, Marcelo; Gens Sole, Antonio; Olivella Pastalle, Sebastian
    International journal for numerical and analytical methods in geomechanics
    Date of publication: 2012-03
    Journal article

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  • Thermal-hydraulic-mechanical (THM) behaviour of a large-scale in situ heating experiment during cooling and dismantling

     Sánchez, M.; Gens Sole, Antonio; Guimarães, Leonardo do N
    Canadian geotechnical journal
    Date of publication: 2012-10-10
    Journal article

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  • Compacted soil behaviour: initial state, structure and constitutive modelling

     Alonso Pérez de Agreda, Eduardo; Pinyol Puigmarti, Nuria Merce; Gens Sole, Antonio
    Géotechnique
    Date of publication: 2012-11
    Journal article

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    The paper explores the behaviour of compacted soils throughout the (dry density-water content) compaction plane by means of a conceptual framework that incorporates microstructural information. The engineering properties of compacted soils are described by an initial state in terms of a yielding stress, soil suction and a microstructural state variable. Microstructure is defined by the ratio of microvoid volume to total void volume. The pattern of variation of the microstructural parameter within the compaction plane has been determined, for some compacted soils, by analysing mercury intrusion porosimetry data. The microstructure of wet and dry compaction conditions can then be quantified. To ensure consistency, the framework is cast in the form of a constitutive model defined in terms of an effective suction and a constitutive stress that incorporate the microstructural variable...

  • Thermal conductivity of argillaceous rocks: determination methodology using in situ heating tests

     Garitte, Benoit; Gens Sole, Antonio; Vaunat, Jean; Gilles, Armand
    Rock mechanics and rock engineering
    Date of publication: 2012-11-12
    Journal article

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    This study focuses on the characterisation of thermal conductivity for three potential host rocks for radioactive waste disposal. First, the heat conduction process is reviewed on the basis of an analytical solution and key aspects related to anisotropic conduction are discussed. Then the existing information on the three rocks is summarised and a broad uncertainty range of thermal conductivity is estimated based on the mineralogical composition. Procedures to backanalyse the thermal conductivity on the basis of in situ heating tests are assessed and a methodology is put forward. Finally, this methodology is used to estimate the impact of experimental uncertainties and applied to the four in situ heating tests. In the three potential host rocks, a clear influence of the bedding planes was identified and anisotropic heat conduction was shown to be necessary to interpret the observed temperature field. Experimental uncertainties were also shown to induce a larger uncertainty on the anisotropy ratio than on the equivalent thermal conductivity defined as the geometric mean of the thermal conductivity in the three principal directions.

  • Simulation of cement-improved clay structures with a bonded elasto-plastic model: A practical approach

     Arroyo Alvarez de Toledo, Marcos; Ciantia, Matteo; Castellanza, Riccardo; Gens Sole, Antonio; Nova, Roberto
    Computers and geotechnics
    Date of publication: 2012-09
    Journal article

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

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

  • Numerical modeling of delayed and progressive failure in stiff clays with two-stage softening behaviour  Open access

     Zhan, Zhifeng
    Defense's date: 2012-06-19
    Universitat Politècnica de Catalunya
    Theses

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    Based on the laboratory, field and numerical results, the post-rupture strength defined firstly by Burland (1990) is verified and introduced in this thesis to describe the two-stage post-peak strain-softening characteristics of stiff clays. The first softening stage is induced by the loss of interbonding between particles, i.e. the cohesive component of strength at relatively small displacement and hence termed as cementation loss; while the second is due to the gradual realignment, i.e. reorientation of clay particles at large displacements and can be called as gradual frictional resistance loss. A generalised constitutive model is then established to simulate the two-stage softening characteristics of stiff clays by modifying the Mohr-Coulomb model. This model is formulated and then implemented into an explicit finite difference program FLAC. The new model is applied to simulate laboratory tests such as triaxial compression tests and direct shear box test to depict the new model. The numerical results demonstrate the capability and efficiency of the modified softening model to model the two-stage strain-softening behaviour of stiff clays. A series of analyses of delayed progressive failure of cut slopes in stiff clays have been performed using two-stage softening model incorporating post-rupture strength. The numerical results reproduce well the progressive failure process, position of failure surface and failure time, which proves further the validity of the new model. Meanwhile, parametric analyses are also carried out to demonstrate the general influence of post-rupture strength. The results demonstrate that the slope stability with the adoption of two-stage softening model is reduced compared with that using one-stage softening model due to the quicker cohesion reduction with deviatoric plastic strain in the first softening stage of two-stage softening model. Both post-rupture strength concept and two-stage softening model are applied to the modelling of a famous case¿ Aznalcóllar dam failure under both inhomogeneous and homogeneous hypotheses. The simulations reproduced well the failure of Aznalcóllar dam including the location and shape of the slip surface, the progressive failure course and the development of pore water pressure in terms of the developments of shear strain rate, shear strain increment, displacement, velocity and strength parameter softening. The mechanism of Aznalcóllar dam failure is deemed to be progressive failure mainly due to the softening of Guadalquivir blue clay. The developments of average stress ratio, average residual factor, average brittleness, average stress path, the distribution of shear stress and mobilised strength parameters along the slip surface confirm further the mechanism of progressive failure of Aznalcóllar dam with these values to be intermediate between peak and residual values during the failure course. The post-rupture state could be thought as the average one at initial failure. At final failure, most part of the slip surface is at residual state, especially along the horizontal part. The Aznalcóllar dam failure is sensitive to the softening rate. Larger rates will induce earlier failure and no failure will occur with slow softening rates. Only an appropriate setting of softening rates can cause failure at final phase under both inhomogeneous and homogeneous hypotheses. Finally, the post-rupture concept is introduced to derive analytical solutions to limit pressure, the stress, strain, and displacement fields for the cylindrical cavity expansion in stiff overconsolidated clay. The results of computational examples and the similarity between numerical solution and analytical one verify the reasonableness of the analytical solution to cavity expansion in stiff clays with two-stage softening characteristics.

    Basado en los datos de laboratorio y de campo y los resultados numéricos, la resistencia post-ruptura definida por Burland (1990) se verifica y introduce para describir las dos etapas de ablandamiento post-ruptura de las arcillas rígidas. La primera etapa del ablandamiento está inducida por la pérdida de inter-conexión entre las partículas, o de la componente cohesiva de la resistencia a desplazamientos relativamente pequeños; la segunda etapa es debida al realineamiento gradual o reorientación de las partículas de arcilla a grandes desplazamientos y se puede llamar como pérdida gradual de la resistencia friccional. Se establece un modelo constitutivo general para simular las características de ablandamiento en dos etapas de las arcillas rígidas, modificando el modelo Mohr-Coulomb. La formulación de este modelo es ilustrada detalladamente y luego implementada en un programa explícito de diferencia finitas FLAC. Se aplica el nuevo modelo para simular los ensayos de laboratorio como ensayos de compresión triaxial y ensayos de corte directo. Los resultados numéricos demuestran la capacidad y eficiencia del modelo modificado de ablandamiento para reproducir el comportamiento de ablandamiento por deformación en dos etapas de las arcillas rígidas. Se han realizado una serie de análisis de la rotura progresiva diferida de taludes en arcillas rígidas, utilizando el nuevo modelo de ablandamiento en dos etapas con incorporación de la resistencia de post-ruptura. Los resultados numéricos reproducen bastante bien el proceso progresivo de la rotura, la posición de la superficie de rotura y el tiempo de rotura, lo cual brinda validez adicional al nuevo modelo. Adicionalmente, se ha llevado a cabo un análisis paramétrico para demostrar la influencia general de la resistencia de post-ruptura. Los resultados demuestran que se reduce la estabilidad de los taludes con la adopción del modelo de ablandamiento de dos etapas en comparación con lo de solo una etapa, debido a la reducción más rápida de la cohesión con la deformación plástica en primera fase de ablandamiento del modelo de ablandamiento de dos etapas. El concepto de la resistencia post-ruptura y el modelo de ablandamiento en dos etapas son aplicados en la simulación numérica del famoso caso de la rotura de la presa de Aznalcóllar bajo las dos hipótesis no homogéneos y homogénea. Las simulaciones reproducen bien la rotura de la presa de Aznalcóllar incluyendo el proceso progresivo de la rotura, la ubicación y la forma de la superficie de deslizamiento y el desarrollo de la presión del agua en los poros, según el desarrollo del estado de la plasticidad, la velocidad de la deformación de corte, el incremento de la deformación de corte, el desplazamiento, la velocidad y parámetros de resistencia del ablandamiento. El desarrollo de la relación media de las tensiones, el factor residual, la fragilidad media, la trayectoria de tensiones media y la distribución de las tensiones de corte movilizadas y los parámetros de resistencia movilizados a lo largo de la superficie de deslizamiento, confirman el mecanismo de rotura progresiva de la presa de Aznalcóllar debida principalmente al ablandamiento de la masa de arcilla azul del Guadalquivir, con estos valores en el intermedio entre los valores pico y residual durante el proceso de la rotura. La rotura de la presa de Aznalcóllar es sensible a la velocidad de ablandamiento de la deformación de corte plástica. Finalmente, se introduce el concepto de la resistencia post-ruptura de las arcillas rígidas para derivar las soluciones analíticas para la presión límite, las tensiones, las deformaciones y campos de desplazamientos de la expansión de cavidades cilíndricas en arcillas rígidas. Los resultados de los ejemplos de cálculo y la similitud entre la solución numérica y analítica verifican la razonabilidad de la solución analítica a la expansión de la cavidad en arcillas rígidas con las características de ablandamiento de dos etapas.

  • Numerical Modelling of Artificial Ground Freezing

     Gens Sole, Antonio
    Participation in a competitive project

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  • Conminución granular y resistencia de interfase: aplicación da los pilotes off-shore

     Gens Sole, Antonio
    Participation in a competitive project

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