Olivella Pastalle, Sebastian
Total activity: 340
Professional category
Researcher
Doctoral courses
Doctor Enginyer de Camins, Canals i Ports
University degree
Enginyer de Camins, Canals i Ports
Research group
MSR - Soil and Rock Mechanics
Department
Department of Geotechnical Engineering and Geo-Sciences
School
Barcelona School of Civil Engineering (ETSECCPB)
E-mail
sebastia.olivellaupc.edu
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Orcid
0000-0003-3976-4027 Open in new window
Scopus Author ID
7003267464 Open in new window
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1 to 50 of 340 results
  • Long term impacts of cold CO2 injection on the caprock integrity

     Vilarrasa Riaño, Victor; Olivella Pastalle, Sebastian; Carrera Ramírez, Jesús; Rutqvist, Jonny
    International journal of greenhouse gas control
    Date of publication: 2014-05
    Journal article

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    Carbon dioxide (CO2) will reach the storage formation at a temperature lower than that of the reservoir, especially for high flow rates. Thus, thermo-mechanical effects might jeopardize the caprock mechanical stability and cause induced seismicity. We perform thermo-hydro-mechanical simulations of cold (liquid) CO2 injection and analyze the impacts on the rock mechanical stability during a 30 year injection period. Injection of cold CO2 develops a cold region around the injection well that induces a thermal stress reduction in the reservoir due to its contraction. Stress redistribution, which occurs to satisfy stress equilibrium and displacement compatibility, causes the horizontal total stress to increase in the lower portion of the caprock. The thermal stress reduction in the reservoir decreases its stability when injecting a constant mass flow rate through a vertical well in normal faulting stress regimes. Such decrease in stability, if sufficiently large, might cause induced seismicity as well as enhancing reservoir permeability and injectivity. However, the caprock tightens due to the increase in horizontal total stress, improving its stability. After a significant improvement in caprock stability during the first years of injection, stability decreases gradually for longer injection times, but the stress state remains more stable than prior to injection, even for stiff caprocks. By contrast, in a reverse faulting stress regime, both the reservoir and the caprock are less stable during the first years of injection, but stability improves subsequently. On the other hand, injecting cold CO2 at a constant mass flow rate through a horizontal well does not significantly affect the caprock stability for the scenarios considered in this study (in both normal and reverse faulting stress regimes). We show that accounting for the thermal expansion of the grains is very important in low porosity formations to avoid simulating artificial porosity and total stress reductions in the cooled region of the caprock that yield unreal high mobilized friction angles in the lower part of the caprock in normal faulting stress regimes. Overall, injecting cold CO2 should not be feared because of the thermal stresses reduction, though care should be taken to avoid excessive induced seismicity. Published by Elsevier Ltd.

  • Osmosis-induced water uptake by Eurobitum bituminized radioactive waste and pressure development in constant volume conditions

     Mariën, An; Mokni, Nadia; Valcke, Elie; Olivella Pastalle, Sebastian; Smets, Esteven; Li, Xiangling
    Journal of nuclear materials
    Date of publication: 2013-01
    Journal article

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    he chemo-hydro-mechanical (CHM) interaction between swelling Eurobitum radioactive bituminized waste (BW) and Boom Clay is investigated to assess the feasibility of geological disposal for the long-term management of this waste. These so-called compatibility studies include laboratory water uptake tests at the Belgian Nuclear Research Center SCK.CEN, and the development of a coupled CHM formulation for Eurobitum by the International Center for Numerical Methods and Engineering (CIMNE, Polytechnical University of Cataluna, Spain). In the water uptake tests, the osmosis-induced swelling, pressure increase and NaNO3 leaching of small cylindrical BW samples (diameter 38 mm, height 10 mm) is studied under constant total stress conditions and nearly constant volume conditions; the actual geological disposal conditions should be intermediate between these extremes...

  • Gas flow in anisotropic claystone: modelling triaxial experiments

     Arnedo Gaute, Diego; Alonso Pérez de Agreda, Eduardo; Olivella Pastalle, Sebastian
    International journal for numerical and analytical methods in geomechanics
    Date of publication: 2013-10
    Journal article

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    Selected gas pulse tests on initially saturated claystone samples under isotropic confinement pressure are simulated using a 3D thermo-hydro-mechanical code. The constitutive model considers the hydro-mechanical anisotropy of argillaceous rocks. A cross-anisotropic linear elastic law is adopted for the mechanical behaviour. Elements for a proper modelling of gas flow along preferential paths include an embedded fracture permeability model. Rock permeability and its retention curve depend on strains through a fracture aperture. The hydraulic and mechanical behaviours have a common anisotropic structure. Small-scale heterogeneity is considered to enhance the initiation of flow through preferential paths, following the direction of the bedding planes. The numerical simulations were performed considering two different bedding orientations, parallel and normal to the imposed flow in the test. Simulations are in agreement with recorded upstream and downstream pressures in the tests. The evolution of fluid pressures, degree of saturation, element permeability and stress paths are presented for each case analysed. This information provides a good insight into the mechanisms of gas transport. Different flow patterns are obtained depending on bedding orientation, and the results provide an explanation for the results obtained in the tests.

  • Thermo-hydraulic behaviour of the vadose zone in sulphide tailings at Iberian Pyrite Belt: waste characterization, monitoring and modelling

     Blanco, Alejandro; Lloret Morancho, Antonio; Carrera Ramírez, Jesús; Olivella Pastalle, Sebastian
    Engineering geology
    Date of publication: 2013-10
    Journal article

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    Unsaturated conditions favour the oxidation of sulphide minerals from mine wastes, which results in the release of contaminant products into groundwater. An abandoned high-sulphide impoundment in the Iberia Pyritic Belt, wherein tailings have undergone oxidation for more than 28. years, was investigated for hydrological purposes. The objective was to understand the interactions between those mining tailings and the atmosphere under natural semiarid conditions (wet and dry seasons, short intensive rain events and strong daily temperature differences during the dry season).After the deposition, the sequence of waste textures that results from the sedimentation process is strongly dependent on the distance to discharge point. The spatial continuity of the sedimentation layers was studied by means of small scale dynamic penetration tests.The thermo-hydraulic characterization of the waste includes the determination of the water retention curve, saturated and unsaturated permeability, pore size distribution and thermal properties for the different textures.Atmospheric and waste physical measures, from 2002 to 2006, were performed using different techniques. The important changes in the salinity of the waste avoided the use of a single calibration for the electromagnetic sensors; a valid alternative was the evaluation of the water content from thermal conductivity estimations.Finally, a numerical model using the HYDRUS-1D software is presented. Model results reasonably fit the in-situ measures of soil moisture, soil temperature, soil water potential and soil heat flux in the vadose zone of tailings impoundment. Moreover, they provide information for energy and water balance determinations.

  • 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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  • A constitutive law for rock joints considering the effects of suction and roughness on strength parameters

     Zandarín Iragorre, Maria Teresa; Alonso Pérez de Agreda, Eduardo; Olivella Pastalle, Sebastian
    International journal of rock mechanics and mining sciences (1997)
    Date of publication: 2013-06
    Journal article

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    The paper describes a set of experiments aimed at investigating suction effects on the shear behaviour of rock discontinuities. The experimental investigation focused on the effects of suction on the mechanical behaviour of rock joints. Laboratory tests were performed in a direct shear cell equipped with suction control. Suction was imposed using a forced vapour convection circuit connected to the cell and controlled by an air pump. Artificial joints of Lilla claystone were prepared. Joint roughness of varying intensity was created by carving the surfaces in contact in such a manner that rock ridges of different tip angles were formed. These angles ranged from 0° (smooth joint) to 45° (very rough joint profile). The geometric profiles of the two surfaces in contact were initially positioned in a ¿matching¿ situation...

  • Liquid CO2 injection for geological storage in deep saline aquifers

     Vilarrasa Riaño, Victor; Silva Rojas, Orlando Enrique; Olivella Pastalle, Sebastian; Carrera Ramírez, Jesús
    International journal of greenhouse gas control
    Date of publication: 2013-05
    Journal article

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    CO2 will remain in supercritical (SC) state (i.e. p > 7.382 MPa and T > 31.04 °C) under the pressure (p) and temperature (T) conditions appropriate for geological storage. Thus, it is usually assumed that CO2 will reach the aquifer in SC conditions. However, inflowing CO2 does not need to be in thermal equilibrium with the aquifer. In fact, surface operations are simpler for liquid than for SC CO2, because CO2 is transported in liquid state. Yet, problems might arise because of thermal stresses induced by cold CO2 injection and because of phase changes in the injection tubing or in the formation. Here, we propose liquid CO2 injection and analyze its evolution and the thermo-hydro-mechanical response of the formation and the caprock. We find that injecting CO2 in liquid state is energetically more efficient than in SC state because liquid CO2 is denser than SC CO2, leading to a lower overpressure not only at the wellhead, but also in the reservoir because a smaller fluid volume is displaced. Cold CO2 injection cools down the formation around the injection well. Further away, CO2 equilibrates thermally with the medium in an abrupt front. The liquid CO2 region close to the injection well advances far behind the SC CO2 interface. While the SC CO2 region is dominated by gravity override, the liquid CO2 region displays a steeper front because viscous forces dominate (liquid CO2 is not only denser, but also more viscous than SC CO2). The temperature decrease close to the injection well induces a stress reduction due to thermal contraction of the media. This can lead to shear slip of pre-existing fractures in the aquifer for large temperature contrasts in stiff rocks, which could enhance injectivity. In contrast, the mechanical stability of the caprock is improved in stress regimes where the maximum principal stress is the vertical.

  • Hydromechanical characterization of CO2 injection sites

     Vilarrasa Riaño, Victor; Carrera Ramírez, Jesús; Olivella Pastalle, Sebastian
    International journal of greenhouse gas control
    Date of publication: 2013-11
    Journal article

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    Clear understanding of coupled hydromechanical effects, such as ground deformation, induced microseismicity and fault reactivation, will be crucial to convince the public that geologic carbon storage is secure. These effects depend on hydromechanical properties, which are usually determined at metric scale. However, their value at the field scale may differ in orders of magnitude. To address this shortcoming, we propose a hydromechanical characterization test to estimate the hydromechanical properties of the aquifer and caprock at the field scale. We propose injecting water at high pressure and, possibly, low temperature while monitoring fluid pressure and rock deformation. Here, we analyze the problem and perform numerical simulations and a dimensional analysis of the hydromechanical equations to obtain curves for overpressure and vertical displacement as a function of the volumetric strain term. We find that these curves do not depend much on the Poisson ratio, except for the dimensionless vertical displacement at the top of the caprock, which does. We can then estimate the values of the Young's modulus and the Poisson ratio of the aquifer and the caprock by introducing field measurements in these plots. Hydraulic parameters can be determined from the interpretation of fluid pressure evolution in the aquifer. Reverse-water level fluctuations are observed, i.e. fluid pressure drops in the caprock as a result of the induced deformation that undergoes the aquifer-caprock system when injecting in the aquifer. We find that induced microseismicity is more likely to occur in the aquifer than in the caprock and depends little on their stiffness. Monitoring microseismicity is a useful tool to track the opening of fractures. The propagation pattern depends on the stress regime, i.e. normal, strike slip or reverse faulting. The onset of microseismicity in the caprock can be used to define the maximum sustainable injection pressure to ensure a permanent CO2 storage. (C) 2012 Elsevier Ltd. All rights reserved.

  • 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.

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    Modelling 3D mechanics interfaces with continuum elements  Open access

     Puig Damians, Ivan; Olivella Pastalle, Sebastian; Lloret Morancho, Antonio; Josa Garcia-tornel, Alejandro; Bathurst, Richard
    Workshop of CODE-BRIGHT Users
    Presentation's date: 2013-05-07
    Presentation of work at congresses

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    This document presents preliminary results of FEM-numerical analysis of soilreinforcement pullout tests. The numerical model has been developed with CODE_BRIGHT and assuming the interfaces as continuum materials. The results of the preliminary parametric analyses described herein provide useful information on the shear behavior modeling of soil-reinforcement strip interfaces under working stress conditions

    This document presents preliminary results of FEM-numerical analysis of soil-reinforcement pullout tests. The numerical model has been developed with CODE_BRIGHT and assuming the interfaces as continuum materials. The results of the preliminary parametric analyses described herein provide useful information on the shear behavior modeling of soil-reinforcement strip interfaces under working stress conditions.

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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.

  • Reinventing civil engineering studies in Spain to face new challenges

     Lozano Galant, Jose Antono; Ruiz Ripoll, Lidia; Olivella Pastalle, Sebastian; Turmo Coderque, Jose
    EUCEET Association Conference
    Presentation's date: 2013-10-14
    Presentation of work at congresses

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  • 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.

  • Impacts of cold CO2 injection in deep saline aquifers on the rock mechanical integrity.

     Vilarrasa Riaño, Victor; Carrera Ramírez, Jesús; SILVA, ORLANDO; Olivella Pastalle, Sebastian
    US Rock Mechanics / Geomechanics Symposium
    Presentation's date: 2013-06-25
    Presentation of work at congresses

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    Injecting CO2 into aquifers at depths greater than 800 m brings CO2 to a supercritical state where its density is large enough to ensure an efficient use of pore space. However, CO2 may not be in thermal equilibrium with the medium when it enters the reservoir because pressure and temperature injection conditions at the wellhead can be diverse and CO2 will not equilibrate with the geothermal gradient if the flow rate is high. This is especially true when injecting liquid, i.e. cold, CO2, which is highly advantageous from the point of view of demanded compression energy. In such case, thermal stress changes will be induced, which will affect rock stability. Coupled thermo-hydro-mechanical simulations of CO2 injection produce a region around the injection well in thermal equilibrium with the injected CO2. Further away, CO2 thermally equilibrates with the medium in an abrupt front. Thermal contraction of the reservoir can lead to shear slip of pre-existing fractures, triggering microseismic events, for large temperature contrasts in stiff rocks, which could enhance injectivity. In contrast, the mechanical stability of the caprock is improved in stress regimes where the maximum principal stress is the vertical.

    Injecting CO2 into aquifers at depths greater than 800 m brings CO2 to a supercritical state where its density is large enough to ensure an efficient use of pore space. However, CO2 may not be in thermal equilibrium with the medium when it enters the reservoir because pressure and temperature injection conditions at the wellhead can be diverse and CO2 will not equilibrate with the geothermal gradient if the flow rate is high. This is especially true when injecting liquid, i.e. cold, CO2, which is highly advantageous from the point of view of demanded compression energy. In such case, thermal stress changes will be induced, which will affect rock stability. Coupled thermo-hydro-mechanical simulations of CO2 injection produce a region around the injection well in thermal equilibrium with the injected CO2. Further away, CO2 thermally equilibrates with the medium in an abrupt front. Thermal contraction of the reservoir can lead to shear slip of pre-existing fractures, triggering microseismic events, for large temperature contrasts in stiff rocks, which could enhance injectivity. In contrast, the mechanical stability of the caprock is improved in stress regimes where the maximum principal stress is the vertical.

  • Rapid drawdown in embankment dams

     Pinyol Puigmarti, Nuria Merce; Alonso Pérez de Agreda, Eduardo; Olivella Pastalle, Sebastian
    Date of publication: 2012
    Book chapter

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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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  • Crack patterns in clayey soils: experiments and modeling

     Trabelsi, H; Jamei, M.; Zenzri, H.; Olivella Pastalle, Sebastian
    International journal for numerical and analytical methods in geomechanics
    Date of publication: 2012-08-10
    Journal article

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  • FEBEXe project: progress report

     Gens Sole, Antonio; Olivella Pastalle, Sebastian
    Date: 2012-04-04
    Report

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  • High pressure injection test for hydromechanical and onset of induced microseismicity characterization of CO2 injection sites

     Vilarrasa Riaño, Victor; Carrera Ramírez, Jesús; Olivella Pastalle, Sebastian
    European Geosciences Union General Assembly
    Presentation's date: 2012-04
    Presentation of work at congresses

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  • Environmental effects on earth embankments

     Olivella Pastalle, Sebastian; Alonso Pérez de Agreda, Eduardo
    Date of publication: 2012
    Book chapter

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  • Thermo-Hydro-Mechanical Impacts of Carbon Dioxide (CO2) Injection in Deep Saline Aquifers.  Open access

     Vilarrasa Riaño, Victor
    Defense's date: 2012-07-20
    Universitat Politècnica de Catalunya
    Theses

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    Los procesos termo-hidro-mecánicos relacionados con el almacenamiento geológico de carbono deben ser entendidos y cuantificados para demostrar a la opinión pública de que la inyección de dióxido de carbono (CO2) es segura. Esta Tesis tiene como objetivo mejorar dicho conocimiento mediante el desarrollo de métodos para: (1) evaluar la evolución tanto de la geometría de la pluma de CO2 como de la presión de los fluidos; (2) definir un ensayo de campo que permita caracterizar la presión de inyección máxima sostenible y los parámetros hidromecánicos de las rocas sello y almacén; y (3) proponer un nuevo concepto de inyección que es energéticamente eficiente y que mejora la estabilidad de la roca sello en la mayoría de escenarios geológicos debido a efectos termo-mecánicos. modelo viscoplástico. Las simulaciones ilustran que, dependiendo de las condiciones de contorno, el momento más desfavorable ocurre al inicio de la inyección. Sin embargo, si los contornos son poco permeables, la presión de fluido continúa aumentando en todo el acuífero, lo que podría llegar a comprometer la estabilidad de la roca sello a largo plazo. Para evaluar dichos problemas, proponemos un ensayo de caracterización hidromecánica a escala de campo para estimar las propiedades hidromecánicas de las rocas sello y almacén. Obtenemos curvas para la sobrepresión y el desplazamiento vertical en función del término de la deformación volumétrica obtenido del análisis adimensional de las ecuaciones hidromecánicas. Ajustando las medidas de campo a estas curvas se pueden estimar los valores del módulo de Young y el coeficiente de Poisson del acuífero y del sello. Los resultados indican que la microsismicidad inducida tiene más probabilidades de ocurrir en el acuífero que en el sello. El inicio de la microsismicidad en el sello marca la presión de inyección máxima sostenible para asegurar un almacenamiento permanente de CO2 seguro. Finalmente, analizamos la evolución termodinámica del CO2 y la respuesta termohidro- mecánica de las rocas sello y almacén a la inyección de CO2 líquido (frío). Encontramos que inyectar CO2 en estado líquido es energéticamente más eficiente porque al ser más denso que el CO2 supercrítico, requiere menor presión en cabeza de pozo para una presión dad en el acuífero. De hecho, esta presión también es menor en el almacén porque se desplaza un volumen menor de fluido. La disminución de temperatura en el entorno del pozo induce una reducción de tensiones debido a la contracción térmica del medio. Esto puede producir deslizamiento de fracturas existentes en acuíferos formados por rocas rígidas bajo contrastes de temperatura grandes, lo que podría incrementar la inyectividad de la roca almacén. Por otro lado, la estabilidad mecánica de la roca sello mejora cuando la tensión principal máxima es la vertical. Primero, investigamos numérica y analíticamente los efectos de la variabilidad de la densidad y viscosidad del CO2 en la posición de la interfaz entre la fase rica en CO2 y la salmuera de la formación. Introducimos una corrección para tener en cuenta dicha variabilidad en las soluciones analíticas actuales. Encontramos que el error producido en la posición de la interfaz al despreciar la compresibilidad del CO2 es relativamente pequeño cuando dominan las fuerzas viscosas. Sin embargo, puede ser significativo cuando dominan las fuerzas de gravedad, lo que ocurre para tiempos y/o distancias largas de inyección. Segundo, desarrollamos una solución semianalítica para la evolución de la geometría de la pluma de CO2 y la presión de fluido, teniendo en cuenta tanto la compresibilidad del CO2 como los efectos de flotación dentro del pozo. Formulamos el problema en términos de un potencial de CO2 que facilita la solución en capas horizontales, en las que hemos discretizado el acuífero. El CO2 avanza inicialmente por la porción superior del acuífero. Pero a medida que aumenta la presión de CO2, la pluma crece no solo lateralmente, sino también hacia abajo, aunque no tiene porqué llegar a ocupar todo el espesor del acuífero. Tanto la interfaz CO2-salmuera como la presión de fluido muestran una buena comparación con las simulaciones numéricas. En tercer lugar, estudiamos posibles mecanismos de rotura, que podrían llegar a producir fugas de CO2, en un sistema acuífero-sello con simetría radial, utilizando un

    Els processos termo-hidro-mecànics relacionats amb l’emmagatzematge geològic de carboni han de ser entesos i quantificats per tal de demostrar a l’opinió pública de que la injecció de diòxid de carboni (CO2) és segura. Aquesta Tesi té com a objectiu millorar aquest coneixement mitjançant el desenvolupament de mètodes per a: (1) avaluar l'evolució tant de la geometria del plomall de CO2 com de la pressió dels fluids; (2) definir un assaig de camp que permeti caracteritzar la pressió d'injecció màxima sostenible i els paràmetres hidromecànics de les roques segell i magatzem; i (3) proposar un nou concepte d'injecció que és energèticament eficient i que millora l'estabilitat de la roca segell en la majoria d’escenaris geològics a causa d'efectes termo-mecànics. Primer, investiguem numèricament i analítica els efectes de la variabilitat de la densitat i viscositat del CO2 en la posició de la interfície entre la fase rica en CO2 i la salmorra de la formació. Introduïm una correcció per tal de tenir en compte aquesta variabilitat en les solucions analítiques actuals. Trobem que l'error produït en la posició de la interfície en menysprear la compressibilitat del CO2 és relativament petit quan dominen les forces viscoses. Malgrat això, l’error pot ser significatiu quan dominen les forces de gravetat, la qual cosa té lloc per a temps i/o distàncies llargues d'injecció. Segon, desenvolupem una solució semianalítica per a l'evolució de la geometria del plomall de CO2 i la pressió de fluid, tenint en compte tant la compressibilitat del CO2 com els efectes de flotació dins del pou. Formulem el problema en termes d'un potencial de CO2 que facilita la solució en capes horitzontals, en les quals hem discretitzat l'aqüífer. El CO2 avança inicialment per la porció superior de l'aqüífer. Però a mesura que augmenta la pressió de CO2, el plomall de CO2 no només creix lateralment, sinó que també ho fa cap avall, encara que no té perquè arribar a ocupar tot el gruix de l'aqüífer. Tant la interfície CO2-salmorra com la pressió de fluid mostren una bona comparació amb les simulacions numèriques. En tercer lloc, estudiem possibles mecanismes de trencament, que podrien arribar a produir fugues de CO2, en un sistema aqüífer-segell amb simetria radial, utilitzant un model viscoplàstic. Les simulacions il·lustren que, depenent de les condicions de contorn, el moment més desfavorable té lloc a l'inici de la injecció. Tot i això, si els contorns són poc permeables, la pressió de fluid continua augmentant en tot l'aqüífer, la qual cosa podria arribar a comprometre l'estabilitat de la roca segell a llarg termini. Per a avaluar aquests problemes, proposem un assaig de caracterització hidromecànica a escala de camp per a estimar les propietats hidromecàniques de les roques segell i magatzem. Obtenim corbes per a la sobrepressió i el desplaçament vertical en funció del terme de la deformació volumètrica obtingut de l'anàlisi adimensional de les equacions hidromecàniques. Ajustant les mesures de camp a aquestes corbes es poden estimar els valors del mòdul de Young i el coeficient de Poisson de l'aqüífer i del segell. Els resultats indiquen que la microsismicitat induïda té més probabilitats d'ocórrer en l'aqüífer que en el segell. L'inici de la microsismicitat en el segell marca la pressió d'injecció màxima sostenible per tal d’assegurar un emmagatzematge permanent de CO2 segur. Finalment, analitzem l'evolució termodinàmica del CO2 i la resposta termo-hidromecànica de les roques segell i magatzem a la injecció de CO2 líquid (fred). Trobem que injectar CO2 en estat líquid és energèticament més eficient perquè al ser més dens que el CO2 supercrític, requereix una pressió menor al cap de pou per a una pressió donada a l’aqüífer. De fet, aquesta pressió també és menor a l’aqüífer perquè es desplaça un volum menor de fluid. La disminució de temperatura a l'entorn del pou indueix una reducció de tensions a causa de la contracció tèrmica del medi. Això pot produir lliscament de fractures existents en aqüífers formats per roques rígides sota contrastos de temperatura grans, la qual cosa podria incrementar la injectivitat de la roca magatzem. D’altra banda, l'estabilitat mecànica de la roca segell millora quan la tensió principal màxima és la vertical.

    Coupled thermo-hydro-mechanical (THM) effects related to geologic carbon storage should be understood and quantified in order to convince the public that carbon dioxide (CO2) injection is safe. This Thesis aims to improve such understanding by developing methods to: evaluate the CO2 plume geometry and fluid pressure evolution; define a field test to characterize the maximum sustainable injection pressure and the hydromechanical (HM) properties of the aquifer and the caprock; and propose an energy efficient injection concept that improves the caprock mechanical stability in most geological settings due to thermo-mechanical effects. First, we investigate numerically and analytically the effect of CO2 density and viscosity variability on the position of the interface between the CO2-rich phase and the formation brine. We introduce a correction to account for this variability in current analytical solutions. We find that the error in the interface position caused by neglecting CO2 compressibility is relatively small when viscous forces dominate. However, it can become significant when gravity forces dominate, which is likely to occur at late times and/or far from the injection well. Second, we develop a semianalytical solution for the CO2 plume geometry and fluid pressure evolution, accounting for CO2 compressibility and buoyancy effects in the injection well. We formulate the problem in terms of a CO2 potential that facilitates solution in horizontal layers, in which we discretize the aquifer. We find that when a prescribed CO2 mass flow rate is injected, CO2 advances initially through the top portion of the aquifer. As CO2 pressure builds up, CO2 advances not only laterally, but also vertically downwards. However, the CO2 plume does not necessarily occupy the whole thickness of the aquifer. Both CO2 plume position and fluid pressure compare well with numerical simulations. Third, we study potential failure mechanisms, which could lead to CO2 leakage, in an axysimmetric horizontal aquifercaprock system, using a viscoplastic approach. Simulations illustrate that, depending on boundary conditions, the least favorable situation may occur at the beginning of injection. However, in the presence of low-permeability boundaries, fluid pressure continues to rise in the whole aquifer, which may compromise the caprock integrity in the long-term. Next, we propose a HM characterization test to estimate the HM properties of the aquifer and caprock at the field scale. We obtain curves for overpressure and vertical displacement as a function of the volumetric strain term obtained from a dimensional analysis of the HM equations. We can then estimate the values of the Young¿s modulus and the Poisson ratio of the aquifer and the caprock by introducing field measurements in these plots. Results indicate that induced microseismicity is more likely to occur in the aquifer than in the caprock. The onset of microseismicity in the caprock can be used to define the maximum sustainable injection pressure to ensure a safe permanent CO2 storage. Finally, we analyze the thermodynamic evolution of CO2 and the THM response of the formation and the caprock to liquid (cold) CO2 injection. We find that injecting CO2 in liquid state is energetically more efficient than in supercritical state because liquid CO2 is denser than supercritical CO2. Thus, the pressure required at the wellhead is much lower for liquid than for gas or supercritical injection. In fact, the overpressure required at the aquifer is also smaller because a smaller fluid volume is displaced. The temperature decrease close to the injection well induces a stress reduction due to thermal contraction of the media. This can lead to shear slip of pre-existing fractures in the aquifer for large temperature contrasts in stiff rocks, which could enhance injectivity. In contrast, the mechanical stability of the caprock is improved in stress regimes where the maximum principal stress is the vertical.

  • Rapid drawdown and landslides

     Pinyol Puigmarti, Nuria Merce; Alonso Pérez de Agreda, Eduardo; Olivella Pastalle, Sebastian
    International Symposium on Landslides
    Presentation's date: 2012-06
    Presentation of work at congresses

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    Predicting the pore pressure distribution in a slope after rapid drawdown conditions requires the solution of a coupled flow‐deformation analysis in a saturated‐unsaturated porous media. A fully coupled finite element code (Code_Bright), able to handle in a consistent manner the drawdown conditions, is used to simulate the pore water pressure measured in the upstream slope of an earth dam (Glen Shira Dam, Scotland) subjected to a controlled rapid drawdown event. A comparison of some calculation alternatives is then given and compared with field pressure records. The paper describes also the analysis performed to interpret a recent case of a major landslide triggered by a rapid drawdown in a reservoir. A key aspect of the case is the correct characterization of permeability of representative soil profiles. This is achieved by combining laboratory test results and a back analysis of pore water pressure time records during a period of reservoir level fluctuations.

  • Modelling the FEBEX in-situ experiment including dismantling operations: incorporating the effect of additional phenomena

     Olivella Pastalle, Sebastian; Gens Sole, Antonio; Mokni, Nadia
    International Meeting on Clays in Natural and Engineered Barriers for Radioactive Waste Confinement
    Presentation's date: 2012-10
    Presentation of work at congresses

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  • Extension of CODE_BRIGHT to simulate non-isothermal CO2 injection in deep saline aquifers

     Vilarrasa Riaño, Victor; Olivella Pastalle, Sebastian; Silva Rojas, Orlando Enrique; Carrera Ramírez, Jesús
    Workshop of CODE_BRIGHT Users
    Presentation's date: 2012-05-03
    Presentation of work at congresses

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  • Joint effects of osmotic and matric suctions on hydromechanical behaviour of Boom Clay

     Mokni, Nadia; Romero Morales, Enrique Edgar; Olivella Pastalle, Sebastian
    International Meeting on Clays in Natural and Engineered Barriers for Radioactive Waste Confinement
    Presentation's date: 2012-10
    Presentation of work at congresses

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    Geomechanical stability of the caprock during CO2 sequestration in deep saline aquifers  Open access

     Vilarrasa Riaño, Victor; Olivella Pastalle, Sebastian; Carrera Ramirez, Jesus
    Energy procedia
    Date of publication: 2011
    Journal article

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    Sequestration of carbon dioxide (CO2) in deep saline aquifers has emerged as a mitigation strategy for reducing greenhouse gas emissions to the atmosphere. The large amounts of supercritical CO2 that need to be injected into deep saline aquifers may cause large fluid pressure buildup. The resulting overpressure will produce changes in the effective stress field. This will deform the rock and may promote reactivation of sealed fractures or the creation of new ones in the caprock seal, which could lead to escape paths for CO2. To understand these coupled hydromechanical phenomena, we model an axisymmetric horizontal aquifer-caprock system. We study plastic strain propagation patterns using a viscoplastic approach. Simulations illustrate that plastic strain may propagate through the whole thickness of the caprock if horizontal stress is lower than vertical stress. In contrast, plastic strain concentrates in the contact between the aquifer and the caprock if horizontal stress is larger than vertical stress. Aquifers that present a low-permeability boundary experience an additional fluid pressure increase once the pressure buildup cone reaches the outer boundary. However, fluid pressure does not evolve uniformly in the aquifer. While it increases in the low-permeability boundary, it drops in the vicinity of the injection well because of the lower viscosity of CO2. Thus, caprock stability does not get worse in semi-closed aquifers compared to open aquifers. Overall, the caprock acts as a plate that bends because of pressure buildup, producing a horizontal extension of the upper part of the caprock. This implies a vertical compression of this zone, which may produce settlements instead of uplift in low-permeability (k≤10-18 m2) caprocks at early times of injection.

  • Porosity variations in saline media induced by temperature gradients: experimental evidences and modelling

     Olivella Pastalle, Sebastian; Castagna, S.; Alonso Pérez de Agreda, Eduardo; Lloret Morancho, Antonio
    Transport in porous media
    Date of publication: 2011-12
    Journal article

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    Porosity variations in saline media containing humidity are induced by temperature gradients. A temperature imposed on a porous salt sample prepared with some brine and closed to mass transfer leads to significant variations of porosity in few weeks. Modelling of the experiments permits to understand the processes involved.

  • Deformation and flow driven by osmotic processes in porous materials: Application to Bituminised Waste Materials

     Mokni, Nadia; Olivella Pastalle, Sebastian; Valcke, Elie; Mariën, An; Smets, Esteven; Li, Xiangling
    Transport in porous media
    Date of publication: 2011-01
    Journal article

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  • Evaluation of self-combustion risk in tire derived aggregate fills

     Arroyo Alvarez de Toledo, Marcos; San Martin, Ignacio; Olivella Pastalle, Sebastian; Saaltink, Maarten Willem
    Waste management
    Date of publication: 2011-09
    Journal article

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    Lightweight tire derived aggregate (TDA) fills are a proven recycling outlet for waste tires, requiring relatively low cost waste processing and being competitively priced against other lightweight fill alternatives. However its value has been marred as several TDA fills have self-combusted during the early applications of this technique. An empirical review of these cases led to prescriptive guidelines from the ASTM aimed at avoiding this problem. This approach has been successful in avoiding further incidents of self-combustion. However, at present there remains no rational method available to quantify selfcombustion risk in TDA fills. This means that it is not clear which aspects of the ASTM guidelines are essential and which are accessory. This hinders the practical use of TDA fills despite their inherent advantages as lightweight fill. Here a quantitative approach to self-combustion risk evaluation is developed and illustrated with a parametric analysis of an embankment case. This is later particularized to model a reported field self-combustion case. The approach is based on the available experimental observations and incorporates well-tested methodological (ISO corrosion evaluation) and theoretical tools (finite element analysis of coupled heat and mass flow). The results obtained offer clear insights into the critical aspects of the problem, allowing already some meaningful recommendations for guideline revision.

  • Modelling the response of Lechago earth and rockfill dam

     Alonso Pérez de Agreda, Eduardo; Olivella Pastalle, Sebastian; Soriano, A.; Pinyol Puigmarti, Nuria Merce; Esteban, F.
    Géotechnique
    Date of publication: 2011-03
    Journal article

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    Lechago dam (Teruel, Spain) is a 40 m high zoned earth and rockfill dam sitting on soft continental deltaic deposits. A relatively narrow central clay core is stabilised by wide rockfill shoulders. The dam was well instrumented and continuous records of stress development, pore-water pressures and vertical displacements are available for the construction period. Compaction conditions were followed by means of laboratory and in situ control tests. Core clay material was investigated by means of tests performed on compacted specimens of tertiary clays. Rockfill samples were excavated in outcrops of highly fractured Cambrian quartzitic shale. A testing programme on compacted rockfill gravels was conducted under relative humidity control in a large-diameter oedometer and triaxial cells. A coupled finite-element model has been developed to analyse the tests performed and dam behaviour during construction. Model predictions, essentially based on laboratory tests, are compared with measurements during construction. The predicted response of the dam under an assumed programme of impounding is also given. In the future, once impounding occurs, it will be possible to compare these predictions with actual dam performance. The paper provides an integrated description of the dam design, construction and early behaviour. It presents a procedure to interpret available data (laboratory as well as in situ data) on compacted materials from the perspective of modern constitutive models. It also provides an evaluation of the capabilities of advanced numerical tools to reproduce the measured dam behaviour.

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    Modeling evaporation processes in a saline soil from saturation to oven dry conditions  Open access

     Gran Esforzado, Meritxell; Carrera Ramírez, Jesús; Olivella Pastalle, Sebastian; Saaltink, Maarten Willem
    Hydrology and Earth system sciences discussions
    Date of publication: 2011
    Journal article

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    Thermal, suction and osmotic gradients interact during evaporation from a salty soil. Vapor fluxes become the main water flow mechanism under very dry conditions. A coupled nonisothermal multiphase flow and a reactive transport model of a salty sand soil was developed to study such an intricate system. The model was calibrated with data from an evaporation experiment (volumetric water content, temperature and concentration). The retention curve and relative permeability functions were modified to simulate oven dry conditions. Experimental observations were satisfactorily reproduced, which suggests that the model can be used to assess the underlying processes. Results show that evaporation is controlled by heat, and limited by salinity and liquid and vapor fluxes. Below evaporation front vapor flows downwards controlled by temperature gradient and thus generates a dilution. Vapor diffusion and dilution are strongly influenced by heat boundary conditions. Gas diffusion plays a major role in the magnitude of vapor fluxes.

  • Dynamics of water vapor flux and water separation processes during evaporation from a salty dry soil

     GRAN, MERITXELL; MASSANA, JORDI; Carrera Ramírez, Jesús; Saaltink, Maarten Willem; Olivella Pastalle, Sebastian; Ayora Ibáñez, Carlos; Lloret Morancho, Antonio
    Journal of hydrology
    Date of publication: 2011-01
    Journal article

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    Evaporation from a salty soil generates salt accumulation near the surface with the subsequent deterioration of the soil quality. Salinization mechanisms are poorly understood despite their global impact. Vapor flux and solute transport were studied under evaporation conditions. Laboratory experiments consisted of open sand and silt columns initially saturated with epsomite (MgSO47H2O) or halite (NaCl) solutions. Salt precipitation occurred only above the evaporation front, which occupied a very narrow region. Vapor flowed both upwards and downwards from this front. The downward vapor flow condensed further down the column, diluting the solution. This gave rise to two areas: a high salinity area above the evaporation front, and a diluted solution area below it. The effects of thermal, suction and osmotic gradients on water fluxes were studied in order to better understand the underlying mechanisms of this phenomenon.

    Evaporation from a salty soil generates salt accumulation near the surface with the subsequent deterioration of the soil quality. Salinization mechanisms are poorly understood despite their global impact. Vapor flux and solute transport were studied under evaporation conditions. Laboratory experiments consisted of open sand and silt columns initially saturated with epsomite (MgSO4 7H2O) or halite (NaCl) solutions. Salt precipitation occurred only above the evaporation front, which occupied a very narrow region. Vapor flowed both upwards and downwards from this front. The downward vapor flow condensed further down the column, diluting the solution. This gave rise to two areas: a high salinity area above the evaporation front, and a diluted solution area below it. The effects of thermal, suction and osmotic gradients on water fluxes were studied in order to better understand the underlying mechanisms of this phenomenon.

  • Thermo-hydro-mechanical model of the Canister Retrieval Test

     Zandarín Iragorre, Maria Teresa; Gens Sole, Antonio; Olivella Pastalle, Sebastian; Alonso Pérez de Agreda, Eduardo
    Physics and chemistry of the Earth
    Date of publication: 2011
    Journal article

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  • A bridge foundation analysis

     Puig Damians, Ivan; Olivella Pastalle, Sebastian; Josa Garcia-tornel, Alejandro
    Date: 2011-06-02
    Report

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  • Is the degree of saturation a good candidate for Bishop¿s X parameter?

     Pereira, J.M.; Coussy, Olivier; Alonso Pérez de Agreda, Eduardo; Vaunat, Jean; Olivella Pastalle, Sebastian
    International Conference on Unsaturated Soils
    Presentation's date: 2011
    Presentation of work at congresses

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    In unsaturated soil mechanics, the quest for an effective stress playing the same role as Terzaghi’s effective stress does for saturated soils has introduced a long standing debate, dating back to the 1960s. Several contributions have been proposed since the early work of Bishop. It is well recognized to date that a single constitutive stress is not sufficient by itself to catch the main features of the behaviour of unsaturated soils and it is often combined with matric suction. In this paper, focus is given to a largely used formulation for such a constitutive stress, based on the use of an averaged pore pressure. In particular, this paper discusses on thermodynamics bases the validity of the choice of the factor X weighting the fluid pressures contribution to the constitutive stress. This factor is usually assumed to be equal to the degree of saturation of water. In this work it is shown that the choice of this natural candidate implies restrictive assumptions on the plastic flow rule. As shown from experimental data obtained from a literature review, this choice may not be pertinent for certain classes of materials, particularly high plasticity clays.

  • Deformation and flow driven by osmotic processes in porous materials  Open access  awarded activity

     Mokni, Nadia
    Defense's date: 2011-02-22
    Department of Geotechnical Engineering and Geo-Sciences, Universitat Politècnica de Catalunya
    Theses

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    En el caso del almacenamiento de los residuos radioactivos los flujos osmóticos pueden ser relevantes y requieren un análisis en detalle. El residuo nuclear bituminizado (BW) será almacenado mediante contenedores en cavidades excavadas en la Boom Clay, que es una arcilla marina que presenta propiedades favorables para limitar y retrasar la migración de los contaminantes radioactivos. La interacción entre los dos materiales es un proceso acoplado químico-hidro-mecánico y depende de la respuesta hidromecánica de la Boom Clay y del BW. En condiciones de almacenamiento, el contacto del BW, que contienen cantidades importantes de NaNO3, con el agua subterránea induce la hidratación por gradientes osmóticos y el consiguiente hinchamiento, además de la difusión de la sal disuelta hacia la Boom Clay. Se pueden distinguir dos tipos de afecciones: la perturbación geomecánica causada por el hinchamiento del BW y el aumento de presión en el BW y cambio de las distribución de tensiones en la roca, y la perturbación físico química por la migración de grandes cantidades de sales. El objetivo de esta tesis es: (i) Mejorar la comprensión de los procesos que controlan la absorción de agua y el consecuente hinchamiento del BW que contengan sales (NaNO3), y (ii) Investigar los posibles efectos de la concentración de fluidos de los poros sobre el hinchamiento, la compresibilidad y comportamiento de corte de la Boom Clay. En primer lugar, se ha desarrollado una formulación para el análisis de la deformación inducida por la disolución de sales en medio poroso con contacto con agua. Las ecuaciones planteadas incluyen los flujos acoplados de agua y soluto. Se presenta también un trabajo teórico que ayuda a la comprensión del comportamiento mecánico del BW. Se considera este material como una mezcla de bitumen y cristales de NaNO3. Se ha desarrollado un modelo elasto-viscoplástico que describe el comportamiento de fluencia del BW considerando el comportamiento de fluencia de sus constituyentes. El modelo constitutivo elasto-viscoplástico ha sido implementado en el programa CODE_BRIGHT. Los resultados se han comparado con observaciones experimentales. Se ha estudiado el comportamiento a largo plazo del BW en contacto con agua al simular ensayos de hinchamiento por absorción de agua bajo condiciones confinadas. El análisis numérico ha demostrado ser capaz de proporcionar una representación satisfactoria de los principales patrones observados en su comportamiento. En lo que respecta al segundo objetivo de la tesis, se ha propuesto una formulación para el análisis de las deformaciones inducidas por procesos osmóticos en un medio poroso de doble estructura. Esta formulación distingue dentro del material un nivel micro-estructural y otro macro-estructural con cambios químicos que tienen un efecto significativo en la micro-estructura. Se han obtenido las ecuaciones básicas que describen los flujos acoplados de agua y solutos y el transporte de sus componentes a través de los macroporos así como las ecuaciones de balance de masa para agua y soluto en los macroporos y microporos. La formulación propuesta ha sido aplicada particularmente para analizar cualitativamente el efecto de la succión osmótica sobre el hinchamiento de los suelos arcillosos. Se han analizado los efectos a corto y largo plazo. Se ha investigado también la influencia del aumento de la concentración del fluido en los poros sobre las propiedades geotécnicas y el comportamiento de la Boom Clay no saturada. Se ha llevado a cabo un programa sistemático de investigación experimental, con control de succión osmótica y matricial, con el fin de investigar el efecto del incremento de la concentración del fluido de poros sobre la resistencia de corte y el cambio volumétrico bajo condiciones edométricas. Se ha observado, que bajo condiciones parcialmente saturadas, un cambio en la salinidad provoca una disminución en la compresibilidad y en la resistencia de corte del material.

    For deep storage of high-level nuclear waste osmotic flows can be significant and so require a careful analysis. In Belgium, The bituminized nuclear waste (BW) named Eurobitum contained in metallic drums will be placed inside a tunnel or a shaft excavated in the Boom Clay, which is 100 m thick marine clay presenting favourable properties to limit and delay the migration of the leached radionuclides over extended periods of time. In Geological disposal conditions, contact of the bituminized radioactive waste which contains high amounts of highly soluble salt (NaNO3) with groundwater will result in water uptake and swelling of the waste and in subsequent diffusion of the dissolved salt through the host clay formation. Basically, two types of disturbance can be distinguished: A geo-mechanical perturbation, caused by the swelling of the waste and the increase of the pressure in and around the waste and a physico-chemical perturbation by the release of large amounts of NaNO3 and other soluble salts. In this context the aim of this thesis is: (i) to improve the understanding of the processes controlling the water uptake and the subsequent swelling of bituminized waste containing soluble salts (NaNO3), and (ii) to investigate of the possible effects of the increase of pore fluid concentration on swelling, compressibility and shear behaviour of Boom Clay. A formulation has been proposed for the analysis of deformation induced by dissolution of salts in porous media in contact with water. The equations include the effect of coupled transport phenomena and the formulation has been included as an extension in the coupled THM program CODE_BRIGHT. A theoretical and experimental work aiming at understanding the mechanical behaviour of the Bituminized Waste has been presented.This material is considered for this purpose as a mixture of bitumen and crystals of NaNO3. An elasto-viscoplastic model has been developed that describes the creep behaviour of BW considering the constituents' creep behaviour. The elasto-viscoplastic constitutive model has been implemented into CODE_BRIGHT. The modelling results have been compared with the experimental data. The impact of osmotic forces on the swelling of the material has been investigated by simulating water uptake swelling tests under confined conditions and comparing the predictions with experimental results. The numerical analysis has proven to be able to furnish a satisfactory representation of the main observed patterns of the behaviour. In regard to the second objective of this thesis, a formulation has been proposed for the analysis of deformations induced by osmotic processes in double structure porous media. The formulation is based on the distinction within the material of a microstructural and a macrostructural levels with chemical changes having a significant effect on the microstructure. A macroscopic description of the system is provided. Then the basic equations describing coupled flows of water and solutes and the transport of its components through macropores and mass balance equations for water and solute in macro and micro pores have been obtained. The proposed formulation has been particularly applied to analyze qualitatively the effect of osmotic suction on swelling of clayey soils. Transient and long term effects have been analyzed. The influence of pore fluid concentration on the geotechnical properties and behavior of Boom Clay under partially saturated conditions has been investigated. A systematic experimental research program involving osmotic suction and matric suction controlled experiments has been carried to investigate the effect of the increase of pore fluid concentration on shear strength and on the volume change behaviour under odometer stress state conditions. It has been observed that under partially saturated conditions a change in salinity causes a decrease in compressibility and shear strength.

  • A study of the effects of suction and roughness on the mechanical behaviour of rock joints

     Zandarín Iragorre, Maria Teresa; Alonso Pérez de Agreda, Eduardo; Olivella Pastalle, Sebastian
    International Symposium on Computational Geomechanics
    Presentation's date: 2011-04
    Presentation of work at congresses

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    The experimental investigation focused on the effects of suction on the mechanical behaviour of rock joints. Available experimental data on the effect of moisture on joint behaviour is very scarce. Laboratory tests were performed in a direct shear cell equipped with suction control. Suction was imposed using a vapour forced convection circuit connected to the cell and controlled by an air pump. Artificial joints of Lilla claystone were prepared. Joint roughness of varying intensity was created by carving the surfaces in contact in such a manner that rock ridges of different tip angles were formed. Several tests were performed for different values of suction (20, 100 and 200 MPa) and for different values of vertical stress (30, 60 and 150 kPa). A constitutive model including the effects of suction and joints roughness is proposed to simulate the unsaturated behaviour of rock joints. The new constitutive law was incorporated into the FE computer code Code-Bright and experimental results were numerically simulated.

  • Coupled THMC analysis in porous media

     Gens Sole, Antonio; Guimarães, Leonardo do N; Olivella Pastalle, Sebastian
    Symposium on Mechanics and Physics of Porous Solids
    Presentation's date: 2011-04
    Presentation of work at congresses

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    A coupled thermo-hydro-mechanical-chemical (THMC) formulation is presented. The formulation combines a THM approach already existing and operational with the equations of reactive transport in a fully coupled manner. The reactive transport equations are set in the context of an unsaturated deformable porous medium with several chemical species dissolved in the liquid phase but also present in the solid phase. Chemical reactions considered in the formulation include: i) homogeneous reactions: aqueous complex formation, acid/base and oxidationlreduction, and ii) heterogeneous reactions: dissolution/precipitation of minerals and cation exchange. Local equilibrium is assumed for all the chemical reactions except for dissolutionlprecipitation of minerals where kinetics can also be considered. Two examples of application are described. The fust one addresses the issue of scale formation around boreholes when oil production is stimulated by waterflooding. In the second one, the THMC behaviour of a bentonite engineered barrier is analyzed in the context of a large scale in situ heating test.

  • Hydromechanical behaviour of the aquifer and caprock under high pressure injection

     Vilarrasa Riaño, Victor; Olivella Pastalle, Sebastian; Carrera Ramírez, Jesús
    Trondheim CCS Conference
    Presentation's date: 2011
    Presentation of work at congresses

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    CO2 injection in deep saline sloping aquifers through a vertical well  Open access

     Vilarrasa Riaño, Victor; Olivella Pastalle, Sebastian; Carrera Ramirez, Jesus
    Workshop of CODE-BRIGHT Users
    Presentation's date: 2011
    Presentation of work at congresses

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  • Coupled hydromechanical processes during CO2 sequestration in deep saline aquifers

     Vilarrasa Riaño, Victor; Olivella Pastalle, Sebastian; Carrera Ramirez, Jesus
    International Conference on Computational Methods for Coupled Problems in Science and Engineering
    Presentation's date: 2011-06-20
    Presentation of work at congresses

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  • Hydromechanical characterization test for CO2 sequestration in deep saline aquifers

     Vilarrasa Riaño, Victor; Olivella Pastalle, Sebastian; Carrera Ramírez, Jesús
    European Geosciences Union General Assembly
    Presentation's date: 2011-04-03
    Presentation of work at congresses

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  • Lechago dam: a case study

     Alonso Pérez de Agreda, Eduardo; Olivella Pastalle, Sebastian; Pinyol Puigmarti, Nuria Merce
    Laboratório Nacional de Engenharia Civil - International Conference on Dam Engineering
    Presentation's date: 2011
    Presentation of work at congresses

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    Lechago dam (Teruel, Spain) is a 40 m high zoned earth and rockfill dam founded on soft continental deltaic deposits. A relatively narrow central clay core is stabilized by wide rockfill shoulders. The dam was completed in January 2009 and impounding will probably start at the beginning of 2011. The dam was well instrumented and continuous records of stress development, pore water pressures and horizontal and vertical displacements are available for the construction period. The clay core material was investigated by means of tests performed on compacted specimens of Tertiary clays. Rockfill samples were excavated in outcrops of highly fractured Cambrian quartzitic shale. In the years to follow the dam design, an extensive testing program on compacted rockfill gravels was conducted under Relative Humidity control in large diameter oedometer and triaxial cells. The results of this research have been reported in a number of papers. A coupled FE model has been developed to analyze the dam behaviour during construction. Model predictions, essentially based on laboratory tests, are compared with measurements during construction.

  • Deformation of bitumen based porous material: experimental and numerical analysis

     Mokni, Nadia; Olivella Pastalle, Sebastian; Li, Xiangling; Smets, Esteven; Valcke, Elie; Mariën, An
    Journal of nuclear materials
    Date of publication: 2010-09
    Journal article

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  • Osmosis-induced swelling of Eurobitum bituminized radioactive waste in constant total stress conditions

     Valcke, Elie; Mariën, An; Smets, Esteven; Mokni, Nadia; Olivella Pastalle, Sebastian; Sillen, X.
    Journal of nuclear materials
    Date of publication: 2010-11
    Journal article

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    Some investigations about the tensile strength and the desiccation process of unsaturated clay  Open access

     Trabelsi, H; Jamei, M.; Guiras, H.; Hatem, H; Romero Morales, Enrique Edgar; Olivella Pastalle, Sebastian
    European physical journal. Special topics
    Date of publication: 2010-06-10
    Journal article

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    The current paper presents an investigation on the tensile strength of unsaturated clay, and a discussion about the significant differences between the behaviours of compacted soils and those of the completely remoulded soils. The adapted experimental device based on the shear box for the measurement of the tensile strength is also presented. In the tensile tests, stress-strain characteristics are measured using high precision transducers and electronic data acquisition. The equipment is capable of measuring tensile strengths of soil (about 10 MPa). Moreover, a new model to predict cracks is presented in 3D. This analytical model for the prediction of tensile strength, as a function of suction and porosity, is given.

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    Effect of thermo-coupled processes on the behaviour of a clay barrier submitted to heating and hydration  Open access

     Sánchez, M.; Gens Sole, Antonio; Olivella Pastalle, Sebastian
    Anais da Academia Brasileira de Ciências
    Date of publication: 2010
    Journal article

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

  • Effects of CO2 Compressibility on CO2 Storage in Deep Saline Aquifers

     Vilarrasa, Víctor; Bolster, Diogo; Dentz, Marco; Olivella Pastalle, Sebastian; Carrera Ramirez, Jesus
    Transport in porous media
    Date of publication: 2010
    Journal article

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  • A microstructurally based effective stress for unsaturated soils

     Alonso Pérez de Agreda, Eduardo; Pereira, J.M.; Vaunat, Jean; Olivella Pastalle, Sebastian
    Géotechnique
    Date of publication: 2010-06
    Journal article

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