A modelling procedure to address the tunnel–anhydritic rock interaction is described in this paper. The model incorporates the basic physico-chemical phenomena involved in rock swelling, often observed during excavation and subsequent operation of tunnels. It includes (a) a provision for rock damage during tunnel excavation, (b) the precipitation of gypsum crystals in discontinuities and (c) a stress-dependent relationship between swelling strains and mass of gypsum precipitation. The model includes hydro-mechanical coupling and the transport of sulfate salts dissolved in the massif water. Rock damage is described by the development of a network of fractures that increases permeability and allows gypsum crystal growth. Field information, laboratory data and monitoring records available for Lilla tunnel, located in the province of Tarragona, Spain and excavated in Tertiary anhydritic claystone, were selected as a convenient benchmark case to test model capabilities. Predictions and measurements (swelling records of the unlined tunnel floor and swelling pressures against a structural invert) were found to agree reasonably well.
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Las expansiones ocurridas en el túnel de Lilla son el resultado del crecimiento de cristales de yeso en discontinuidades. Se describe un procedimiento de análisis numérico para el diseño de un túnel en roca anhidrítica expansiva. El modelo incorpora un acoplamiento hidro-mecánico y el transporte de sales disueltas en el agua intersticial e incluye el daño generado en la roca tras la excavación del túnel, la precipitación de cristales en discontinuidades y la dependencia entre las deformaciones de hinchamiento y la masa precipitada de yeso. La respuesta del modelo es coherente con las medidas de campo disponibles.
Sánchez, M.; Gens, A.; Victoria, M.; Olivella, S. International journal of geomechanics Vol. 16, num. 6, p. D4016015-1-D4016015-17 DOI: 10.1061/(ASCE)GM.1943-5622.0000728 Data de publicació: 2016-12 Article en revista
This work presents a fully coupled formulation developed to handle engineering problems in unsaturated (and saturated) soils that present two dominant void levels. The proposed framework assumes the presence of two porous media linked through a mass-transfer term between them. In its more general form, the proposed approach allows the consideration of nonisothermal multiphase flow coupled with the mechanical problem. The double-porosity formulation was implemented in a finite-element code and has been used to analyze a variety of engineering problems. The approach is especially suitable for cases in which the material exhibits a strong coupling between the mechanical and the hydraulic problems in both media, such as with swelling clays. For those types of problems, the proposed formulation is used in conjunction with the mechanical double-structure model already proposed by the authors. This paper presents the coupled formulation and the application of the proposed approach to problems involving expansive unsaturated clays. Very satisfactory results were obtained in these analyses. -
This paper describes the thermohydromechanical (THM) simulation of engineered barrier systems (EBS) for the final disposal of nuclear spent fuel in Finland. The bentonite barriers were simulated with the Barcelona Basic Model and the model was calibrated from laboratory tests. The evolution of gap closure and the presence of a fracture intersecting the disposal were analysed. The simulations were performed in 2D axisymmetrical geometries. Full 3D simulations were carried out in order to check the effect of the third dimension. The time required for the barriers to reach full saturation, the maximum temperature, deformations and displacements at the buffer–backfill interface and the homogenization of components both locally and globally are the main interests. The effect of rock fracture and the hydraulic conductivity of the rock are subjected to 2D sensitivity analyses.
The use of artificial ground freezing (AGF) to form earth support systems has had applications worldwide. These cover a variety of construction problems, including the formation of frozen earth walls to support deep excavations, structural underpinning for foundation improvement and temporary control of ground water in construction processes. On one hand, the main advantage of AGF as a temporary support system in comparison to other support methods, such as those based on injections of chemical or cement grout into the soil, is the low impact on the surrounding environment as the refrigerating medium required to obtain AGF is circulated in pipes and exhausted in the atmosphere or re-circulated without contamination of the ground water. On the other hand, the available methods may vary significantly in their sustainability and complexity in terms of times and costs required for their installation and maintenance. The ability to predict the effects induced by AGF on granular materials is therefore crucial to assessing construction time and cost and to optimising the method. In this work, the thermo-hydro-mechanical processes induced by artificial freezing of a soil body are studied using a constitutive model that encompasses frozen and unfrozen behaviour within a unified effective-stress-based framework. It makes use of a combination of ice pressure, liquid water pressure and total stress as state variables. The model is validated and calibrated using the results of a series of laboratory tests on natural samples of a volcanic ash (Pozzolana) retrieved during construction of Napoli underground, where the technique of AGF was used extensively to stabilise temporarily the ground and control the ground water.
Jamei, M.; Guiras, H.; Olivella, S. European journal of environmental and civil engineering Vol. 19, num. 9, p. 1033-1058 DOI: 10.1080/19648189.2014.996670 Data de publicació: 2015-10 Article en revista
In some arid and semi-arid regions, different types of infrastructure assets suffer from degradation of the roads, the embankment failures, erosion due to cyclic hydraulic actions and the effects of rainfall infiltration on slopes. Typical cases, such as the national roads in the north-west of Tunisia (Beja city) have been affected dramatically. Recent landslide is manifested in this region, especially in a plastic clay soil. Stability problems are caused by soil saturation and the presence of abundant cracks which are developed after a long dry summer. In fact, due to geotechnical problems, the annual loss due to the damage is estimated at $1 million in Beja area (30 km(2)). The effect of rainfall infiltration into the unsaturated clay during wet seasons characterised by either long duration low intensity rain or short duration high intensity rain have been analysed. The elastoplastic Barcelona Basic Model (BBM) has been used and soil movements leading to slope failure were calculated according to the unsaturated state evolution. The effects of cyclic hydraulic paths on the yield function have also been investigated. The yield function evolution depends on the cohesion and the apparent consolidation stress variations. The numerical calculations were evaluated against the field measurement displacements.
The HG-A in situ test, located at the Mont Terri Underground Rock Laboratory (URL), was analysed as part of the FORGE project. This test investigated the behaviour of the excavation damage zone (EDZ) around a backfilled microtunnel by a series of water- and gas-injection tests. Prior to testing, the backfilled microtunnel was sealed with a hydraulic megapacker system. A key aspect was the investigation of crack opening and closure along the EDZ in response to water and gas injections in the context of radioactive waste disposal. In the model, the intrinsic permeability of the EDZ was assumed to depend on deformation, and additional simplifying assumptions were considered: axisymmetry about the tunnel axis; no gravity; soil slices orthogonal to the tunnel axis move independently and in plane strain; liquid and gas flows along the EDZ parallel to the tunnel axis; and undrained saturated conditions for the Opalinus Clay. As a result, the field equations were reduced to differential equations for liquid and gas pressures defined in a one-dimensional (1D) domain representing the EDZ. The main trends of the pressure evolution observed in the test section were reproduced. A 2D axisymmetric model confirmed the validity of the simplifying assumptions, except for small zones of the EDZ near the megapacker ends.
An experimental programme involving osmotic and matric suction controlled tests is carried out to investigate the effects of increasing pore fluid concentration, chemical cycling (salinisation/dilution) and matric suction on the liquid retention properties, shear strength and volume change behaviour of Boom Clay. This Tertiary Clay formation has been thoroughly investigated as a possible host material for the disposal of Eurobitum bituminised radioactive waste (BW) in Belgium. Within this context chemical impact and partially saturated conditions are studied in a combined way to cover a wide range of in-situ states induced by underground construction, ventilation and diffusion of a large amount of sodium nitrate (NaNO3) (contained in the bituminised waste). Statically compacted specimens are prepared at different sodium nitrate concentrations or are exposed, at constant vertical stress, to sodium nitrate salinisation or pore water dilution. An aggregated structure with a double porosity network is induced on salinisation and subsequent compaction even at high water contents. An increase in pore fluid concentration enhances the aggregation of the microstructure and reduces the liquid retention properties of the material. Results of oedometer tests performed under constant matric suction and increasing osmotic suction show shrinkage of the sample, a decrease of the compressibility and an increase in the preconsolidation stress. Shear strength results have been interpreted using a single constitutive stress (average skeleton stress) to take into account matric suction and chemical effects on degree of saturation and on microstructural changes. A unique linear shear strength failure envelope has been obtained for the tests performed at different osmotic and matric suctions. The modification of the liquid retention behaviour of the material induced by salinisation has proven to be a crucial aspect for the interpretation of the obtained results.
The hydro-chemical (CH) interaction between swelling Eurobitum bituminized radioactive waste (BW) and Boom Clay was investigated to assess the feasibility of geological disposal for the long-term management of this waste. First, the long-term behaviour of BW in contact with water was studied. A CH formulation of chemically and hydraulically coupled flow processes in porous materials containing salt crystals is discussed. The formulation incorporates the strong dependence of the osmotic efficiency of the bitumen membrane on porosity and assumes the existence of high salt concentration gradients that are maintained for a long time and that influence the density and motion of the fluid. The impacts of temporal and spatial variations of key transport parameters (i.e. osmotic efficiency (s), intrinsic permeability (k), diffusion, etc.) were investigated. Porosity was considered the basic variable. For BW porosity varies in time because of the water uptake and subsequent processes (i.e. dissolution of salt crystals, swelling of hydrating layers, compression of highly leached layers). New expressions of s and k describing the dependence of these parameters on porosity are proposed. Several cases were analysed. The numerical analysis was proven to be able to furnish a satisfactory representation of the main observed patterns of the behaviour in terms of osmotic-induced swelling, leached mass of NaNO3 and progression of the hydration front when heterogeneous porosity and crystal distributions have been assumed. Second, the long-term behaviour of real Eurobitum drums in disposal conditions, and in particular its interaction with the surrounding clay, was investigated. Results of a CH analysis are presented.
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.
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.
Arnedo, D.; Alonso, E.; Olivella, S. International journal for numerical and analytical methods in geomechanics Vol. 37, num. 14, p. 2239-2256 DOI: 10.1002/nag.2132 Data de publicació: 2013-10 Article en revista
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.
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.
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.
Nishimura, S.; Jardine, R.; Fenton, C.; Olivella, S.; Gens, A.; Martin, C. International Conference on Soil Mechanics and Geotechnical Engineering p. 3391-3394 Data de presentació: 2013-09 Presentació treball a congrés
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.
Casini, F.; Gens, A.; Olivella, S.; Viggiani, G.M.B. International Symposium on Coupled Phenomena in Environmental Geotechnics p. 467-473 DOI: 10.1201/b15004-61 Data de presentació: 2013-07 Presentació treball a congrés
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.
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.
Zandarín, M.T.; Alonso, E.; Olivella, S. International journal of rock mechanics and mining sciences Vol. 60, p. 333-344 DOI: 10.1016/j.ijrmms.2012.12.007 Data de publicació: 2013-06 Article en revista
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...
Gens, A.; Nishimura, S.; Casini, F.; Olivella, S.; Jardine, R. International Conference on Computational Methods for Coupled Problems in Science and Engineering p. 579 Data de presentació: 2013-06 Presentació treball a congrés
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.
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.
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...
Olivella, S.; Gens, A.; Mokni, N. International Meeting on Clays in Natural and Engineered Barriers for Radioactive Waste Confinement p. 633-634 Data de presentació: 2012-10 Presentació treball a congrés
Mokni, N.; Romero, E.; Olivella, S. International Meeting on Clays in Natural and Engineered Barriers for Radioactive Waste Confinement p. 162-163 Data de presentació: 2012-10 Presentació treball a congrés
Trabelsi, H.; Jamei, M.; Zenzri, H.; Olivella, S. International journal for numerical and analytical methods in geomechanics Vol. 36, num. 11, p. 1410-1433 DOI: 10.1002/nag.1060 Data de publicació: 2012-08-10 Article en revista
Premi extraordinari doctorat curs 2011-2012, àmbit d’Enginyeria Civil
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
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
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.
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.
Sánchez, M.; Gens, A.; Olivella, S. International journal for numerical and analytical methods in geomechanics Vol. 36, num. 4, p. 391-421 DOI: 10.1002/nag.1011 Data de publicació: 2012-03 Article en revista
'The project focuses on the theoretical and applied study of freezing soils in the context of the use of Artificial Ground Freezing (AGF) in excavations and underground construction. The ever-increasing density of urban environments poses new challenges to tunnelling for transit projects. This implies the necessity to carry out open excavations and bored tunnels in the urban environment, often in difficult ground and almost always in the close vicinity of existing buildings and structures. As a test case, the project examines the geotechnical aspects of excavation of Line 1 of Napoli Underground. The work was performed in the urban environment of one of the most densely populated cities in Europe. Monitoring included an extensive set of in-situ data (e.g. buildings displacements, temperature in the ground).
The main objectives of the project are: a deeper understanding of the AGF process and of the effects of thawing frozen ground; development of a novel constitutive model and coupled thermo-hydro-mechanical (THM) formulation to provide an accurate description of the engineering behaviour of frozen/unfrozen soils; comparison between laboratory and field tests to calibrate the thermal properties of the ground, collection and back analysis of an extensive set of in-situ monitored data from a real urban tunnelling project. The most innovative aspect of the project is the way in which theoretical developments, constitutive modelling, laboratory tests, in situ monitoring and coupled analysis will be integrated in a single consistent framework firmly grounded on basic physical principles. The generality of the formulation and of the developed analysis tool allows the enhancement of the field of applications from AGF to the wider range of engineering and environmental problems involving frozen soils such as the analysis of frost heave, the study of the effect of freezing-thawing cycles in cold regions or the prediction of the permafrost fate in a climate change scenario.'
Two real cases: the potential effect of an induced infiltration in the vicinity of an
embankment founded on potentially collapsible natural silts and the effect of rainfall regime on a canal founded on cemented collapsible silts are discussed. Tests performed to determine the parameters of an elastoplastic constitutive model (BBM) for the unsaturated foundation materials are described. Hydraulic properties were also determined. The two cases are simulated through the computer program CODE_BRIGHT. The calculation scenarios aim at studying limiting cases, to establish the risk of embankment malfunctioning.
The calculation of pore water pressure distribution in a slope partially submerged and subjected to a drawdown is analyzed in this chapter. Drawdown phenomenon is a critical situation for the stability of slopes of earth dams and bank rivers affected by variations of water level. The prediction of pore water pressure in two earth dams subjected to a drawdown event under different calculation hypothesis highlight that classical flow methods of analysis may overestimate or underestimate pore water pressures depending on several external condition and material properties. In particular, an instrumented dam is simulated and calculated results can be compared with field measurements. Finally, in the chapter, an incipient landslide (40 Mm3) in the left margin of a reservoir triggered by a drawdown is presented and
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.
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.
This document presents the analysis with CODE_BRIGHT finite element program of a geotechnical case. The problem analyzed is related to a mechanical analysis of soilstructure interaction considering different alternatives for the foundation of a bridge in El Prat de Llobregat (Highway A-2). The comparison of displacements shows that an alternative solution using shallow foundations can be considered in addition to the originally proposed, composed by sheet walls.
This document presents the analysis with CODE_BRIGHT finite element program
of a geotechnical case. The problem analyzed is related to a mechanical analysis of soilstructure
interaction considering different alternatives for the foundation of a bridge in El
Prat de Llobregat (Highway A-2). The comparison of displacements shows that an alternative
solution using shallow foundations can be considered in addition to the originally proposed,
composed by sheet walls.
Vilarrasa, V.; Olivella, S.; Carrera, J. International Conference on Computational Methods for Coupled Problems in Science and Engineering p. 1 Data de presentació: 2011-06-20 Presentació treball a congrés
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.
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.
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.
Premi extraordinari doctorat curs 2010-2011, àmbit d’Enginyeria Civil
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.
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.
Gran, M.; MASSANA, J.; Carrera, J.; Saaltink, M.; Olivella, S.; Ayora, C.; Lloret, A. Journal of hydrology Vol. 396, num. 3-4, p. 215-220 DOI: 10.1016/j.jhydrol.2010.11.011 Data de publicació: 2011-01 Article en revista
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.