To ensure secure geological storage of carbon dioxide it is necessary to establish the integrity of the overlying sealing rock. Seal rock fractures are key potential leakage pathways for storage systems; understanding their behaviour in the presence of CO2 under reservoir conditions is therefore of great importance. This thesis presents experimental investigations into the hydraulic behaviour of discrete fractures within low permeability seal rocks during single phase supercritical CO2 flow, under varying mechanical and thermal conditions representative of in-situ conditions. An experimental rig was designed and built to enable the controlled study of supercritical CO2 flow through 38 mm diameter samples under high pressures and temperatures. Samples are placed within a Hassler-type uniaxial pressure cell and CO2 flow is controlled via high precision syringe pumps. Flow experiments with supercritical CO2 within the pressure range 10-50 MPa were undertaken at temperatures of 38°C and 58°C with confining pressures of 35-55 MPa. The effects of stress loading and temperature change on the hydraulic properties of the fractured sample were studied; continuous differential pressure measurement enabled analysis of hydraulic response. Experiments were undertaken on a pre-existing Wissey field Zechstein Dolomite fracture and three artificial fractures (two East Brae field Kimmeridge Clay samples and one Cambrian shale quarry sample). Fracture permeabilities ranged from 8 X 10-14 m2 to 6 X 10-11 m2 with higher permeabilities observed within the harder rock samples. A broadly linear flow regime, consistent with Darcy's law, was observed in the lowest permeability sample (East Brae). A Forchheimer-type non-linear flow regime was observed in the other samples. Transmissivity variations during experiments were used to infer the mechanical impact of stress and temperature changes. An increase in effective stress resulted in transmissivity reduction, suggesting fracture aperture closure. During initial stress loading cycles, and subsequent higher temperature stress loading, a component of this transmissivity reduction was found to be inelastic, suggesting permanent modification of fracture geometry during closure. Pre- and post-experiment fracture surface characterisation provides further evidence for the occurrence of plastic deformation. Transmissivity-stress relationships were elastic during subsequent external stress-loading cycles, suggesting elastic closure and opening of fractures without additional permanent fracture geometry changes. The impact of fluid property variations on fracture hydraulic conductivity, Kfrac, was also analysed. Under constant effective stress Kfrac was found to be higher within high temperature and low fluid pressure scenarios, due to higher density/viscosity ratios. However, under constant confining pressure, fluid pressure changes are coupled both to mechanical effects (from effective stress alteration) and hydraulic effects (from viscosity variation), with opposing impacts on fracture hydraulic conductivity. At lower effective stresses mechanical effects were found to be dominant, with fluid pressure increase resulting in a notable increase to Kfrac due to aperture opening. At higher effective stresses, mechanical changes are much smaller due to increased contact area between fracture surfaces, and thus increased stiffness of fractures. Under such conditions hydraulic effects may be dominant and result in a small Kfrac reduction as fluid pressure increases, due to a reduction in the density/viscosity ratio. These results highlight that CO2 fluid property variation can have a notable influence on hydraulic conductivity under certain in-situ conditions. The single phase CO2 fracture flow experiments undertaken during this study were designed to enable a study of hydraulic and mechanical processes in isolation, without the influence of chemical processes. In-situ, the additional presence of brine and thus multiphase fluid behaviour and associated chemical processes makes the hydraulic behaviour of fractures considerably more complex. Coupled process modelling enables the relative influence of these processes to be simulated, but relies on experiments for validation. These unique experimental findings are of great value for enabling validation of such models as well as for informing analyses of geological and field studies.

Vegetation stabilises slopes via both mechanical reinforcement (through root anchorage) and hydrologic reinforcement (through transpiration-induced soil matric suction). However, relatively little is known about the effectiveness of different plant species in stabilising soil slopes via the two reinforcing mechanisms, and so decisions on species selection are seldom made with optimisation of slope reinforcement in mind. In this thesis, a comprehensive testing programme including laboratory, glasshouse and field experiments is designed and implemented, with the aim to quantify and investigate the transpiration-induced hydrologic reinforcement and root biomechanical properties during the early plant establishment of selected woody species, widespread under European temperate climate. Ten species native to Europe (Buxus sempervirens L.; Corylus avellana L.; Crataegus monogyna Jacq.; Cytisus scoparius (L.) Link; Euonymus europaeus L.; Ilex aquifolium L.; Ligustrum vulgare L.; Prunus spinosa L.; Salix viminalis L. and Ulex europaeus L.) were investigated in a glasshouse experiment to understand any relation of transpiration induced hydrologic reinforcement with above- and below-ground plant traits (e.g. specific leaf area; root length density). The ten species showed large differences in terms of water uptake, which translated to significant differences in matric suction and soil strength. Species with the largest water uptake increased soil strength more than ten times that in fallow soil. Specific leaf area, root length density and root:shoot ratio were best correlated with the induced hydrologic reinforcement provided by the ten tested species. These results supplied essential species information for designing the subsequent experiments. Based on the previous findings, three representative yet contrasting species (Corylus avellana, Ilex aquifolim and Ulex europaeus) were selected and planted in 1-m soil columns to investigate the effects of season (i.e. summer vs winter), plant functional type (i.e. deciduous vs evergreen) and soil depth on the magnitude and distribution of transpiration-induced matric suction and the associated soil strength gain. Evergreens could slowly induce matric suction and hence potentially stabilise soil during winter. However, there were very large differences between the tested evergreens (I. aquifolium and U. europaeus). Indeed, only U. europaeus provided matric suction and soil strength gain along the entire depth-profile because of its fast growth (above- and below-ground). A full-scale field experiment was also performed to provide ground-truth data on the extent of variation in hydrologic reinforcement among species, hence validating the glasshouse results obtained in the first two studies. The two-year field experiment yielded a similar ranking to the glasshouse experiments in terms of the species ability to rapidly develop matric suction and soil strength. In particular, the evergreen U. europaeus induced large matric suction (e.g. ≥ 70 kPa at 0.5 m depth) even during the early establishment period. Furthermore, this field research highlighted the greater (compared to other tested species) temporal effectiveness of U. europaeus, which was able to provide matric suction on the slope from early spring to late autumn. The greater ability of U. europaeus in inducing and preserving matric suction can be attributed to its large water uptake, which supports its fast growth, as well as to the notable interception loss provided by its canopy. Therefore, U. europaeus can represent a very suitable species for slope stabilisation under the temperate climate context. Root biomechanical properties, including tensile strength and Young's modulus, were investigated in the laboratory for the same ten species. The results highlighted a large variability in the tensile strength-diameter relations during the early stage establishment of plants, especially in thin roots with diameter ranging from 0.4 to 2.0 mm. The root tensile strength-diameter relationships highlighted three different trends. The common negative power relation between root tensile strength and diameter existed only for two out of the ten tested species (i.e. E. europaeus and U. europaeus). B. sempervirens, I. aquifolium and P. spinosa showed a slight increase in tensile strength with increasing root diameter. C. avellana, C. monogyna and L. vulgare consistently showed an initial increase in root tensile strength with increasing root diameter, reaching peak strength between 1.0 and 2.5 mm diameter. Beyond the peak strength, a reduction in strength was observed with increasing root dimeter. These bimodal trends might be partially explained by the differences in the development stage of root primary and secondary structures. Root moisture content can be one of the factors inducing the observed large variability in root tensile strength. Therefore, the last part of this thesis assessed the effects of root drying on the root biomechanical properties of U. europaeus. Root strength and stiffness showed an abrupt increase when root water content dropped below 0.5 g g-1. The strength increase can be explained by the reduction in root diameter and by changes in root properties induced by the root water potential drop. Moreover, root water loss and root strength gain were diameter-dependent because of the relatively larger evaporative surface per volume of thin roots.

The main goal of this research is to evaluate the behavior of earth pressure profiles in unsaturated soils under transient flow. In the first part, an empirical correlation is proposed to obtain the fitting parameters of Brooks and Corey’s soil-water retention model from Fredlund and Xing’s model. The retention models and the proposed equivalency between the models were assessed for 601 soil samples from the unsaturated soils hydraulic database (UNSODA). In the second part, a coupled one-dimensional hydro-mechanical model is introduced and is implemented into Rankine’s earth-pressure model to represent active and passive earth pressure profiles in unsaturated soils under transient flow. A realistic coupling process of infiltration and deformation in the porous medium is established based on the variation in permeability along with deformation in the soil body. The results showed that ignoring the hydro-mechanical coupling effect can lead to underestimation of earth pressure values, especially for fine-grained soils.

The main objective of this research is to present a robust numerical framework based upon Isogeometric analysis (IGA) for simulation of thermo-hydro-mechanical (THM) processes in variably saturated soils. The proposed platform employs the Bézier extraction operator to connect IGA to the conventional finite element analysis (FEA), allowing to take advantage of features offered by the two methods. In the first part, the formulation and numerical implementation for fully coupled numerical simulation of THM problems in saturated porous media are presented. The results are compared against analytical solutions and experimental tests available in the literature. In the second part, the proposed method is used to study the temperature effect on the hydro-mechanical response of sd supporting hydrocarbon pipelines, an aspect that has been overlooked in the majority of previous studies. The results highlight the need for considering nonisothermal behavior in different analysis and design stages of sd-buried pipelines. In the third part, the proposed IGA-FEA framework is extended to evaluate the nonisothermal elasto-plastic behavior of unsaturated soils. Drucker-Prager yield surface is used as criterion to limit the modified effective stress where the model follows small strain, quasi-static loading conditions. The framework is used to simulate strain localization of unsaturated dense sand subjected to undrained compression loading. In comparison with FEA, the present method smoothly distributes plastic strain over the adjacent elements. The parametric study highlights the importance of considering temperature effects in elasto-plastic analysis of unsaturated soils.

Esta Tesis está dirigida al análisis teórico y experimental de problemas acoplados Termo-Hidro Mecánico (THM) que se desarrollan en formaciones geológicas profundas destinadas al almacenamiento de residuos radiactivos de alta actividad. En las últimas décadas, han sido estudiadas las formaciones arcillosas para ser utilizadas como barreras geológicas debido a su reducida conductividad hidráulica. La degradación de las rocas arcillosas producida por efectos de temperatura y por efectos de variación en el grado de saturación, es un factor de fundamental importancia, que es actualmente investigado en ensayos in situ a gran escala, como así también en ensayos de laboratorio. En ésta tesis, la roca Opalinus Clay ha sido ampliamente caracterizada mediante ensayos de laboratorios. Desde un punto de vista macro-estructural se ha obtenido la curva de retención de agua, conductividad hidráulica, resistencia y deformación. El análisis micro-estructural está enfocado a la caracterización mineralógica obtenida por difracción de rayos X, la distribución del tamaño de los poros determinada por porosimetría de mercurio (MIP) y microscopía electrónica (SEM). La tesis describe también un ensayo in situ de calentamiento diseñado para analizar la interacción entre la barrera de ingeniería (bloques de bentonita compactada) y la barrera geológica (Opalinus clay). Esta interacción ha sido analizada a través de simulaciones numéricas realizadas con el código de elementos finitos CODE_BRIGHT. Una célula termo-hidráulica fue especialmente diseñada para observar el comportamiento THM de la roca en condición drenada y no drenada, a través de pulsos de calor. Parámetros térmicos e hidráulicos de la roca fueron determinados por retro análisis a través de simulaciones numéricas realizadas con CODE_BRIGHT. Desde el punto de vista mecánico, un modelo constitutivo ha sido formulado en 3D e implementado en CODE_BRIGHT con el objetivo de reproducir el comportamiento mecánico anisótropo y rotura frágil de las rocas arcillosas. El modelo es formulado en un marco viscoplástico y considera la resistencia y deformabilidad de la matriz y de las juntas. El criterio de falla de la matriz y de las juntas es definido por superficies de fluencias hiperbólicas en el espacio de tensiones p-J y τ−σ, respectivamente. El comportamiento frágil de las rocas arcillosas es simulado por un reblandecimiento isótropo y cinemático definido en términos de trabajo de deformación plástico. El modelo constitutivo ha sido calibrado mediante ensayos triaxiales de laboratorio realizados en especimenes con diferentes ángulos de buzamiento. El modeloconstitutivo anisótropo ha sido aplicado a la simulación numérica en 3D de un ensayo de calentamiento in-situ. Una simulación numérica en 3D de un ensayo de ventilación in-situ realizado en un micro-túnel sin recubrimiento ha sido realizada para reproducir el brusco cambio de permeabilidad por efectos de secado de la roca. En este caso, un modelo hidráulico que considera la apertura de las juntas por efectos de secado ha sido implementado para reproducir los cambios de permeabilidad en excavaciones subterráneas. / This thesis deals with the theoretical and experimental analysis of the coupled Thermo- Hydro-Mechanical (THM) processes developed in geological formations suitable for the repository of radioactive waste of high activity. In the last decades, the argillaceous formations have been studied to be used as geological barriers, due to its reduced hydraulic conductivity. The degradation of clay shales induced by temperature and saturation effects is an important factor which is currently being investigated in large scale in situ tests as well as in laboratory studies. In this thesis, the Opalinus clay rock has been widely characterized by means of laboratory tests. From a macro-structural point of view, the water retention curve, hydraulic conductivity, strength and deformability parameters have been determined. The micro-structural analysis is focused to the mineralogical characterization obtained by means of X ray diffraction, pore size distribution (PSD) determined by means of mercury intrusion porosimetry (MIP) and scanning electronic microscopy (SEM). The thesis describes also a large scale heating in situ test designed to analyze the interaction between the engineer barrier (compacted bentonite blocks) and by the geological barrier, (Opalinus clay). This interaction has been analyzed by means of numerical simulations performed with the finite element code CODE_BRIGHT. A thermo hydraulic cell was specially designed to observe the coupled THM behaviour of the clay shale rock under drained and undrained conditions by means of heat pulses. Thermal and hydraulic parameters of rock were determined by means of back-analysis performed with the help of CODE_BRIGHT. In order to reproduce the anisotropic and brittle behaviour of the clay shale, a 3D mechanical constitutive model has been formulated and implemented in CODE_BRIGHT. The constitutive model is formulated in a viscoplastic framework and it considers the strength and deformability of both matrix and discontinuities (joints). The failure criterion of the matrix and the joints is defined by means of hyperbolic yield surfaces in the p-J and τ-σ stress space, respectively. The brittle behaviour of clay shale is simulated by means of isotropic and kinematic softening defined in terms of a workhardening criterion. The anisotropic constitutive model has been calibrated against triaxial laboratory tests performed on specimens with a main family of discontinuities having different dip angles. The constitutive model has been applied to a 3D numerical simulation of an "in-situ" heating test. A 3D numerical simulation of a ventilation test performed in an unlined micro tunnel was also performed in order to reproduce the changes of the rock permeability by drying effects. In this case, a hydraulic model able to consider the changes in joint thickness by drying effects has been developed to reproduce the changes of permeability in underground excavations.

Glaciation is considered one of the main natural processes that can have a significant impact on the long term performance of DGRs. The northern part of the American continent has been subjected to a series of strong glaciation and deglaciation events over the past million years. Glacial cycles cause loading and unloading, temperature changes and hydraulic head changes at the ground surface. These changes can be classified as transient boundary conditions. It is widely accepted that the periodic pattern of past glacial cycles during the Late Quaternary period are resultant of the Earth’s orbital geometry changes that is expected to continue in the future. Therefore, from the safety perspective of DGRs, such probable events need to be taken into account. The objective of this thesis is to develop a numerical model to investigate the thermo-hydro-mechanical-chemical (THMC) coupled processes that have resulted from long term past and future climate changes and glaciation cycles on a proposed DGR in sedimentary rocks in southern Ontario. The first application is done on a large geological cross section that includes the entire Michigan basin by using a hydro-mechanical (HM) coupled process. The results are compared with field data of anomalous pore water pressures from deep boreholes in sedimentary rocks of southern Ontario. In this work. The modeling results seem to support the hypothesis that at least the underpressures in the Ordovician formation could be partially attributed to past glaciation. The second application is made on site conditions by using the THMC model. The results for the pore water pressure, tracer profiles, permafrost depth and effective stress profile are compared with the available field data, the results show that the solute transport in the natural limestone and shale barrier formations is controlled by diffusion, which provide evidence that the main mechanism of transport at depth is diffusion-dominant. The third application is made on site conditions to determine the effect of underground changes in DGRs due to DGR construction. The results show that future glaciation loads will induce larger increases in effective stresses on the shaft. Furthermore, it is found that hypothetical nuclide transport in a failed shaft can be controlled by diffusion and advection. The simulation results show that the solute transported in a failed shaft can reach the shallow bedrock groundwater zone. These results might imply that a failed shaft will substantially lose its effectiveness as a barrier. The fourth application is proposed to investigate the geochemical evolution of sedimentary host rock in a near field scale. In this part, a new thermo-hydro-mechanical-geochemical simulator (COMSOL-PHREEQC) is developed. It is anticipated that there will be a geochemical reaction within the host rock that results from interaction with the water enriched with the CO2 generated by nuclear waste.

The management of radioactive wastes is a significant environmental issue facing the international nuclear community today. The current international consensus is for disposal of higher activity waste from a variety of sources in deep geological disposal facilities (GDFs). Hydraulic seals, often planned to consist of compacted bentonite-sand blocks, are an important part of the closure phase of a GDF. As such, an understanding of the hydro-mechanical (HM) behaviour of these seals, and the ability to model and predict their behaviour is fundamental to support many planned safety cases and licence applications. Bentonite is well suited for use as a hydraulic seal due to its high swelling capacity that enables it to swell into voids while maintaining a low permeability sealed barrier to advective flow, and to provide structural support by generating a swelling pressure on the excavation walls. The hydro-mechanical process of bentonite hydration is a highly non-linear problem. As such, coupled process models that are able to account for the strong inter-dependence of the hydraulic and mechanical processes are employed to simulate the behaviour of bentonite under repository conditions. This thesis reports the development of an HM coupled model in the open source finite element code OpenGeoSys (OGS), and its application to the simulation of a range of hydraulic seal test conditions. The developed model couples Richards’ equation for unsaturated flow to a new strain dependent non-linear elastic mechanical model that incorporates a Lagrangian moving finite element mesh to inform the material non-linearity. Stress and volumetric dependent water retention behaviour are incorporated through the implementation of the Dueck suction concept extended to take into account non-recoverable strains during consolidation. A number of permeability functions are implemented and tested against experimental data. The mechanical model is extended to account for wetting-induced collapse behaviour by the definition of a failure curve derived from experimental results. Similar in definition to the Loading-Collapse curve in elasto-plastic models, this failure curve triggers the application of a source term to account for wetting-induced collapse. Coupling between the hydraulic and mechanical processes is achieved through the stress dependency of the water retention behaviour, the inclusion of a new coupling factor for the hydraulic contribution to the mechanical process, and the dependency of numerical convergence criteria on net mean stress. An explicit iterative calculation approach is employed. As a result, the hydraulic and mechanical moving meshes are decoupled to allow volumetric dependent parameters to be updated within process iterations. The model is calibrated and compared to experimental data from the SEALEX experiments conducted by the Institut de Radioprotection et de S ˆ uret´e Nucl´eaire (IRSN) at the Tournemire URL, France. The experimental programme comprises standardised laboratory tests, a 1/10th scale mock-up of a hydraulic seal with a uniform technological void, and a full scale in situ performance test with a non-uniform technological void due to its horizontal geometry. Using a model with 5 hydraulic parameters, 8 mechanical parameters with an experimentally defined failure curve, and one coupling parameter, the major trends of behaviour in all the SEALEX experiments can be recreated, including axial stress build up, water uptake, and final deformation. However, the elastic method employed leads to an over prediction of the rebound on loss of axial confinement in the 1/10th scale mock-up test. Simulations suggest that the non-symmetric technological void in the full scale performance test could have lasting effects on the development of heterogeneity in the hydraulic seal. The development of heterogeneity does not adversely affect the permeability with respect to the design criteria, but may have significant consequences for the development of a heterogeneous swelling pressure.

Le traitement à la chaux est une technique qui améliore considérablement la maniabilité et le comportement mécanique des sols à problèmes. Cependant, la durabilité de ce traitement dans les ouvrages en terre sur le long terme représente un enjeu important pour leur stabilité. En outre, la procédure de mise en place, et par conséquent, la taille des agrégats qui en résulte, est un paramètre essentiel qui peut influencer le comportement des sols traités à la chaux utilisés dans le domaine de la construction d’ouvrages. Ce travail de thèse vise à étudier le comportement thermo-hydro-mécanique des sols traités à la chaux, et plus particulièrement les effets du temps de cure et de la taille des agrégats. Des échantillons de sols limoneux et argileux traités à la chaux ont été préparés avec des agrégats de différentes tailles puis soumis à des temps de cures plus ou moins longs. Ces matériaux ont ensuite été étudiés à travers des observations de la microstructure, des analyses minéralogiques, des mesures de la conductivité thermique, de la perméabilité à l’air et de la capacité de rétention d'eau, complétées par de la détermination de la compressibilité et des mesures des modules de cisaillement en petites déformations. Les résultats montrent que le traitement à la chaux modifie de manière significative le comportement thermo-hydro-mécanique des sols. De plus, le comportement des sols traités est fortement influencé par la taille des agrégats. Plus celle-ci est grande, plus la conductivité thermique et la perméabilité à l'air est importante. En revanche, la capacité de rétention en eau est diminuée de même que la compressibilité et la rigidité du sol / Lime treatment is a technique which greatly improves the workability and the mechanical behaviour of problematic soils. However, the sustainability of this treatment in the earthworks for the long term is an important issue for their stability. Besides, the aggregate size resulting from the construction procedure is an essential parameter that may influence the behaviour of treated soils in field construction. The present work deals with the thermo-hydro-mechanical properties of lime-treated soils, with an emphasis put on the curing time and the aggregate size effects. Lime-treated soil samples (both silt and clay) were prepared with different sizes of aggregates and cured during different periods. Afterwards, these soils were studied through microstructural observations, mineralogical analyses, thermal conductivity, air permeability and water retention capacity measurements, as well as the determinations of compressibility and small strain shear modulus. The results show that significant changes of thermo-hydro-mechanical behaviour of soils are induced by lime treatment after curing. Moreover, the aggregate size also plays an essential role in the behaviour of treated soils. Samples prepared with the large aggregates present higher thermal conductivity and air permeability, but with lower water retention capacity, poorer compression behaviour and smaller stiffness

The shear strength of soil-structure interfaces is relevant to the stability of energy piles. The thermo-hydro-mechanical processes can have a strong effect on the behaviour of interfaces between unsaturated soils and piles. Temperature changes lead to water movement in the soil. The moisture loss or gain in the soil causes drying or wetting. In addition, water movement influences the heat transfer properties of the soil. Temperature and moisture content changes affect the magnitude of soil suction in unsaturated soils. Changes in soil suction alter the strength and deformation characteristics of the soil mass and soil-structure interfaces. Similar to the effects of temperature changes, the mechanical loading and the changes in hydraulic conditions in the ground would cause changes in the void ratio, degree of saturation, suction, strength and deformation characteristics of soil. The interface behaviour under varying thermo-hydro-mechanical (THM) conditions is classified as a coupled problem and this is the subject of the present research. In the present investigation, laboratory studies and numerical analyses are carried out to evaluate the THM effect on the behaviour of interfaces between an energy pile material and an unsaturated soil. A 3D interface apparatus (Fakharian and Evgin 1996) has been modified (Fu et al. 2013) to allow the behaviour of an interface to be studied under thermo-mechanical loading conditions. In the present study, the experiments are conducted on soil samples with low degree of saturation and high degree of saturation. It is found that in interface tests using soil samples with low degree of saturation, the adhesion increased due to a positive effect of suction on strength than the negative effect of increasing temperatures. However, in interface tests on soil samples with high degree of saturation, the adhesion decreased with increasing temperatures while the positive effect of suction was not large enough to overcome the negative effect of increasing temperatures. This is a new finding that has not been reported anywhere in the literature. The friction angle for both soil samples (with different degrees of saturation) changed slightly with temperature change. Coupled finite element analyses conducted in the present study provide the following geotechnical information that would be useful for the design of energy piles: (a) Bearing capacity of the pile with and without the effect of temperature, (b) The effect of degree of saturation (or suction) on the strength and deformation characteristics of both the soil and the soil-structure interface, (c) Temperature effects on the amount of pile head movements (up or down), (d) Temperature induced stresses in the pile, (f) Amount of heat that can be stored or extracted from the ground as a function of time. At the initial stages of this study, THM effects on the behaviour of energy piles under saturated and unsaturated conditions are analyzed by using SIGMA/W and VADOSE/W finite element codes of GeoStudio 2012. Although these codes are not multi-physics FE codes, it is possible to use them sequentially to obtain results that will show the trends in pile behaviour. This numerical approach is used first to analyze the behaviour of an energy pile installed partially in unsaturated soil. The moisture content and temperature distributions around a 10 m long, bored pile are calculated using transient analyses. Changes taking place in the stress state along the pile shaft and the bearing capacity of the pile at different temperatures are calculated. In the second part of the numerical analysis of the present study, THM effects on the behaviour of energy piles under saturated and unsaturated conditions are analyzed by using PLAXIS 2D finite element code. PLAXIS is a fully couples finite element code. In order to enhance present understanding of the behaviour of energy piles and do the analysis correctly, a fully coupled analysis involving thermo-hydro-mechanical processes was carried out. Three simulations (mechanical loading only, thermo-mechanical coupling and thermo-hydro-mechanical coupling) are conducted using case studies that are available in the literature. In addition, the behaviour of a generic energy pile, which is installed in a kaolin-sand mixture, is studied by taking into consideration of thermo–hydro-mechanical processes. The coupled analysis provided the distributions of temperature, degree of saturation, suction and heat flux in the analysis domain. Numerical results of the fully-coupled method are compared with the results of sequential method of analysis.

Glaciation is considered one of the main natural processes that can have a significant impact on the long term performance of DGRs. The northern part of the American continent has been subjected to a series of strong glaciation and deglaciation events over the past million years. Glacial cycles cause loading and unloading, temperature changes and hydraulic head changes at the ground surface. These changes can be classified as transient boundary conditions. It is widely accepted that the periodic pattern of past glacial cycles during the Late Quaternary period are resultant of the Earth’s orbital geometry changes that is expected to continue in the future. Therefore, from the safety perspective of DGRs, such probable events need to be taken into account. The objective of this thesis is to develop a numerical model to investigate the thermo-hydro-mechanical-chemical (THMC) coupled processes that have resulted from long term past and future climate changes and glaciation cycles on a proposed DGR in sedimentary rocks in southern Ontario. The first application is done on a large geological cross section that includes the entire Michigan basin by using a hydro-mechanical (HM) coupled process. The results are compared with field data of anomalous pore water pressures from deep boreholes in sedimentary rocks of southern Ontario. In this work. The modeling results seem to support the hypothesis that at least the underpressures in the Ordovician formation could be partially attributed to past glaciation. The second application is made on site conditions by using the THMC model. The results for the pore water pressure, tracer profiles, permafrost depth and effective stress profile are compared with the available field data, the results show that the solute transport in the natural limestone and shale barrier formations is controlled by diffusion, which provide evidence that the main mechanism of transport at depth is diffusion-dominant. The third application is made on site conditions to determine the effect of underground changes in DGRs due to DGR construction. The results show that future glaciation loads will induce larger increases in effective stresses on the shaft. Furthermore, it is found that hypothetical nuclide transport in a failed shaft can be controlled by diffusion and advection. The simulation results show that the solute transported in a failed shaft can reach the shallow bedrock groundwater zone. These results might imply that a failed shaft will substantially lose its effectiveness as a barrier. The fourth application is proposed to investigate the geochemical evolution of sedimentary host rock in a near field scale. In this part, a new thermo-hydro-mechanical-geochemical simulator (COMSOL-PHREEQC) is developed. It is anticipated that there will be a geochemical reaction within the host rock that results from interaction with the water enriched with the CO2 generated by nuclear waste.