Search

International audience; The Callovo-Oxfordian (COx) claystone is considered as a potential host rock in the French concept of high level radioactive waste disposal at great depth. To better understand and to complement existing published data on the thermo-hydro-mechanical behaviour of the COx claystone, an experimental program was carried out by using a hollow cylinder triaxial device specially developed for low permeability materials. Special care was devoted to the saturation of the specimens that was made under stress conditions close to in-situ, and to conditions ensuring full drainage thanks to a reduced drainage length and low shear rate. Tests were carried out under in-situ, half to in-situ and twice the Terzaghi mean effective in-situ stress at 25°C and 80°C to investigate the effects in the close field of the temperature elevation due to the exothermic nature of the waste. Some radial permeability tests were conducted at various temperatures. The data obtained showed that there is little effect of temperature on the elastic parameters determined, whereas a tendency to a decrease in shear strength was noted, compatible with the few published data. Temperature also appeared to have little effect on the intrinsic permeability, with higher flows mainly due to the decrease in water viscosity.

International audience; This study aims at investigating the lime treatment effect on the changes in microstructure and water retention property of compacted saline soil, with consideration of the aggregate size effect. Two soil powders with different maximum aggregate sizes (Dmax = 0.4 and 5 mm) were prepared and stabilized by 2% lime. The microstructure, total suction and matric suction were determined at various curing times. Results showed that the lime treatment caused a rapid decrease in micro-pores and an increase in macro-pores due to the flocculation of soil particles. During curing, the percentage of micro-pores decreased and that of nano-pores increased slightly. Due to the modification of microstructure, the matric suction increased significantly at 90-day curing. However, the curing time effect on the total suction was insignificant. This was due to the fact that the Ca2+ and Mg2+ in soil pore water and the Ca2+ from hydrated lime were consumed in the precipitations of CaCO3 and Mg(OH)2, cation exchanges and pozzolanic reaction, resulting in a reduction in osmotic suction. Therefore, the increase in total suction was slight, as the increase in matric suction was balanced by the decrease in osmotic suction. The treated specimens with larger aggregates exhibited a larger modal size and thus had a smaller air entry value. The aggregate size effect on the water retention property of total suction and matric suction was found to be insignificant, which could be explained by the similar pore size distribution at micro-pore range and the same soil mineralogy for specimens with different aggregates.

International audience; In thermal-related engineering such as thermal energy structures and nuclear waste disposal, it is essential to well understand volume change and excess pore water pressure buildup of soils under thermal cycles. However, most existing thermo-mechanical models can merely simulate one heating–cooling cycle and fail in capturing accumulation phenomenon due to multiple thermal cycles. In this study, a two-surface elasto-plastic model considering thermal cyclic behavior is proposed. This model is based on the bounding surface plasticity and progressive plasticity by introducing two yield surfaces and two loading yield limits. A dependency law is proposed by linking two loading yield limits with a thermal accumulation parameter nc, allowing the thermal cyclic behavior to be taken into account. Parameter nc controls the evolution rate of the inner loading yield limit approaching the loading yield limit following a thermal loading path. By extending the thermo-hydro-mechanical equations into the elastic–plastic state, the excess pore water pressure buildup of soil due to thermal cycles is also accounted. Then, thermal cycle tests on four fine-grained soils (natural Boom clay, Geneva clay, Bonny silt, and reconstituted Pontida clay) under different OCRs and stresses are simulated and compared. The results show that the proposed model can well describe both strain accumulation phenomenon and excess pore water pressure buildup of fine-grained soils under the effect of thermal cycles.

International audience; An accurate monitoring of axial and radial thermal strains of specimens of the Callovo–Oxfordian claystone, heated under constant confining stress conditions close to that prevailing in the Bure Underground Research Laboratory at 490 m depth, evidenced a particular behavioural feature. The effect of the transverse isotropy of the claystone on thermal strains was not only confirmed, but it was also shown that the thermo-elasto-plastic overall volumetric response was mainly due to the axial response, in which some influence of the adsorbed water is suspected. Conversely, the reversible radial response observed along a temperature cycle could be modelled through a simple homogenisation method that confirmed that it was governed by the thermo-elastic expansion/contraction response of the constitutive minerals. Hence, the simultaneous occurrence of elastic thermal radial strains and elasto-plastic thermal axial strains was evidenced.

International audience; To better understand the salinity effect on the compaction behaviour of soil, standard Proctor compaction test was conducted on soil samples with different salinities. Matric suction and small strain shear modulus, Gmax, were determined and pore size distribution was also investigated on samples statically compacted at different water contents. Results showed that with the decrease of soil salinity from initial value of 2.10‰ (g of salt/ kg of dry soil) to zero, the maximum dry density increased and the optimum water content decreased, whereas there was no significant change with the increase of soil salinity from 2.10‰ to 6.76‰. Interestingly, it was observed that, Gmax also decreased when the soil salinity decreased from initial value of 2.10‰ to zero and kept almost constant when the soil salinity increased from 2.10‰ to 6.76‰, for dry samples with similar matric suction and also for samples compacted at optimum and on wet side whose matric suctions were slightly different due to the difference in remolded water content. Furthermore, the effect of salinity on compaction behaviour and Gmax decreased for samples compacted from dry side to wet side. The pore size distribution exhibited bi-modal characteristics with two populations of micro-pores and macro-pores not only for samples compacted on dry side and at optimum state, but also for those compacted on wet side. Further examination showed that the modal size of micro-pores shifted to lower values and that of macro-pores shifted to higher values for saline soil compared to the soil without salt.

International audience; Based on long term investigations of the microstructure of various geomaterials as 14 different as sensitive low plastic clays from Eastern Canada, unsaturated compacted silt from 15 the Paris area, highly plastic compressible deep marine clay from the Gulf of Guinea, 16 compacted MX80 bentonite and the Callovo-Oxfordian claystone, considered as possible 17 barriers in deep geological radioactive waste disposal, two fundamentals and distinct nano 18 and micro mechanisms governing their macroscopic volume changes have been identified. In 19 low plastic structured clays and dry compacted soils, in which an aggregate microstructure has 20 been evidenced, the decrease in volume under mechanical compression result from the 21 collapse of inter-aggregates pores in an ordered manner, from the larger to the smaller, with 22 no effect on the intra-aggregate porosity. The soil skeleton can hence be modelled as an 23 elastic fragile porous matrix, affected by the ordered collapse of its pores. Things are different 24 in plastic soils, due to the significant reactivity of the montmorillonite minerals to changes in 25 water content that results in significant changes of the initial porous matrix. The ordered 26 adsorption of layers of water molecules in clay platelets with respect to the suction or stress 27 applied, evidenced long time ago in Soil science through X-ray diffraction techniques, appear 28 to be able to help better understanding various phenomena like the compression of plastic 29 compressible soils and the hydration of compacted bentonites. Interestingly, it also applies to 30 understand the effects of smectite minerals in the volume changes behaviour of the Callovo-31 Oxfordian claystone. These two mechanisms at nano and microscopic scales hence provide a 32 better understanding of the macroscopic volume changes of a large variety of natural and 33 compacted clayey soils and rocks. 34 Keywords: clayey soils and rocks; microstructure; montmorillonite; pore size distribution; 35 nano scale; water adsorption. 36 37 2

International audience; Pellet-based expansive clay materials are considered as a sealing material for closing the galleries in radioactive waste disposal concepts. In repository conditions, the granular mixture progressively homogenises upon hydration by the host rock pore water. The present study focuses on the material behaviour before homogenisation. A grain-scale experimental characterisation is first performed in the laboratory. A model describing the hydromechanical behaviour of a pellet is proposed based on the experimental results. Then, suction-controlled swelling pressure tests are performed in the laboratory. Using Discrete Element Method (DEM) and the model proposed for a single pellet, the tests are successfully simulated. It is highlighted that (i) the swelling pressure evolves in two phases in the investigated suction range, controlled by the granular structure of the mixture; (ii) wall effects at the laboratory scale affects the material response; (iii) measurement variability associated to the sensor diameter is non-negligible; (iv) DEM is a valuable tool able to provide insight into the material behaviour.

International audience; In the laboratory, the instantaneous profile method has been routinely applied to determine the hydraulic conductivity of unsaturated compacted clayey soils. But the application of this method is often limited by the large-dimensions of water content probes such as TDR (Time Domaine Reflectometry) probes. Indeed, the existing commercial TDR probes are too large to match the small dimensions of laboratory samples. Furthermore, this method is difficult to be applied to natural stiff clays or other stiff materials (lime/cement treated soils for instance) owing to the surface irregularity created during the sample preparation. The voids between soil surface and testing cell would give rise to side wall leakage during water infiltration under constant-volume condition. This paper attempts to solve these problems by using resistant cohesive filament tape to wrap the soil sample for sidewall leakage prevention and keep the specimen in constant-volume condition. A set of home-made miniature TDR probes were developed for volumetric water content monitoring, together with a set of relative humidity sensors for suction monitoring. As expected, the hydraulic conductivity of stiff Teguline clay which was taken from the area of Albian Paris Basin was found decreasing with the increase of suction. Moreover, the value of hydraulic conductivity at zero suction determined by extrapolation is very close to that determined directly by constant head method. This confirms the promising use of miniature TDR probes in water content monitoring, as well as the effectiveness of resistant filament tape in sidewall leakage prevention under constant-volume condition. The successful incorporation of miniature TDR probes and resistant filament tape extends the common instantaneous profile method to small laboratory samples and stiff materials.

International audience; Drained triaxial testing is challenging in low-permeability claystones (10−20 m2). This paper presents a method of testing low-permeability clay rocks in a standard triaxial cell. In this system, the resaturation of the specimen and the drainage conditions were enhanced by reducing the drainage length to 19 mm, the specimen radius. To do so, two geotextiles were placed around the top and bottom ends of the specimen, with no connection between them. Resaturation was hence performed by forcing water infiltration into the specimen from the upper and lower geotextiles, with a maximum infiltration length of around 19 mm, resulting in reasonable saturation durations. High-precision local measurements of radial strains were also achieved by ensuring direct contact between the LVDT rod and the specimen through the membrane. A poroelastic numerical calculation was carried out, and it was shown that, with these drainage conditions, a strain rate of 6.6 × 10−8 s−1 was satisfactory to ensure good drainage when shearing claystone specimens. After a check test made on a low-permeability sandstone with well-known mechanical characteristics, two tests were carried out to investigate specimens of the Callovo-Oxfordian claystone, a possible host rock for deep geological disposal in France. The results compare well with other published data from drained triaxial tests.

In the conventional French railway substructures, a layer namely interlayer was created naturally by the interpenetration of ballast and subgrade. The lower part of this interlayer is characterized by a matrix of fines with inclusion of coarse grains in it. Moreover, the coarse-grain content is decreasing over depth. In this study, the effect of volumetric content of coarse grains f v (volumetric ratio of coarse grains to the whole sample; grain size > 2 mm) on the mechanical behavior of the lower part interlayer soil was investigated by carrying out monotonic triaxial tests. The results showed that increasing the volumetric content of coarse grains f v led to more significant dilatancy. The shear strength also increased with the increase of f v and the increasing trend appeared to be much more significant when f v >20%. Examination of the variations of peak deviator stress with f v revealed the existence of a characteristic value of fv-cha ≈ 27% that separates two zones with different coarse-grain effects: a fine-fine contact dominating zone when fv ≤ 27% and a grain-grain contact dominating zone when fv > 27%. To clarify the observed phenomena, X-ray microcomputed tomography (μCT) scans were performed on the as-compacted samples, allowing the coarse-grain distribution inside the as-compacted sample to be visualized. It was found that when f v ranged from 0% to 10%, the skeleton of the sample was mainly constituted by fines with the coarse grains floating in the fines matrix. By contrast, when f v reached 20%, the coarse grains formed some aggregates but the fine-fine contacts were still dominating. When f v increased up to 35%–45%, the skeleton of the sample turned to be dominated by the coarse grains. This suggests that the characteristic volumetric content of coarse grains identified through monotonic triaxial test results corresponds to the transition of soil fabric from fine-fine contacts to grain-grain contacts.

International audience; Lime treatment can enhance the workability and hydro-mechanical properties of soil through different physical-chemical reactions. Nevertheless, the beneficiary effect of lime treatment can be altered when the soil was exposed to wetting-drying cycles, depending on the wetting fluid and soil state. In the present study, the changes in small strain shear modulus (Gmax) and microstructure of a compacted lime-treated silt under wetting-drying cycles were studied. The untreated state of soil was also considered for comparison. Meanwhile, the effects of wetting fluid (deionized water and synthetic seawater) and maximum soil aggregate size (Dmax = 0.4 mm for S0.4 and 5 mm for S5) were investigated. Results showed that Gmax increased significantly for the lime-treated soil over curing, and increased slightly for the untreated soil. The untreated specimens were softened and damaged by wetting-drying cycles, while the lime-treated specimens exhibited good resistance with the pore size distributions almost kept reversible along the wetting-drying paths. The subsequent more intensive drying resulted in a significant fabric alteration with occurrence of shrinkage-related fissures of the clay part. However, these fissures were almost healed with rewetting. Thereby, the Gmax of lime-treated soil showed a constant decreasing trend with wetting and an increasing trend with drying. Moreover, Gmax decreased slightly with wetting-drying cycles for the lime-treated specimens wetted by deionized water, suggesting that the wetting-drying indeed softened the soil. However, Gmax increased for the lime-treated specimens wetted by synthetic seawater, due to the more production of cementitious compounds promoted by salts. The lime-treated specimens S0.4 wetted by synthetic seawater had higher Gmax than those wetted by deionized water, while the wetting fluid had insignificant effect on the Gmax of specimens S5 due to the limited promotion of pozzolanic reaction and negligible soil aggregation induced by salts.

For the French conventional railway lines, a layer, namely interlayer, was created in the substructure mainly by the interpenetration of ballast grains and subgrade soils. The in situ investigation indicated that the content of coarse grains decreases over depth. In this study, the resilient modulus and damping ratio of the unsaturated lower part of the interlayer soil were investigated at six different volumetric inclusion contents fv (volumetric ratio of dry coarse grains to the whole sample) by carrying out cyclic triaxial tests following a multi-step loading procedure. The results show that the two dynamic parameters (resilient modulus and damping ratio) change significantly at the beginning of loading and the variation rate decreases as the number of cycles increases. Besides, a mean characteristic volumetric inclusion content fv–cha ranging from 27.8% to 28.9% was identified, separating two zones with different inclusion effects. To verify this observation, X-ray microcomputed tomography (μCT) scans were conducted on as-compacted samples. The results obtained strongly support the existence of fv–cha: when fv ≤ fv–cha, the matrix of fines constitutes the skeleton of the sample with inclusions floating in it, leading to slight changes of the two dynamic parameters with fv. By contrast, when fv > fv–cha, the inclusions dominate the skeleton of the sample, giving rise to significant changes of the two dynamic parameters with fv.

International audience; 22 23 The ConVergence-ConFinement (CV-CF) method is widely used in conventional tunneling at 24 a preliminary stage of the design. In this method, the rock-support interaction is simplified by 25 means of a two-dimensional plane-strain assumption. However, when the ground exhibits large 26 deformation and/or when the support is very stiff and installed close to the tunnel face, the 27 results obtained with the CV-CF method may significantly differ from those obtained using 3D 28 numerical computations. The strong interaction taking place between the rigid lining and the 29 rock mass is not considered in the most common use of the CV-CF method. Some 30 improvements of the CV-CF method as the so-called implicit methods have been developed in 31 order to better account for this interaction. 32 In this paper, the applicability of the CV-CF methods is discussed for full face excavation 33 tunneling with a stiff support system. An in-depth comparison between plane-strain closed form 34 solutions and numerical results which properly accounts for the 3D effects at the vicinity of the 35 tunnel face is carried out. The range of application of the different approaches of the CV-CF 36 method is discussed. Finally, some simple empirical formula which can be used in preliminary 37 design for a large range of ground conditions are proposed. 38 39

International audience; This study presents a full-scale model investigation on variations of soil stress in a geosynthetic-reinforced pile-supported track bed at various water levels and loading cycles, with four testing procedures: water level rising, cyclic loading at high water level, water level lowering, and cyclic loading at low water level. The soil arching effect was revealed, characterized by higher stress above the pile cap. With the water level rising and loading cycles increasing at high water level, this effect becomes more pronounced, until a peak value of dynamic stress concentration ratio is reached. The stable state of soil arching is obtained earlier near the crown of soil arching, but this arching effect develops more significantly at the foot of soil arching. With the water level lowering and loading at low water level, the soil arching effect remains steady, with slightly changed dynamic stresses in the track bed. The geogrid shows a significant impact on the load transfer mechanism for the quasi-static stress: the quasi-static pile-cap stress presents higher values below the geogrid, whereas the opposite trend is observed for the water-bag (subsoil) area. Nevertheless, this mechanism is not obvious with respect to the dynamic stress, with the values showing no distinct difference above and below the geogrid.; Cette étude présente une étude de modèle grandeur nature sur les variations des contraintes du sol dans des plates-formes sur pieux renforcées par géosynthétique à différents niveaux d’eau et cycles de chargement, avec quatre procédures d’essai : élévation du niveau d’eau, chargement cyclique à niveau d’eau élevé, abaissement du niveau d’eau et chargement cyclique à niveau d’eau bas. L’effet de voûte du sol a été révélé, caractérisé par une contrainte plus élevée au-dessus du chapeau de pieu. Lorsque le niveau d’eau augmente et que les cycles de chargement augmentent à niveau d’eau élevée, cet effet devient plus prononcé, jusqu’à ce qu’une valeur maximale du rapport de concentration des contraintes dynamiques soit atteinte. L’état stable des voûtes du sol est obtenu plus tôt près du sommet de voûte du sol, mais cet effet de voûte se développe de manière plus significative au pied de voûte du sol. Avec l’abaissement et le chargement du niveau d’eau à un niveau d’eau bas, l’effet de voûte du sol reste stable, avec des contraintes dynamiques légèrement modifiées dans la plate-forme de la voie. La géogrille montre un impact significatif sur le mécanisme de transfert de charge pour la contrainte quasi-statique : la contrainte quasi statique de chapeau de pieu présente des valeurs plus élevées sous la géogrille, tandis que la tendance inverse est observée pour la zone du sous-sol. Néanmoins, ce mécanisme n’est pas évident pour la contrainte dynamique, les valeurs ne montrant aucune différence nette au-dessus et en dessous de la géogrille

International audience; An energy approach is proposed as a complement to the stress approach commonly considered for investigating soil desiccation cracking. The elastic strain energies before and after crack initiation are estimated by both numerical and analytical solutions. The energy released by cracking is then compared with the fracture energy to discuss crack initiation conditions. This leads to combined energy and stress conditions for crack initiation following Leguillon's theory. An approximate analytical solution is derived from a variational formulation of the porous elastic body equations. A cohesive zone model and finite element code are used to simulate crack propagation in an unsaturated porous body. This analysis shows that the energy criterion is reached before the stress criterion, and this can explain unstable crack propagation at the beginning. The approximate analytical solution allows predicting correctly the crack depth and opening in its initiation stage.

International audience; The water retention, compressibility and swelling properties of a pellet/powder bentonite mixture were investigated in the laboratory. The water retention capacity was determined under constant-volume condition using a specially designed cell allowing vapor exchange in all directions; suction controlled oedometer tests were carried out for the compressibility investigation; both constant-volume and swell-consolidation methods were applied for the swelling pressure determination. The vapor equilibrium technique was used for suction control. Comparable results were found for the water retention capacity of the pellet/powder mixture determined under constant-volume condition and one single pellet under free swelling condition for suctions higher than 4 MPa, suggesting that the suction was mainly controlled by the micro-pores inside the pellets/powder grains and the swelling of the clay particles was accommodated by the existing macro-pores. On the contrary, at lower suctions, the constant-volume conditions gave rise to a lower water retention capacity for the mixture, indicating the restricted clay particle swelling after the filling-up of the existing macro-pores. Oedometer compression curves revealed a different behavior for low and high suctions: at high suctions, the volume change behavior was governed by the pellets rearrangement combined with possible pellets crushing upon loading. By contrast, at low suctions, the mixture lost its initial granular structure during suction decrease; thus, the volume change behavior became similar to that of compacted bentonite. Compared to compacted bentonite, the pellet/powder mixture showed a lower yield stress. A lower value of swelling pressure was found with the constant-volume method, confirming the limitation of the swell-consolidation method in determining soil swelling pressure.

International audience; In the present work, the shear behaviour of soils and the soil–concrete interface is investigated through direct shear tests at various temperatures. A conventional direct shear apparatus, equipped with a temperature control system, was used to test sand, clay, and the clay–concrete interface at various temperatures (5, 20, and 40 °C). These values correspond to the range of temperatures observed near thermoactive geostructures. Tests were performed at normal stress values ranging from 5 to 80 kPa. Results show that the effect of temperature on the shear strength parameters of soils and the soil–concrete interface is negligible. A softening behaviour was observed during shearing of the clay–concrete interface, which was not the case with clay specimens. The peak strength of the clay–concrete interface is smaller than the ultimate shear strength of clay.

International audience; The pile (and micropile) group effect in sand remains a key issue in civil engineering. This paper describes an experimental study carried out using a calibration chamber and an instrumented model pile installed by jacking. A specific methodology is proposed to study group effect through a generic pile within the group. A pile group can be modeled by a group of five piles, one central pile and four adjacent piles. The central pile represents a generic pile within a group with a large number of piles, and the calibration chamber enables the performance of a parametric study to evaluate the global and local (tip resistance and shaft friction) group effects and quantify them using the efficiency coefficient factors relative to tip resistance and shaft friction. The effect of parameters, such as the pile-to-pile spacing ratio and the installation order on pile group response has been investigated. The instrumented generic pile is designed to study independently tip resistance and shaft friction.The results show that the installation order has a significant influence on the pile group response. Some recommendations from laboratory tests are proposed to optimize pile installation in the case of a group and benefit from group effect.

International audience; This paper aims to model the thermo-mechanical behavior of saturated clays under undrained conditions. Classic thermo-hydro-mechanical formulations obtained using different approaches were compared and discussed, showing their compatibility and differences. A thermo-elasto-plastic model called TEAM, using a two-surface approach, was developed for saturated clays under undrained conditions in the framework of thermo-poro-mechanics. The aim of the model is to predict a smooth transition between the elastic and elastoplastic states. Two additional physical parameters, namely volumetric thermal expansion coefficient and pore water compressibility, were back analyzed from the results of the undrained heating tests. By simulating experiments found in the literature, it was shown that this model is appropriate in capturing the evolution of pore water pressure of saturated clays under non-isothermal undrained conditions.

International audience; Methane hydrate is being considered as a potential future energy source but may at the same time constitute a considerable geo-hazard. In the present study, methane hydrate bearing sand sediment was created by pressurizing methane gas into previously moistened, then chilled, packed sand specimen (excess gas method). The excess gas was then replaced by water at high pressure. Afterward, a heating/cooling cycle was applied under undrained conditions, in order to completely dissociate gas hydrates and then recreate them inside the specimen. Finally, the pore pressure was reduced to the atmospheric pressure to dissociate gas hydrates. The whole process was performed in a magnetic resonance imaging (MRI) system, allowing the determination of water and/or gas and hydrate quantity (and spatial distribution) at various times. The MRI signal was finally analyzed to interpret various processes in sand sediment: initial hydrate formation, heating-induced hydrate dissociation, cooling-induced hydrate re-formation, and depressurizing-induced hydrate dissociation.

International audience; This paper summarizes the findings of various investigations carried out for some time in the research group on unsaturated soils at Ecole des Ponts ParisTech. It focusses in more details on the links that can be made between nano, micro, and meso scale phenomena, and the macroscopic response of various Engineered Barrier Systems made up of bentonite, used in various concepts of radioactive waste disposal at great depth. Meso-scale observations using X-Ray microtomography usefully complete some findings established by using more standard techniques of microstructure investigation, like scanning electron microscopy and mercury intrusion porosimetry. The morphology of sand-bentonite and pellet-bentonite powder mixtures can be better understood, together with their changes during hydration. Also, nano-scale mechanisms that govern the hydration of smectites through the consecutive and ordered placement of layers of water molecules along the faces of the smectite minerals are useful for a better understanding of the macroscopic response of Engineered Barrier Systems submitted to hydration under constrained volume conditions.

International audience; An offshore wind farm will be developed in France at the Fecamp site covering in excess of 67 km². In this location, medium to high density chalk containing flint nodules is found. In this paper, some of the hydro-mechanical properties of this specific marine chalk are presented, aiming to characterize the first meters of the chalk more precisely for the design of gravity base foundations. A series of un-drained static and cyclic triaxial tests carried out on 100 mm and 300 mm diameter specimens of weathered chalk are presented. Specimens have been recovered from 100 mm, 300 and 500 mm diameter vibrocore sections. Results show, upon undrained static tests, that the material presents essentially dilative behaviour and usually generates negative excess pore water pressures during shear. Upon undrained cyclic tests, the material shows a progressive development of fairly significant positive excess pore water pressures and relatively high values of axial strains. Results also indicate that the excess pore water pressure dissipation, after a sequence of cycles, induces a densification of the material which results, upon post-cyclic undrained static shear, in a more dilative response resulting in higher values of undrained shear strength.

International audience; Non-compacted pellet/powder bentonite mixtures are considered as candidate sealing plug materials in geological disposals of radioactive waste. Due to its nature, this mixture is characterized by a heterogeneous porosity network, which is responsible for its complex hydro-mechanical (HM) behaviour. The French Institute of Radioprotection and Nuclear Safety (IRSN) has investigated this mixture within the SEALEX project. Both in situ large-scale and laboratory small-scale experiments were carried out. This paper presents the results of a small-scale mock-up test at 1/10th scale of the in situ experiments, in which the pellet/powder mixture was saturated from both sides (top and bottom of the specimen). Both swelling pressure and relative humidity were monitored at several positions of the specimen. Different responses from the sensors were found, depending on the local porosity as well as the evolution of the hydration front. The HM response of the mixture is strongly conditioned by the initial pellet/powder distribution, which depends on the protocol followed for the specimen preparation. After 800-day hydration, an anisotropy was found between the axial and the radial swelling pressures, due to the presence of larger void at the top of the sample and the friction at the cell wall. The sample was still heterogeneous after 800-day hydration mainly due to the initial heterogeneous porosity distribution, combined with the effect of friction and the non-saturation of the mixture. The evolution of injected water with time revealed that the sample was not full saturated after 800-day hydration.

International audience; In the French conventional railway substructure, the interpenetration of ballast grains and subgrade fine soils that occurred over years of operation has created a new layer, namely, an interlayer. The in situ investigation on this interlayer showed that the content of ballast grains decreases over depth, with the lower part characterized by a matrix of fines with inclusions of coarse grains. In this study, the permanent deformation of a material simulating the lower part of interlayer soil was investigated at six different volumetric inclusion contents fv (volumetric ratio of the inclusion grains to the total sample) by performing cyclic triaxial tests. The results indicate that at a given cycle, the permanent deformation decreases with the increase of fv, and the evolution of permanent deformation is strongly influenced by the loading history. To further investigate the effect of inclusion content, a method that allows eliminating the influence of loading history and estimating the end-stage permanent deformations at different stress levels was applied. Quadratic polynomial and bilinear fitting methods were used to fit the variations of the estimated end-stage permanent deformations with fv, showing a proper similarity between the two methods at high loading amplitudes (higher than 15 kPa). Furthermore, the testing results revealed the existence of a characteristic volumetric inclusion content fv-cha by bilinear fitting method, separating two zones with different inclusion effects. This observation is strongly supported by the X-ray microcomputed tomography (μCT) scans performed on the as-compacted samples. When fv ranges from 0 to 20% (smaller than fv-cha), the fines constitute the skeleton of the sample, and the permanent deformation decreases rapidly with the increase of fv. By contrast, when fv increases up to 35–45% (larger than fv-cha), the inclusions dominate the skeleton of the sample, leading to a slight decrease of permanent deformation with fv.

International audience; Non-homogeneity of the pore pressure field in a specimen is an issue for characterization of the thermo-poromechanical behaviour of low-permeability geomaterials, as in the case of the Callovo-Oxfordian claystone (k < 10−20 m2), a possible host rock for deep radioactive waste disposal in France. In tests with drained boundary conditions, excess pore pressure can result in significant errors in the measurement of material parameters. Analytical solutions are presented for the change in time of the pore pressure field in a specimen submitted to various loading paths and different rates. The pore pressure field in mechanical and thermal undrained tests is simulated with a 1D finite difference model taking into account the dead volume of the drainage system of the triaxial cell connected to the specimen. These solutions provide a simple and efficient tool for the estimation of the conditions that must hold for reliable determination of material parameters and for optimization of various test conditions to minimize the experimental duration, while keeping the measurement errors at an acceptable level.

International audience; This paper deals with the resilient behavior of the interlayer soil which is created mainly by the interpenetration of ballast and subgrade soils. The interlayer soil studied was taken from a site in the southeast of France. Large-scale cyclic triaxial tests were carried out at three water contents (w = 4, 6 and 12 %) and three fines contents corresponding to 5, 10 % subgrade added to the natural interlayer soil and 10 % fine particles (

International audience; Due to its heterogeneous nature and the presence of flint nodules, weathered chalk can be difficult to recover offshore in an intact state. On an offshore wind farm site comprising medium to high-density Chalk with flint, several sampling tools have been deployed including Geobor s rotary coring, push sampling, standard vibrocore of 100mm diameter and large diameter vibrocore of 300mm and 500mm diameter. Results of laboratory tests show the impact of the sampling, the sub-sampling and sample diameter on the behaviour of the tested chalk. If the drilling tends to partially remould the chalk, the vibro coring tends to density the chalk, this effect seems to be less pronounced with the increase of core diameter. The different states of densification are difficult to see on the density measurement but more visible on the dilative behaviour observed during the isotropic consolidated triaxial tests. The variation of permeability and the effect of cycles on the behaviour of the chalk are also discussed in the paper.

International audience; This paper summarises some aspects of the methods used in France for designing pile foundations under axial and transverse loadings. These methods mostly use the results of Ménard pressuremeter (MPM) tests and concern the determination of the bearing capacity, as well as the prediction of axial and transverse displacements. The prediction of the bearing capacity from CPT results is also given. After mentioning the general context of foundation design in France, the details of these methods are described and some of their experimental background is explained. These methods are now included in the French standard for pile design (published by AFNOR, Justification of geotechnical work—National application standards for the implementation of Eurocode 7—Deep foundations, 206, 2012), fully compatible with Eurocode 7 on ‘Geotechnical design’.

International audience; A radial injection experimental setup is presented in this paper, which allows one to study the transport and deposition of suspended particles and permeability impairment in porous media. This setup allows one to simulate the conditions of the injection of produced water in oil reservoirs from an injection well. This is achieved by a radial injection of water containing suspended particles of a few microns in size from a central well including a sand screen, through a confined cylindrical sand pack (diameter 52 cm, height 40 cm). A peripheral drainage system permits the recovery of the fluid at the outlet of the sand pack by a collector equipped with a turbidimeter for measuring the concentration of suspended particles. The injection pressure is measured at the inlet, and six pore pressure probes have been installed at different locations inside the sand pack. First experimental results presented show a significant heterogeneity of deposited particle profiles in both radial and axial directions.

International audience; The aggregate size of soils is an essential parameter in lime treatment: the thermo-hydro-mechanical behaviour of lime-treated soils can be greatly affected by the aggregate size of soils before treatment. In particular, the compression behaviour and the pore-size distributions of treated soils are expected to be different with different aggregate sizes, leading to different compressibility and permeability of soils. This study aims to investigate the aggregate size effects on the compressibility and air permeability of a lime-treated soil by performing air permeability measurements in oedometer compression tests on a silt with two different maximum aggregate sizes (Dmax = 5 and 0.4 mm) and treated with 2% quicklime. The tests were performed on both untreated and treated samples at various curing times (t = 7, 28, 60 and 90 days). Results showed that lime treatment significantly improves the compression behaviour of soil due to both the flocculation process and the pozzolanic reaction. The treated samples prepared with smaller aggregates have higher oedometer modulus, suggesting a better lime distribution and the production of more cementitious compounds. Air permeability of soil is strongly related to the aggregate size: the soil with smaller aggregates can have a value of one order of magnitude lower than that with larger aggregates. Further examination showed that in the case of smaller aggregates, the morphology of macro-pores and the efficiency of air flow are more sensitive to lime treatment.

International audience; The Callovo-Oxfordian (COx) claystone is considered as a potential host rock for high-level radioactive waste disposal at great depth in France. Given the exothermic nature of radioactive wastes, a temperature elevation planned to be smaller than 100°C will affect the host rock around the disposal cells. To gain better understanding of the thermal volumetric response of the COx claystone, a new thermal isotropic compression cell was developed with particular attention devoted to monitoring axial and radial strains. To do so, a high precision LVDTs system ensuring direct contact between the LVDT stem and the claystone sample through the membrane was developed. A short drainage length (10 mm) was also ensured so as to allow full saturation of the sample under stress conditions close to in-situ, and fully drained conditions during compression. High precision strain monitoring allowed to observe a volumetric creep under stress conditions close to in-situ. A drained heating test under constant stress carried out afterwards up to 80°C exhibited a thermo-elastic expansion up to a temperature of 48°C, followed by thermoplastic contraction at higher temperature. Creep volume changes, that appeared to be enhanced by temperature, were modelled by using a simple Kelvin-Voigt model, so as to estimate the instantaneous response of the COx claystone and to determine its thermal expansion coefficient. The temperature at which the transition between thermal expansion and contraction appeared is close to the maximum burial temperature of the Callovo-Oxfordian claystone, estimated at 50°C. This is in agreement with what has been already observed on the Opalinus Clay by Monfared et al. (2013) that was interpreted as a thermal hardening phenomenon, showing that the material kept the memory of the highest temperature supported during its geological history.

International audience; This work is devoted to an experimental investigation of the poroelastic behavior of the Callovo–Oxfordian claystone, a potential host rock for the deep underground repository of high-level radioactive waste in France. Drained, undrained, pore pressure loading and unjacketed tests were carried out in a specially designed isotropic compression cell to determine the poroelastic parameters of fully saturated specimens. Great care was devoted to the saturation procedure, and small loading rates were used to ensure full drainage conditions in drained and pore pressure tests (0.5 kPa/min) and in the unjacketed test (2 kPa/min). High-precision strain measurements were performed by ensuring direct contact between the LVDT stems and the specimen. An analysis in the framework of transverse isotropic poroelasticity provided the Biot effective stress coefficients b1 (perpendicular to bedding) between 0.85 and 0.87 and b2 (parallel to bedding) between 0.90 and 0.98 under different stress conditions (pore pressure 4 MPa, total isotropic stresses of 14 and 12 MPa, respectively). A set of equivalent isotropic poroelastic parameters was also determined and a very good compatibility between the results of different tests was found, giving confidence in the parameters determined. The unjacketed test provided a directly reliable measurement of the unjacketed modulus (Ks = 21.7 GPa) that was afterward confirmed by an indirect evaluation that showed the non-dependency of Ks with respect to the stress level. These parameters were obtained for specimens cored and trimmed in the laboratory. A parametric study was then conducted so as to provide an estimation of the parameters in situ, i.e., not submitted to the damage supported by laboratory specimens. A minimal value b = 0.77 seems to be a reasonable lower bound for the equivalent isotropic Biot parameter.

Compacted bentonite-based materials are often used as buffer materials in radioactive waste disposal. When the compacted bentonite blocks are emplaced, technological voids related to different interfaces involving the buffer material are created, and their hydro-mechanical behaviour is of primary importance for the safety of disposal. In this study, the hydraulic resistance of the interface between compacted MX80 bentonite and Boom Clay is investigated in the laboratory using an injection cell. The results obtained show that when water is injected, the technological gap is quickly reduced due to the bentonite swelling. When water pressure reaches the hydraulic resistance of the interface, hydraulic fracturing takes place with a drastic pressure decrease. After fracturing, water injection continues and bentonite continues to swell. A higher subsequent pressure is needed to produce a new hydraulic fracturing. After a certain time, the hydraulic resistance becomes high enough so that no further fracturing occurs, suggesting that the technological gap is sealed.

An experimental programme was carried out with the aim of investigating suction effects in a specimen of Callovo-Oxfordian claystone extracted at great depth (479 m). A specimen that was saturated in an oedometer with limited swelling exhibited significant swelling and desaturation upon quick unloading at constant water content. The microstructure after unloading was compared with the initial microstructure based on mercury intrusion porosimetry measurements. Since the pore size distribution curves before and after loading appeared to be comparable in the range of pore sizes covered by mercury intrusion (entrance diameter between 363ṡ6 μm and 5ṡ5 nm), it was concluded, based on microstructure considerations, that swelling occurred in pores with a diameter less than 5ṡ5 nm, from water transfer within the clay matrix from inter-platelet to intra-platelet pores. This mechanism might occur when excavating galleries in areas of an excavation damaged zone that support instantaneous unloading sequences, as a first desaturation process prior to subsequent evaporation due to the ventilation of galleries.

International audience; Various mechanisms can affect the permeability of dense unconsolidated sands: Volumetric dilation can lead to permeability increase, whereas strain localization in shear bands may increase or decrease the permeability depending on the state of compaction and on the level of grains breakage inside the band. To investigate these various mechanisms, an experimental study has been performed to explore the effect of different factors such as grain size and grain shape, confining pressure, level of shear, stress path, and formation of one or several shear bands on the permeability of dense sands under triaxial loading. The experimental results show a reduction of permeability during the consolidation phase and during the volumetric contraction phase of shear loading, which can be related to the decrease of porosity. The experimental results also show that, depending on the confining pressure, the permeability remains stable or decreases during the volumetric dilation phase despite the increase of total porosity. This permeability reduction is attributed to the presence of fine particles, which result from grains attrition during pre-localization and grains breakage inside the shear band during the post-localization phase.

International audience; This study aims to provide knowledge on the thermo-mechanical behaviour of heat exchanger piles, through a laboratory scale model. The model pile (20 mm in external diameter) was embedded in dry sand. The behaviour of the axially loaded pile under thermal cycles was investigated. After applying the axial load on the pile head, the pile's temperature was varied between 5 °C and 30 °C. Seven tests, corresponding to various axial loads ranging from 0 to 70 % of the pile estimated bearing capacity, were performed. The results on pile head displacement show that heating under low axial load induced heave and cooling induced settlement; the pile temperature-displacement curve was found to be reversible and compatible with the thermal expansion curve of the pile. However, at higher axial loads, irreversible settlement of the pile head was observed after a few thermal cycles. The axial load profile measured by the strain gauges evidenced that the pile head load was mainly transferred to the pile toe. Nevertheless, thermal cycles modified significantly the mobilised skin friction along the pile. The total pressure measured at various locations in the soil mass was also slightly influenced by the thermal cycles.

The soil-atmosphere interaction was investigated by conducting physical model test in the laboratory and by performing numerical analysis using data from an experimental site. For the physical model test, a large scale environmental chamber was developed. This chamber was instrumented by various sensors allowing the soil suction, volumetric water content, and temperature to be monitored at various depths. In the zone occupied by air, temperature, relative humidity and air rate (wind speed) were monitored. The soil surface temperature was also measured by an infrared thermometer. The soil sample was prepared by compaction and wetted from the soil surface before being dried under controlled conditions of relative humidity, temperature and flow rate of air. A camera fixed above the chamber allowed monitoring the development of cracks. The evaporation rate was calculated based on the temperature and relative humidity data at the inlet and the outlet of the chamber, allowing assessment of the performance of the chamber to simulate the evaporation phenomena. The results show that evaporation is a heat consuming process: in the test condition, both air and soil were cooled by the evaporation process. Cracks developed during soil drying. Analysis of the ‘cracking surface ratio’ and ‘weighted width’ showed that the evolutions of these two parameters are similar: thus, in practice, only one is needed for evaporation analysis. For the numerical analysis, a two-dimensional model of soil-atmosphere interaction was developed and implemented in a fully coupled thermo-hydro-mechanical (THM) code. The soil surface boundary conditions were determined from meteorological data using water balance and energy balance equations. The settlement due to soil-atmosphere interaction in an experimental site was simulated. Comparison between calculation and measurement showed that the THM codes can satisfactorily predict the soil settlement, provided that appropriate evapotranspiration models are implemented.

International audience; Gaomiaozi (GMZ) Bent has been recognized as the potential buffer/backfill material for construction of Chinese deep geological repository for disposal of high-level radioactive waste (HLW). For investigation of pressure and suction effects on the thermal volumetric behavior of the highly compacted GMZ01 Bent, a new suction-temperature controlled oedometer was developed. Several suction and pressure controlled cyclic heating and cooling tests have been performed on highly compacted GMZ01 Bent. Suctions ranging from 4 to 110. MPa, temperatures from 25 to 80. °C and vertical loads from 0.1 to 5. MPa were applied. Results show that heating at constant suction and pressure induces either swelling or contraction. At high pressure and low suction, heating tends to induce contraction, while at low pressure and high suction, heating induces expansion. Thermal volumetric strain of GMZ01 Bent tested strongly depends on the overconsolidation ratio (OCR). Two opposite mechanisms are considered to explain the observed phenomena, that is, the volume increase induced by the thermal expansion of the mineralogical components and the adsorbed water and the double-layer thickness at the microstructure level, as well as the volume reduction caused by the macrostructural rearrangements. © 2013 Elsevier B.V.

International audience; In this paper a viscoplastic constitutive model for unsaturated geomaterials is presented. The constitutive laws for the description of the time-dependent mechanical behaviour of saturated and unsaturated geomaterials generalise the isotach approach proposed by Šuklje [52] to the elastoplastic strain hardening based constitutive laws for unsaturated soils. The formulation encompasses strain rate effects and allows the description of the coupled effect of strain rate and suction on the viscoplastic behaviour of geomaterials. The model has been used to simulate tests involving variable stress and/or strain rate conditions, including creep phases and soaking tests. Numerical results demonstrate its reliability in reproducing the general features of the rate-dependent behaviour together with the dependency upon suction. Further tests are currently under consideration to extend model verification to others saturated and unsaturated geomaterials. © 2013 Elsevier Ltd.

International audience; SEALEX is a research project aiming at identifying the key factors that affect the long-term performance of bentonite-based sealing systems with an initial technological void. In this context, a series of in situ experiments have been performed in field conditions. Meanwhile, a small-scale test (1/10) was carried out in controlled conditions in the laboratory, aiming at providing useful information for analyzing the in situ tests in terms of saturation time and sealing effectiveness. In this paper, the results of the small-scale test are presented along with the results from the first in situ test (PT-N1). It was observed that during the saturation process, the evolution of the injected water volume followed a hyperbolic relationship with time in both the laboratory and field conditions. In the laboratory conditions, a decrease in axial swelling pressure occurred due to filling of the technological void. By contrast, this decrease has not been observed in the field conditions. Comparison of the injected water and the axial swelling pressure between the two different scales enabled the definition of a same time upscaling ratio of 2.5 (in situ experiment/small-scale test). Accordingly, the saturation duration of the in situ experiment was estimated to be equal to two years. For the small-scale test, a swelling strain evolution rate of 0.588 mm/day was identified in the case of infiltration from two sides of the sample. This is useful when predicting the evolution of swelling strain in the case of failure of the sealing plug. After filling of an additional 20% void, a swelling pressure of 0.18 MPa was obtained, indicating the favorable sealing capacity of the material after filling the technological void.

International audience; The failure of geomaterials in localised shear bands is one of the most common features in geomechanics. Early studies have provided the necessary criteria for the conditions of localisation, inclination angle with respect to the loading axes and thickness of the shear bands, when loaded at room temperature. This work extends these criteria for the problem of simple shear of a chemically active granular cohesionless material at higher temperatures, where thermal or chemical pressurisation may set in and influence the response of the material. It is deduced that failure occurs at higher positive values of the hardening modulus as temperature increases, that the shear band thickness also depends on the chemical reaction characteristics and that micro-inertia due to grain translations and rotations introduce the necessary rate dependency to regularise the system.

Ch.6 , 518 p

International audience; The paper describes the behavior of remolded kaolin clay reinforced by stone column as investigated in laboratory. The installation of stone column was simulated by performing lateral expansion at different rates within hollow cylindrical remolded kaolin specimens initially subjected to K0 consolidation path. These specimens were, then, subjected to classical consolidated undrained triaxial tests while recording excess pore pressure values. The objective of the experimental programme was to quantify the effects of consolidation stress and stone column on the undrained Young's modulus and shear strength of kaolin clay. Obtained results showed a significant improvement in Young's modulus when the cavity expansion ratio and the consolidation stress increase. It was also found that the increase in undrained shear strength of improved kaolin clay mainly occurred at lower consolidation stress. Another important finding of this study is that the ratio of undrained Young's modulus to undrained shear stress increases when the consolidation stress decreases. Finally, the paper presents a model developed for the design of stone columns. © 2013 Springer Science+Business Media Dordrecht.

International audience; This paper presents a constitutive model for describing some important features of the behavior of natural stiff clay evidenced experimentally such as the limited elastic zone, the presence of strain hardening and softening, and the smooth transition from elastic behavior to a plastic one. The model, namely ACC-2, is an adapted Modified Cam Clay model with two yield surfaces: similarly to bounding surface plasticity theory, an additional yield surface—namely Inner yield surface—was adopted to account for the plastic behavior inside the conventional yield surface. A progressive plastic hardening mechanism was introduced with a combined volumetric-deviatoric hardening law associated with the Inner yield surface, enabling the plastic modulus to vary smoothly during loading paths. The main feature of the proposed model is that its constitutive equations can be simply formulated based on the consistency condition for the Inner yield surface, so that it can be efficiently implemented in a finite element code using a stress integration scheme similar to that of the Modified Cam Clay model. Furthermore, it is proved to be an appropriate model for natural stiff clay: the simulations of a set of tests along different mechanical loading paths on natural Boom Clay show good agreement with the experimental results.

International audience; To better understand the impact of temperature elevation on the response of the excavation damaged zone around repository cells and galleries for radioactive waste disposal, the combined effects of shear and temperature elevation were investigated in the laboratory on the Cal-lovo-Oxfordian claystone. To do so, a hollow cylinder thermal triaxial cell with short drainage path specifically developed for low permeability rocks was used. Once properly saturated under stress conditions close to in situ, the specimen was sheared along a constant effective mean stress path mimicking the stress path followed during gallery excavation. The shear stress was afterwards released and an undrained heating test was performed on the sheared specimen. It was observed that the temperature increase under undrained conditions led to a thermal increase in pore water pressure resulting in a decrease in mean effective stress that brought back the sheared specimen to failure, evidencing a thermally induced failure. Steady state radial permeability tests performed at various stages of the test demonstrated that the overall permeability of the sheared specimen was comparable to that before shearing, confirming the excellent self-sealing properties of the Callovo-Oxfordian claystone. This shows that, in spite of being possibly remobilised by temperature elevation, the EDZ will keep an overall permeability constant equal to that of the massive rock, keeping the same isolation properties.

International audience; Soil structure, especially the soil pore size distribution, is a fundamental property that describes the hydro-mechanical behavior of soils. The volume change behavior, shear strength, water retention capacity and hydraulic conductivity of soil are controlled by the pore size distribution. However, research on soil structure has been limited due to the associated expenses and specialized instruments, such as environmental scanning electron microscopes and mercury intrusion porosimeters (MIPs). In this study, the relationship between the soil water retention curve (WRC) along a drying path and the pore size distribution obtained through an MIP method was reviewed. The WRC for a compacted tropical soil was converted into a soil air injection curve and then used to estimate the pore size density (PSD) function. Relative to the data collected from MIP methods, the results showed an acceptable prediction of the PSD function based on a soil air injection curve. Finally, a series of adjustments to the air injection curve were performed to improve the accuracy of the PSD prediction based on the water retention curve.

International audience; Pile design is not only based on the assessment of bearing capacity, but can involve settlement calculations when the structures supported by piles need high service requirements. In this context, the load transfer approach with t–z curve models is one of the calculation methods used. The main issue for this method is the choice and implementation of the t–z curve modelling the behaviour of the soil around the pile and accounting for the progressive shaft friction mobilisation. In this paper, three types of t–z curve models from pressuremeter test results are compared: one proposed previously by R. Frank and S. R. Zhao in 1982 and two others presented here. The stiffness of each model is studied and a comparison is performed by considering 90 full-scale static load tests extracted from the IFSTTAR pile database. Measured and calculated values of the pile head displacement are compared for several loading levels considering different soil and pile types. For the three t–z curve models, the ratio of the measured pile head settlement value to the calculated one is analysed and the scatter of each t–z curve model is studied. Some considerations regarding the safety of the pile settlement calculations are proposed.

International audience; An experimental study was conducted to investigate changes of thermal conductivity, suction and microstructure of a lime-treated silty soil during curing. The soil samples were prepared with 2% lime and compacted dry (17%) and wet (22%) of optimum. The thermal conductivity, total suction and pore size distribution were determined at various curing times. Results show that the thermal conductivity of samples compacted on the dry side decreases slightly with curing time, while the curing time effect on the samples compacted on the wet side is insignificant. The total suction generally increases with curing time even though the soil water content was kept constant. The pore size distribution characteristics are mainly related to its moulding water content. As the samples are compacted on the dry side, the pore size distribution shows typical bi-modal characteristics, with a population of macro-pores and a population of micro-pores. By contrast, as the samples are compacted on the wet side, the pore size distribution shows typical uni-modal characteristics. It is found that the modal size of both the large and small pores decrease with curing time.

International audience; The mechanical behaviour of an energy pile in saturated clay under thermo-mechanical loading was studied using a model pile. Axial load was first applied to the pile head in steps to determine the resistance of the pile under mechanical load. Afterwards, thermo-mechanical tests were performed by applying a heating/cooling cycle to the pile under constant axial load. The results show pile head heave during heating and settlement during cooling. Irreversible settlement was observed after the thermal cycles. Tests performed with various axial loads show that the thermal irreversible settlement is greater under a higher axial load.

International audience; Infiltration column is usually used to investigate the hydro-mechanical processes in unsaturated expansive clay. In this test, the moisture transfer is often monitored along the column during water infiltration using suction or water content probes. Nevertheless, the lateral swelling pressure developed is rarely considered. This paper describes an infiltration column for studying the lateral swell behavior of expansive clay. The column consists of a rigid cell ensuring the constant-volume condition and a hydraulic system enabling the water intake of the hosted sample. It is equipped with three types of sensors: pressure sensors, force transducers, and displacement transducers to, respectively, monitor the radial and axial swelling pressure of the sample at different positions and to check whether any axial displacement is taking place. A detailed description of the different parts of the cell is first presented. Second, analysis on the results of a test on a compacted bentonite/sand mixture allows the pertinence of such a device to be evaluated.