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The good capacity of the numerical simulations makes possible to bring some further responses on the backfill soil selection and its installation depth in the Horizontal Ground Heat Exchanger (HGHE). Therefore, a well-known backfill soil was considered to be used as substitutive material. The hydrothermal properties of the backfill material were estimated in laboratory and then injected in a numerical framework considering the atmosphere-soil-HGHE interaction. Numerical simulations were performed for a HGHE installed in the compacted backfill soil and the local natural soil. The simulation results showed that the compacted backfill soil improves by 8.5 % the HGHE performance compared to local uncompacted soil. Two heat storage scenarios at three different installation depths were also investigated. The results showed that an inlet fluid temperature of 50 °C in summer increased highly the system performance by 13.7 % –41.4 % , while the improvement was less significant (0 % –4.8 % ) for the ambient inlet temperature scenario. A deeper installation depth of HGHE increased also the system performance, the more energy could be stored and extracted.

International audience; In the context of the French Cigéo-project, a mixture composed of 70% processed Callovo-Oxfordian claystone spoil and 30% MX80-bentonite could be a potential backfill material, whose installation aims to stabilize the surrounding rock formation and to limit the propagation of the excavation damaged zone. The backfill material must sustain the overburden pressure, despite that it might be exposed to different hydraulic and mechanical paths. The reference concept considers employing conventional compaction techniques, although their employment involves spatial variations in the dry density after compaction. In general, as the initial dry density has a significant impact on the hydro-mechanical behavior of backfill materials, it is of major importance to relate the variations in the initial dry density to differences in the behavior. This experimental laboratory study aimed to analyze how variations in the initial dry density affect the swelling and compression behavior of the claystone/bentonite mixture, in particular in unsaturated state. Further, it evaluated whether those variations affected possible hydro-mechanical path dependences. The experimental program comprised suction-controlled oedometer and constant-volume swelling pressure experiments, in which samples characterized by different initial dry densities were exposed to different hydro-mechanical paths. The analysis of microstructural and water retention characteristics complemented the program. Major results indicated that the magnitude of swelling pressure at a given suction depends considerably on the initial dry density, but it is independent of the imposed hydro-mechanical path. Interestingly, the dependency of the yield behavior on the hydro-mechanical path appears to be more pronounced as the initial dry density increases.

International audience; Recent technological advances in the field of heat pumps made it possible to propose new solutions for heating and cooling buildings. Energy geostructures consist in incorporating heat exchangers into buried elements of geotechnical structures. However, the heat exchange leads to a cyclic evolution of the adjacent ground temperature. Thus, many questions arise about the effect of these temperature variations on the hydromechanical parameters of the soil. These issues are important since energy geostructures combine the function of heat exchanger with the bearing or/and retaining functions. In this study, mini-pressuremeter tests were conducted in laboratory on a homogeneous material submitted to different thermal loadings (in the range of 1 to 40 °C). The tested material, an illitic soil, is compacted at its Proctor optimal water content 31.3% and to 90% of its maximal dry density (1.29 Mg/m 3 ) in a 0.6 m diameter and 0.8 m height thermo-regulated container. Six tests are performed in each container in different steps of temperature variations. A decrease in creep pressure and limit pressure with increasing temperature was observed. The first cycle induced more important parameter variations than the subsequent cycles especially for the creep pressure that tends towards a constant value. The limit pressure however, remains dependent to temperature variations beyond the first cycle.; Les récentes avancées technologiques dans le domaine des pompes à chaleurs ont permis de proposer des solutions nouvelles pour le chauffage et le refroidissement des ouvrages. Les géostructures énergétiques consistent à incorporer des échangeurs thermiques dans les éléments enterrés des ouvrages géotechniques. Cependant, l’échange de chaleur conduit à une évolution cyclique de la température du sol adjacent. Ainsi, de nombreuses questions se posent sur l’effet de ces variations de température sur les paramètres hydromécaniques des sols. Ces questions sont importantes puisque les géostructures énergétiques cumulent la fonction d’échangeur thermique et la fonction de portance ou de soutènement. Dans cette étude, quatre massifs de sol ont été compactés dans une cuve de 0,6 m de diamètre et 0,8 m de haut qui est thermo-régulée (1 à 40 °C). Le matériau testé est une argile (illite) compactée à sa teneur en eau optimale soit 31,3 % (essai Proctor normal), et à 90 % de sa masse volumique sèche maximale, soit 1,29 Mg/m 3 . Six essais mini-pressiométriques ont été réalisés dans chaque massif à différentes étapes des sollicitations thermiques appliquées. Les résultats montrent une diminution de la pression limite avec l’augmentation de la température. L’application de plusieurs cycles montre que le 1 er cycle a un impact prépondérant par rapport aux cycles suivants en particulier, pour la pression de fluage qui tend vers une valeur d’équilibre. En revanche, la pression limite conserve sa dépendance à la température au-delà du 1 er cycle.

This laboratory experimental program investigated the impact of variations in the expansive mineral content, the grain size distribution of employed bentonite, the initial dry density and the selected hydration path on the water retention characteristics and swelling properties of processed Callovo-Oxfordian claystone and its mixtures with MX80 bentonite. The French reference concept for the disposal of nuclear waste in deep sedimentary rock formations envisages the reemployment of excavated material as backfill material, which is installed in situ by means of conventional compaction techniques. The investigations were of special interest as the major issues involving in situ compacted backfill materials were portrayed. Experiments showed that the impact of variations in the dry density on the water retention characteristics of all materials vanished as suctions exceeded 100 MPa. The negligible impact of variations in the initial dry density on the collapse behavior of claystone/ bentonite mixtures remained questionable.

The positive effects of lime or cement treatment could be altered by weathering in the very long term. In this context, the main purpose of this study is to examine the impact of wetting/drying cycles on the strength and the hydraulic conductivity of a compacted soil treated with lime and cement. Compacted specimens were cured for 90 days before being exposed up to twelve wetting and drying cycles. A special concern of the study was the experimental method to impose the wetting and drying cycles. Two protocols were employed: one relied on relative humidity control to dry the samples, while the other was based on oven drying. The impact of the cycles was quantified by comparing the performance of the samples exposed to the cycles to the performance of the unsolicited samples. The results showed that the cycles induced a major alteration of the strength of the samples, with both methods. This degradation is associated to a significant increase of the hydraulic conductivity of the samples with the number of cycles.

The incorporation of heat exchangers into geostructures leads to changes in the temperature of the adjacent soil, which may affect its hydro-mechanical properties. In this study, mini-pressiometer tests were carried out in the vicinity of three experimental energy piles of 12 meters length and 0.52-meter diameter installed in saturated sandy soil. Tests were carried out in three locations and in two different depths (namely 3 and 4 meters in depth) before and after cyclic variations of their temperature. The pressuremeter parameters are the pressuremeter modulus EM, the limit pressure PL and the creep-pressure Pf. These parameters characterize the properties of the soils; some measurements were done close to the energy piles (1.25 meters from the center of the pile) using a mini-pressuremeter cell (380 mm in height and 28 mm in diameter). The comparison of the results before and after the four warming-cooling cycles (8° to 19° C) showed a thin thickening of the material at 3 meters depth. These results are coherent with in-lab measurements and with the results of the pile loading tests carried out later on the same site.

Thermal energy storage in embankments can be considered a new economically efficient and environmentally friendly technology in geotechnical engineering. In these structures, horizontal heat exchanger loops can be installed inside different layers of compacted soil to store heat in the medium during the summer to be extracted during the winter. Compacted soils are usually unsaturated; therefore, reliable estimates and measurements of unsaturated compacted soil thermal properties, such as the volumetric heat capacity, thermal conductivity, and thermal diffusivity, are important in the efficiency analysis of these structures. However, there is no available method to characterize the evolution of these parameters over time in compacted soil. In this study, several temperature sensors were placed inside different layers of unsaturated compacted soil in a cylindrical container (height of 0.8 m and diameter of 0.6 m ) to monitor imposed temperature cycle variations. An inverse analytical model based on the one-dimensional radial heat conduction equation is proposed to estimate the thermal diffusivity using the temperature variation between two temperature sensors. The volumetric heat capacity was measured with a calorimeter in the laboratory, enabling estimation of the thermal conductivity of the compacted soil. Then, this estimated thermal conductivity was compared with the thermal conductivity values measured with two different methods (one steady-state and one transient-state method). The estimated thermal conductivity was close to the value measured with the transient-state method. It was demonstrated that steady-state methods are not suitable for the measurement of thermal conductivities as high as 2.5 W . m - 1 . K - 1 since thermal contact resistances are no longer negligible.

International audience; The determination of the shear strength of coarse-grained soils in standard shear devices is a challenging task due to the presence of large grains. Three approaches could be used to reduce the grain size of the tested specimen. This study aimed to determine whether the shear strength of a coarse-grained soil with fines (particles smaller than 0.08 mm) can be estimated by the parallel gradation approach. Direct shear tests were conducted on parallel graded specimens of two soil types with different low plastic fines content. Two criteria can be used to select the dry density of the reconstituted specimen: the same dry density or the same relative density as the initial soil. The results showed that when the specimens had a low fines content, both criteria resulted in a similar dry density of the reconstituted soil, and the shear strength of the initial soil was correctly estimated. However, for the specimens with a high fines content, the friction angle of the initial soil was correctly estimated, and its cohesion was overestimated when the reconstituted soil was tested at the same dry density as the initial soil. A cohesion-fines content relationship was proposed to predict the initial soil cohesion.

The shaft capacity of foundations highly depends on the monotonic and cyclic loads applied to the soil–structure interface. In energy geostructures that exploit the heat of soil using earth...

This study intends to examine the impact of successive wetting and drying cycles on the strength and hydraulic conductivity of lime- and cement-treated soil, with a special emphasis on the ...

International audience; The determination of the mechanical properties of soils containing particles larger than the allowable size of standard laboratory equipments is complex. It is indeed necessary to remove the coarsest fraction to carry out the tests. This scalping poses a problem of reliability of the results at the scale of the structure. Parallel gradation is the method commonly used for estimating the shear strength of heterogeneous granular soils from tests on their finer fraction. However, the effect of high fines content on the estimation of shear strength by this method is not well understood. The results of this study showed that the parallel gradation method could predict the friction angle of the initial soil with high fines content when the modelled soil had a similar skeleton as the initial soil. However, the cohesion of the initial soil was overestimated.

Mixtures composed of 70% crushed Callovo-Oxfordian claystone and 30% MX80-bentonite are considered as materials, that could be used for backfilling a future radioactive waste repository in deep sedimentary rock formations. Their characterization is of interest, as the replacement of fractions of crushed claystone by bentonite enhances the chemo-hydro-mechanical performance of backfill. The materials are envisaged to be installed directly in the drifts and shafts by means of conventional compaction techniques. The hydro-mechanical behavior of materials containing expansive mineral phases, and especially their swelling behavior, is known to be significantly affected by the initial material properties and environmental and stress conditions. The present study aimed to assess the combined impact of variations in the material properties and environmental conditions, particularly the grain size distribution, dry density and saturating solution chemistry, on the swelling pressure of the mixtures, by conducting a comprehensive laboratory experimental program. The results revealed that the adjustment of the grain size distribution of employed bentonite enhanced the compaction behavior and, in turn, the swelling behavior of the mixtures. Generally, swelling pressures of mixtures were less affected by the employed saline and alkaline solutions than those of crushed claystone. The measured swelling pressures were exponentially related to the initial dry density of the expansive mineral phase, regardless of the grain size distribution. Based upon the finding that the expansive mineral phase being present in crushed claystone contributed to measured swelling pressures, a new approach was introduced to calculate the dry density of the expansive mineral phase in bentonites and their mixtures with non-expansive or less-expansive materials.

International audience; The mechanical behaviour of the soil-structure interface plays a major role in the shear characteristics and bearing capacity of foundations. In thermo-active structures, due to non-isothermal conditions, the interface behaviour becomes more complex. The objective of this study is to investigate the effects of temperature variations on the mechanical behaviour of soils and soil-structure interface. Constant normal load (CNL) and constant normal stiffness (CNS) tests were performed on soil and soil-structure interface in a direct shear device at temperatures of 5, 22 and 60 o C. Kaolin clay was used as proxy for clayey soils. The results showed that, in clay samples the temperature increase, increased the cohesion and consequently the shear strength, due to thermal contraction during heating. The temperature rise had less impact on the shear strength in the case of the clay-structure interface than in the clay samples. The adhesion of the clay-structure interface, is less than the cohesion of the clay samples.

International audience

L’objectif principal de ce travail est d’étudier l’impact des traitements au ciment, à la chaux ou avec des argiles, des sols compactés sur leurs caractéristiques d’érosion interne. Un nouveau dispositif d’étude de l’érosion interne modifié et amélioré a été conçu pour quantifier les effets de différents traitements sur l’évolution de la résistance à l’érosion interne du limon de Saint-Quentin compacté. Les résultats montrent que l’impact des différents traitements sur les caractéristiques d’érosion de ce limon se traduit principalement par une augmentation de la contrainte critique. Cette augmentation est plus grande avec l’augmentation du dosage, et dans le cas du traitement au ciment. De plus, pour les traitements avec la chaux et le ciment, la contrainte critique tend à augmenter avec le temps de cure. Par ailleurs, le coefficient d’érosion est affecté uniquement par le traitement à la bentonite dans le cas d’utilisation d’un grand dosage de traitement.

Clayey soils could be exposed to thermal cycles in some engineering applications such as geothermal piles and nuclear waste storages. These temperature changes could affect the consolidation behaviour of these soils. In this context, this paper investigates the impact of temperature on the consolidation behaviour of saturated compacted clays. A temperature-controlled oedometric cell has been developed to perform constant rate of strain (CRS) consolidation tests for different strain rates (0.002 – 0.02%/min) within a temperature range of 5 °C – 70 °C. Two different compacted saturated clays were used in these tests. The results indicated that the compression and swelling indices for both materials changed with temperature and strain rate. The preconsolidation pressure of both clays decreased as the temperature increased, while it decreased as the strain rate decreased. The creep index increased as the temperature increased for both clays. These variations were completely dependent on the nature of ...

International audience; The impact of temperature on the creep deformation of compacted clayey soils is a major issue in the prediction of thevery long term settlement of soils used as engineered barriers for the disposal of high and long-life radioactive wastes at great depth.This paper is focused on the creep behavior of two compacted materials, illite and a swelling clayey soil, as a function of temperatureand suction. Specific temperature controlled oedometric cells have been developed to perform constant rate of strain (CRS)consolidation tests under different strain rates (0.002%/min to 0.02%/min) within a temperature range of 5 to 70° C. Results indicatedthat the compression and swelling indices could be considered independent of temperature and strain rate with both materials. Withtemperature increase, the preconsolidation pressure decreased, and creep index increased. This can be related to a soil softeningbehavior under high temperatures.; Influence de la température sur le fluage d'une argile compactée Temperature effect on the creep behaviour of a compacted clay RÉSUMÉ : L'étude de l'influence des variations de température sur le comportement au fluage des sols compactés argileux est indispensable pour la prédiction des tassements et des déformations des dispositifs d'enfouissement des déchets radioactifs à très long terme. Ce travail est axé sur la compressibilité et le fluage de deux sols compactés : une illite et un sol argileux gonflant. L'impact de la température et de la succion sur les caractéristiques de compactage a été évalué. Cet article présente les résultats d'une campagne d'essais de compression à vitesse de déformation constant (CRS) effectuée dans des cellules oedométriques à température contrôlée. Différentes valeurs de vitesse de déformation allant de 0,002%/min à 0,02%/min ont été appliquées, dans une gamme de température comprise entre 5 et 70°C. Les résultats ont montré que les indices de compression et de gonflement sont peu sensibles à une variation de la température, cette observation étant valable pour les deux sols compactés utilisés. L'augmentation de température entraîne en revanche une baisse de la pression de préconsolidation et une augmentation significative de l'indice de fluage.

International audience; This study is focused on the hydromechanical behaviour of a compacted swelling clay upon wetting. More precisely, a multi-scale investigation of the swelling behaviour of a purified bentonite under constrained conditions was carried out by a monitoring of the swelling pressure and the porosity evolution at various scales (inter-aggregate, inter-particle, interlayer). A specific oedo-tomometer, has been designed to monitor both the swelling pressure and the inter-aggregate porosity evolution deduced from microfocus X-ray computed tomography measurements (size higher than 5 µm). The results showed the influence of hydration on specimens with an increase of the swelling pressure and a decrease of the inter-aggregate pore size during hydration. Therefore, a coupling between swelling pressure and textural reorganisation at inter-aggregate pore scale was highlighted. This coupling was also based on hydration process at interlayer scale.; L'hydratation d'une argile gonflante provoque une augmentation de sa pression de gonflement associée à une réorganisation profonde de sa microstructure à toutes les échelles. L'objectif de ce travail est de caractériser et de comprendre les processus couplés chémo-hydromécaniques multi-échelles dans les argiles soumises à la circulation d'un fluide. Un dispositif spécifique, oedo-tomomètre, a été conçu pour assurer le suivi couplé de la pression de gonflement en corrélation avec l'évolution de la porosité inter-agrégat identifiable par microtomographie de rayons X (taille > 5 µm). Les résultats ont permis d'établir une corrélation entre le développement de la pression de gonflement et la réorganisation progressive de la porosité d'une argile gonflante compactée. L'utilisation de différents fluides a permis de montrer le couplage entre l'évolution de la pression de gonflement et la réorganisation de la porosité inter-agrégats, couplage lui-même dépendant des processus d'hydratation induits à l'échelle interfoliaire (gonflement cristallin ou osmotique).

International audience; Sustainable development principles are leading earthwork companies to use all-natural materials extracted from the construction site to build the infrastructure. Natural materials with low characteristics must be improved. For dry soils, the common solution is to increase the compaction energy or add important quantities of water to reach the target dry density and bearing capacity. To reduce the environmental impact of their activities, the use of industrial organic products has been proposed. The aim of this study was to assess the potential benefits that could be expected from the use of these non-traditional treatments in earthworks with a well-recognised environmental impact assessment methodology.

La mise en place de méthodes permettant d’emmagasiner la chaleur dans le sol engendre des questionnements sur l’impact des variations de températures sur les propriétés thermiques des matériaux et sur la possibilité d’optimiser l’efficacité de ces procédés dans le cas où le massif de stockage est anthropique (sols compactés). En effet, à proximité des échangeurs, la modification de la température pourrait provoquer une évolution du volume des constituants des sols et des propriétés d’écoulement de l’eau, ce qui pourrait engendrer une variation des propriétés thermiques du matériau. Dans cette étude, des essais sont réalisés afin de quantifier l’effet couplé de la teneur en eau (w), de la densité sèche et de latempérature (T) sur les paramètres thermiques de différents sols compactés argileux ou limoneux. Pour les 5 matériaux testés, les résultats montrent une augmentation de la conductivité thermique du côté sec de la courbe de compactage jusqu'à atteindre un maximum aux alentours de l’optimum Proctor. Les capacités thermiques calorifiquesmesurées (C) évoluent dans le même intervalle de variation pour les 5 matériaux malgré leur différence de minéralogie et de texture. Enfin, la diffusivité thermique suit la même évolution que lambda .Les résultats montrent une augmentation des propriétés thermiques avec l’augmentation de la température, plus particulièrement marqué dans l’intervalle 40-70 °C. Cette augmentation est plus importante pour les éprouvettes compactées du côté sec de la courbe de compactage., Academic Journal of Civil Engineering, Vol 34 No 1 (2016): Special Issue - RUGC 2016 Liège

International audience; A specific oedometer cell has been set up to measure the swelling pressure of compacted montmorillonites at constant volume and to concomitantly visualise the evolution, upon wetting, of how the microstructure is organised through X-ray microtomography. The swelling pressure experiments were conducted with solvents of various natures. In addition to conventionally used water and saline solutions, we used an organic solvent (methyl methacrylate – MMA). We chose this to explore the effect of its different physical and chemical properties, and to differentiate the respective roles of crystalline and osmotic pressures on macroscopic swelling behaviour.The results, which combined both swelling pressure measurements and quantification of microstructure evolution upon hydration for the two different solutes, give sound understanding on the development of osmotic and/or crystalline swelling and their relative impact both on the microstructure and on the magnitude of the macroscopic swelling pressure of compacted montmorillonites.

International audience; The paper reports results of an experimental study focused on the investigation of the development of swelling pressure in compacted bentonites during wetting under confined conditions. The main swelling pressure testing program has been performed using a new constant-volume oedometer especially designed to apply suction using the osmotic method. The device allows to continue to determine swelling pressure under constant-volume conditions during wetting close to saturation (suction below 8.5 MPa). Constant-volume swelling pressure tests were performed by decreasing the suction (or increasing the humidity) of the specimens from almost 100 MPa to 8.5 MPa and then in stepwise manner toward a zero value. In addition, a series of swelling pressure tests were performed using different experimental devices to compare test results obtained using the new device and to investigate the effect of hydration mode on the swelling pressure of compacted bentonites.Different wetting modes, water or vapor wetting, resulted different equilibrium swelling pressure values. Three stages of swelling pressure development are identified during suction reduction. In the first stage, following large suction reduction, swelling pressure increases up to a peak value; then, in second stage, in suction range comprised between 8.5 and 3.5 MPa, swelling pressure tends to decrease to a minimum value; and finally, upon further suction reduction to low values, swelling pressure increases again and eventually stabilizes. A possible interpretation of this pattern is given from micro-structural perspective.

Energetic geostructures consist in establishing a thermal exchange with the ground directly through systems integrated into the building foundations or structures. Incorporation of heat exchangers into geostructures brings questions on the impact of the temperature variations on the geotechnical parameters of the sensitive soils (illite, smectite...). The design of the bearing capacities of deep foundations is actually based on pressuremeter or penetrometer test results. In this study, a mini-pressuremeter test was developed to carry out laboratory tests on compacted samples submitted to different thermal variations. Mini-pressuremeter tests were conducted on an illitic soil compacted in a cylindrical container, submitted to temperature equal to 1, 20 and 40 °C. The impact of the temperature variation on the limit pressure (pl) and the creep pressure (pf) is presented.

International audience; The effect of lime on the yield stress, and more generally the presence of structure in the soil, is usually not accounted for in the design of geotechnical structures. As a result the potential of lime treatment or of a structured soil has not been fully exploited. This paper presents a new formulation to account for the effect of structure on the mechanical behaviour for structured soils. A constitutive model is proposed in the framework of the Modified Cam Clay model to describe the behaviour of lime treated soils. The new formulation introduces a limited number of additional parameters, all of which have a physical meaning and can be obtained from an isotropic compression test. Due to similarity in behaviour of lime treated soils and naturally structured soils, the formulation can be applied to both types of soil. It is shown that the proposed model can successfully reproduce the main features of both structured soils such as maximum rate of dilation at softening and degradation at yield. The model can be applied for any structured material regardless of the origin of cementation.

International audience; The main purpose of this paper is to examine the impact of a wetting and drying path on the swelling/shrinkage of a compacted lime-treated expansive clayey soil both at the macro- and micro-scales. At the macro-scale, the soil water characteristic curves (SWRCs) of the compacted lime-treated materials (0%, 2% and 5% of lime content) were determined for three curing times (0, 28 and 180 days). The modifications at the micro-scale were assessed with mercury intrusion porosimetry (MIP) tests. The results showed that lime treatment was efficient to prevent the volumetric swelling from the initial state upon wetting. Even if no significant macroscopic volumetric variation was observed, a reorganisation of the microstructure was evidenced. Upon drying, the lime addition led to an alteration of the hydro-mechanical soil behaviour from the initial state by increasing the compacted shrinkage limit suction. However, the volumetric shrinkage of the compacted lime-treated samples remained on the same order of magnitude of the untreated compacted soil, regardless of lime content and curing time. At the micro-scale, the \MIP\ tests showed that drying altered both the macro- and micro-porosity fabric of the lime-treated soils. This study showed that lime treatment had a limited effect on lime-treated compacted soil shrinkage whilst preventing swelling.

International audience; The positive effects of lime treatment are likely to be altered by weathering, and the sustainability of lime-treatment positive effects is in question. In this study, the effects of successive drying/wetting cycles on the hydromechanical properties of a lime-treated clayey soil are assessed. Osmotic suction-controlled oedometers were used to determine the swelling/shrinkage behavior of soils subjected to successive drying/wetting cycles of small amplitude. Significant degradation of the yield stress was observed while the efficiency of the treatment on volumetric behavior remained unchanged, this being related to the stabilization process. This study showed that the evaluation of the mechanical sustainability of a lime-treated material subjected to wetting and drying cycles requires tests in realistic conditions.

International audience; Lime treatment has been widely used to improve mechanical properties of soils. However, less has been done to account for the effect of the treatment on constitutive relationships. In this study, a comprehensive programme of isotropic consolidation tests and drained triaxial experiments were designed and carried out on saturated specimens of a silt treated with quicklime. The chemical composition in hydrates, portlandite, and carbonates was determined using thermogravimetric analysis and differential thermal analysis. The modifications to the mechanical parameters of the soil were evaluated in the framework of the Cam Clay elastoplastic model. The experimental results revealed that the addition of lime leads to the modification of the critical state. For concentrations in lime higher than 1%, the treated specimens displayed a different normal compression line compared to the untreated state. Chemical analysis revealed the production of cementitious compounds for every concentration tested. A constitutive model was proposed to describe the observed behaviour of lime treated soils in the framework of the Structured Cam Clay. The model accounts for the modifications on the mechanical parameters of the soil. A chemo-mechanical coupling was established between the yield stress and the mass concentration in cementitious compounds.

International audience; The aim of this study was to characterise the technical and environmental implications of non-traditional treatments of a low-plasticity compacted silt (PI = 14) and to investigate their actions both at the micro- and macro-structural scales. Three non-traditional additives derived from industrial vegetal by-products were studied. These additives are classified as an acid solution, an enzymatic solution (ES) and calcium lignosulfonate (LS). The first step was to characterise the effects of these treatments on Proctor compaction, bearing capacity, unconfined compressive strength and stiffness. The index properties of the treated samples were also measured to assess changes in the interaction between soil minerals and the additives. These experimental results showed that the 0.002 % ES and 2.0 % LS treatments were the most effective at improving the soil dry density and allowing the soil to reach optimum density using 3 % less water or 25 % less compaction energy. In a second step, the mechanisms involved in the treatment were investigated. A microscopic study was conducted including scanning electron microscopy and mercury injection porosity tests; measurements of the surface tension of non-traditional additives mixed with water completed the study and demonstrated that the ES treatment has the same surfactant properties as sodium dodecyl sulphate, a common surfactant. Compaction tests confirmed that the behaviours of the soil after ES and sodium dodecyl sulphate treatments were similar.

International audience; Lime treatment induces several time-dependent physico-chemical processes (cation exchange, pozzolanic reactions, etc.) that result in the bonding of soil particles. This treatment can reduce the swelling properties of clays and improve their strength. Nevertheless, these positive effects of lime-treatment could be altered by weathering in the very long term. In this paper, the effects of successive drying/wetting cycles on the hydro-mechanical properties of a lime-treated clayey soil are considered. Quicklime-treated samples were subjected to successive controlled-suction (osmotic technique) drying/wetting cycles; and also severe hydric cycles corresponding to an alternation of oven drying and saturation. The effect of quicklime dosage and curing time were considered. The results show a progressive increase of the swelling properties of the material and a progressive loss of strength with increasing number of drying/wetting cycles. The extent of the degradation is directly related to the amount of added quicklime and the amplitude of the suction cycles. Mercury intrusion porosimetry tests show that successive cycles lead to a progressive change of the micro-fabric, thus explaining partly the degradation of macroscopic properties. This study shows that weathering by successive drying/wetting cycles is likely to significantly alter the properties of a lime-treated soil, thus weathering effects should be accounted for the long term design of treated soil structure.

Sustainable development principles lead earthworks companies to use all natural extracted materials on the construction site. Most of the time, these materials have to be improved, lime and cement being the traditional additives. In this context, the use of organic by products from various industries has been proposed. But the effects of these non-traditional additives on soil behaviour and stabilizing mechanisms are not well understood. The aim of this paper is to characterize the modification of compaction and bearing capacity of a low plastic soil (Plasticity index PI = 14) and to propose a stabilization mechanism. In this study, three non-traditional products were tested: an acid solution, an enzymatic solution and a calcium lignosulfonate powder. For the enzymatic, and lignosulfonate treatments, the experimental results showed an increase in the compaction ability of the selected soil with a reduction in optimum Proctor water content. These effects induced potential water and energy savings for the compaction of dry soils on a construction site. Regarding the stabilisation mechanisms, the obtained results showed that the effects of non-traditional products are mainly related to their surfactant features.

International audience

International audience; When subjected to a very high-pH, most of the soil minerals undergo physico-chemical transformation. This could induce strong modifications of the shear strength behaviour of the soil. This issue is of high interest in the framework of the design of deep nuclear wastes repositories, since the degradation of the concrete lining of deep galleries after thousands of years will generate an alkaline solute (pH > 12) that would circulate through the backfill, and alter its hydromechanical characteristics. A study was undertaken to assess the impact of high-pH fluid circulation on the shear strength behaviour of a backfill material. Because of the complexity of the existing constitutive theories, a new approach was used, based on evolutionary polynomial regression (EPR), for modelling of these processes. \EPR\ is an evolutionary data mining technique that generates a transparent and structured representation of the behaviour of a system directly from data. An \EPR\ model was developed and validated using results from a comprehensive set of triaxial tests. Through a sensitivity analysis, the \EPR\ model permitted to identify the specific surface, and to a lesser extent the micropore void ratio, as coupling parameters between hydromechanical behaviour alteration during alkaline fluid circulation and a physical process.

International audience; To better understand the hydro-mechanical behavior of dual porosity expansive clays, three groups of tests were carried out. First, isotropic free drying and free wetting tests were performed to determine both branches of the soil water retention curve of a silt–bentonite mixture and its parameters. Next, constant suction oedometer tests at different matric suctions were employed using osmotic method. Finally, wetting–drying cycles were imposed on the samples in oedometric condition. At the end of wetting–drying tests, different suction values were enforced on the specimens and consolidation tests were performed, while the suction values were regulated through the samples using the osmotic method. Cross-examination of results indicates good consistency between the observed behaviors from different tests: Results of constant suction oedometer tests confirm the hardening phenomenon at low suctions indicated by the free drying test. Besides, all tests show that the amount of the suction hardening is negligible at suctions between the air entry of macropores and that of the micropores. However, the results contradict the physical models of hydro-mechanical behavior of expansive clays which do not take into account the suction induced hardening in the range of suctions less than the air entry value. Moreover, while most of the models assume that the shrinkage limit and air entry suction are coincident; results of the free drying test show the coincidence of the shrinkage limit and the air entry value of micropores

International audience; The main purpose of this study is to examine both at micro-and macro scales the effects of wetting / drying on swelling / shrinkage behaviour of a com-pacted expansive clayey soil treated with lime. The results showed that lime treatment was efficient to prevent the swelling, but the shrinkage remained unchanged , regardless of the added lime content. Even if no significant volumetric variation was observed upon wetting, a reorganisation of the lime-treated soil mi-crostructure was evidenced. Moreover, an alteration of both micro-and macro-porosity of the lime-treated materials was observed upon drying.

International audience; In the French concept of deep nuclear waste repositories, the galleries should be backfilled with excavated argillite after the site has been filled. Some additives like lime could be used to improve the mechanical characteristics of the argillite. After thousands of years, the degradation of the concrete lining of the galleries will generate an alkaline solution (pH value > 12) that will diffuse through the backfill. This study presents the effect of a saturated Ca(OH) 2 solution circulation through lime-treated sample at 60 °C for 3, 6 and 12 months, respectively. The effect of such circulation on the lime-treated Manois argillite (MA) was assessed by petrographical examination coupled to image analysis and scanning electron microscopy (SEM) equipped with energy dispersive X-ray (EDX) analyser of soil pieces. The objective of this study is to make the link among the mineralogical transformations, the textural and mechanical changes produced in the compacted clayey soil as a consequence of the alkaline solution circulation.

International audience; Cet article rapporte un ensemble de résultats d'études expérimentales effectuées sur un matériau gonflant naturel. Dans un premier temps, un essai de porosimétrie au mercure a mis en évidence la double structure du sol étudié: la micro- et la macrostructure. Afin d'obtenir la courbe de rétention d'eau, deux méthodes d'imposition de succion ont été appliquées: la méthode osmotique pour les succions inférieures à 8,5 MPa et la méthode de solutions salines pour les succions supérieures à 8,5 MPa. Des essais œdomètriques ont également été effectués avec imposition de succion par la méthode osmotique. Plusieurs cycles de séchage―humidification entre 0 et 2 MPa ont été appliqués sur des éprouvettes sous trois faibles charges mécaniques constantes (20, 40 et 60 kPa). Pendant ces cycles, ces éprouvettes présentent un gonflement cumulé. Les résultats montrent que les déformations volumiques convergeant vers un état d'équilibre où le sol présente un comportement réversible. L'ensemble de ces résultats a permis d'obtenir les paramètres du modèle élastoplastique (BExM). Ce modèle implanté dans un code de calcul aux éléments finis (Code_Bright) est utilisé pour l'étude du comportement hydromécanique de ce sol naturel chargé par une semelle filante. L'objectif de cette étude est d'analyser l'influence des sollicitations hydriques sur les déplacements de cette fondation. Le modèle est capable d'aboutir à des résultats représentatifs de ce type de chargement hydromécanique complexe

International audience; In the French concept of deep nuclear wastes repository, the galleries should be backfilled with excavated argillite after the site exploitation period. After several thousands of years, the degradation of the concrete lining of the galleries will generate alkaline solute (pH N 12) that will diffuse through the backfill. The object of the paper is to describe the influence of such solute diffusion on the properties of compacted argillite. Since it is planned to introduce additives (bentonite, calcareous sand or lime) in the remoulded argillite to backfill the deep galleries, such mixtures were also studied. Saturated-portlandite water was circulated through compacted samples for 3, 6 and 12 months at 20 or 60 °C. The microstructure before and after fluid circulation was determined with mercury intrusion porosimetry. The results showed that the 50% sand-50% argillite mixture microstructure was slightly affected by the alkaline fluid circulation. Conversely, the microstructure of the other tested materials changed dramatically. The fluid circulation provoked an increase of the macropore void ratio by almost 3 times for the pure argillite, almost 1.5 for the MX-80 and argillite mixture and 2 for the lime-treated argillite. This particular behaviour could be attributed to the dissolution of soil minerals in such a high pH environment. Hence, it is likely that hydraulic and mechanical properties of these mixtures would be dramatically affected by alkaline solute diffusion over a long period of time.

The swelling properties of a bentonite MX-80 and a Na montmorillonite obtained from MX-80 purification were analyzed as a function of relative humidity in free and constrained conditions. Gravimetric and XRD techniques were used to study the hydration of powder and compacted pellets in non confined conditions whereas hydration under constrained conditions was investigated in situ by neutron diffraction using a cell specifically designed for the present study. MX-80 bentonite and purified montmorillonite were compacted to an apparent density of 1.7 and equilibrated at various relative humidities using P 2 O 5 and solutions saturated with different salts allowing to work in a wide range of relative humidity between 0 and 0.98. At low relative humidity, the hydration of montmorillonite is similar in free and constrained conditions. For relative pressures higher than 50%, swelling in constrained pellets deviates from that observed for free pellets. Reorientation phenomena of clay layers were also observed for bentonite and montmorillonite starting at 65% RH. At 98% RH, two well-defined basal spacings were obtained in the case of confined bentonite. The major peak corresponds to three-layer hydrates (18.6 A) and the second one to two-layer hydrates (16 A). In contrast, only the latter peak is observed when hydration is realized in free geometrical conditions. In the case of Na montmorillonite, for the same relative humidity, the confinement cell did not resist swelling pressure. This was explained by the fact that, for the 1.7 density, porosity was too small to allow the formation of the three layer hydrates to compensate for water swelling pressure.

A study of the hydromechanical behaviour of a compacted swelling material in the range of suctions comprised between 0 and 40 MPa was performed. This study has required the development of two kinds of suction controlled oedometer devices based on two different suction control techniques. In the range of suctions higher than 8.5 MPa, the saturated salt solutions method was used and a new oedometer using this suction control technique was developed. For suctions lower than 8.5 MPa an osmotic oedometer was used. Despite the differences between the applied suction components (matric and total), the correlation between the two methods was verified for the tested material. The second part of the paper presents a set of oedometer tests conducted under various suctions. The effect of the applied suction on the hydromechanical parameters was studied. First, two swelling phases were highlighted: a low swelling phase above a suction of 4 MPa and a high swelling one below this value. These phases were considered as being related to the microstructure of compacted swelling clays. Secondly, it was shown that the slopes of the elastic part and of the plastic part of the consolidation curves were not influenced significantly by the applied suctions. In opposition, the preconsolidation pressure is affected by the decrease of the applied suctions even in the low swelling phase. Such a behaviour could be explained by the effects of wetting on the microstructure.

International audience; aboratory tests on a two-dimensional model of an anchored sheet pile structure are carried out to study the displacement field of a soil-structure system. The comparison of the experimental results with those obtained by the Kranz method shows significant differences. The overall stability analysis of these structures is then investigated by a theoretical model using the upper-bound method of the limit analysis theory. A translational failure mechanism is considered for the calculation scheme. This mechanism is composed of two rigid blocks in the active zone and the so-called log-sandwich mechanism in the passive zone. Numerical results show good agreement with results obtained from laboratory tests.; Des essais de laboratoire sur un modèle réduit bidimensionnel ont été effectués afin d'étudier le champ de déplacement d'un soutènement ancré. Une confrontation critique des résultats du modèle réduit aux approches de type Kranz nous conduit à proposer un autre schéma de calcul basé sur la théorie de l'analyse limite en considérant un mécanisme de rupture translationnel. Ce mécanisme est composé de deux blocs rigides dans la zone active et d'un mécanisme de rupture en «log-sandwich» dans la zone passive. La confrontation des résultats numériques avec ceux des expériences réalisées montre la pertinence du mécanisme adopté.

The use of compacted swelling soils in engineering practice is very widely spread, especially in geotechnical and environmental engineering. After their setup, these materials are likely to be subject to complex suction/stress paths involving significant variations of their hydro-mechanical properties which can affect their initial behaviour. It is important to be able to predict the hydromechanical behaviour of these materials taking into account the significant applications for which they are intended.Barcelona team developed a finite-element code (Code_Bright) for the thermo-hydro-mechanical coupling (THM) integrating the BBM elastoplastic model for unsaturated soils based on the independent variables approach. This model is recognized to correctly describe the hydromechanical behaviour of unsaturated soils but fails to take into account some particular observed aspects on swelling soils. A second model BExM was then proposed to address these aspects. The objectif of this study is: (i) to implement the elastoplastic model BExM for the unsaturated swelling soils in the finite-element code (Code_Bright); (ii) to check the numerical model validity through the numerical simulation of laboratory tests made on swelling soils; and (iii) to apply this model to some practical problems. For this purpose, a new family of numerical procedures adapted to the BExM model was introduced into the code. The equation of the yield surface of this model for a given deviatoric stress states was given in a manner to facilitate calculations of its derivatives. The model was checked by the numerical simulation of suction-controlled œdometric tests made on three different swelling soils. The simulation results showed that the numerical model is able to correctly reproduce the experimental data. Lastly, the model was applied to two practical problems: radioactive waste repository in deep geological layers and a shallow footing under the action of a swelling soil. The results obtained showed the ability of the numerical model to modeling hydromechanical coupled problems., Les sols gonflants compactés sont largement utilisés dans de nombreuses applications, notamment en géotechnique et en géotechnique de l'environnement. Après leur mise en place, ces matériaux risquent d'être soumis à des sollicitations hydriques et/ou mécaniques complexes qui peuvent entraîner de fortes modifications de leurs propriétés hydromécaniques susceptibles de mettre en cause leur fonctionnement initial. Il est donc important de prévoir le comportement hydromécanique de ces matériaux compte tenu des applications sensibles auxquelles ils sont destinés.L'équipe de Barcelone a développé un code de calcul aux éléments finis (Code_Bright) pour l'analyse des problèmes couplés (THM) dans des géomatériaux, avec l'intégration du modèle élastoplastique (BBM) pour les sols non saturés non gonflants. Ce modèle est capable de décrire correctement le comportement hydromécanique des sols non saturés mais ne tient pas compte de quelques aspects particuliers observés sur des sols gonflants. Un deuxième modèle (BExM) a été alors proposé pour prendre en considération ces aspects. L'objectif principal du travail présenté ici est : (i) d'implanter le modèle élastoplastique BExM pour les sols gonflants non saturés dans le code de calcul aux éléments finis Code_Bright ; (ii) de valider le modèle numérique à partir d'essais réalisés au laboratoire sur des sols gonflants ; et (iii) d'appliquer ce modèle aux simulations des problèmes pratiques. Pour atteindre cet objectif, une nouvelle famille de procédures numériques adaptées au modèle BExM a été introduite dans le code. L'équation de la fonction de charge de ce modèle pour un état donné de contrainte déviatorique a été déterminée de manière à faciliter les calculs de ses dérivées. La validation numérique du modèle a été vérifiée par des simulations numériques d'essais œdométriques à succion contrôlée, réalisées sur trois sols gonflants différents. Les résultats des simulations numériques de ces essais ont montré les aptitudes du modèle numérique implanté à reproduire correctement les résultats expérimentaux. Enfin, le modèle a été appliqué à deux problèmes pratiques : le stockage de déchets radioactifs dans les couches géologiques profondes et l'effet du retrait-gonflement du sol sur une fondation superficielle. Les résultats obtenus ont montré la capacité du modèle implanté à modéliser des problèmes couplés hydromécaniques.

In the context of the Cigéo-project, the French agency in charge of radioactive waste manage-ment (Andra) studies claystone-based materials as to whether they can be potentially used to backfill shafts and drifts of the future repository for intermediate - and high-level radioactive waste located in the clay-rich Callovo-Oxfordian (COX) sedimentary rock formation at a depth of around 500 m. The installation of backfill in shafts and drifts generally aims to ensure the integrity of the repository system upon its closure. In particular, it is installed to stabilize the geo-logical formation and to limit the propagation of the damaged/ disturbed zone evolving around the excavations. Potential backfill materials must thus sustain the overburden pressure and ex-hibit swelling pressure when they saturate under constant-volume conditions. In addition, the closure of hydraulic conductive voids ensues through the swelling under con-stant-volume con-ditions. Crushed and sieved COX-claystone spoil and its mixtures with MX80-bentonite are po-tential backfill materials as they contain smectite, which typically exhibits such a hydro-mechanical behavior. On account of the fraction of smectite, potential backfill materials and their hydro-mechanical behavior are affected by different geo-environmental conditions. In this laboratory experimental study, it is of general interest to analyze how variations in geo-environmental conditions affect the performance of potential claystone-based backfill materials, in particular their volume change and hydraulic conductivity behavior. Relevant geo-environmental conditions are the fraction of smectite in the materials, the maximum grain di-ameter of the bentonite fraction in the mixture, the as-compacted/ initial dry density, the degree of saturation, the saturating solution chemistry, in particular its pH, and their combinations. Var-iations in the as-compacted/ initial dry density are expected to be of greatest relevance as con-ventional compaction techniques might be employed to compact the backfill material in-situ. The hydro-mechanical behavior of processed COX-claystone spoil and its mixture with MX80-bentonite are analyzed by means of constant-volume swelling pressure, free-swell potential, one-dimensional compression/ oedometer and constant-head hydraulic conductivity experi-ments. Initially, it is evaluated how the fraction of smectite in the materials, the maxi-mum grain diameter of the bentonite fraction, the initial dry density and the saturating solution chemistry affect individually and combined the evolution of the swelling pressure of claystone-based backfill materials. The individual and combined impact of the fraction of smectite in the materi-als as well as of the saturating solution chemistry on the evolution of the hydraulic conductivity are subsequently assessed. In order to analyze the impact of the pH of solutions, the hydraulic conductivity experiments are complemented by microstructural and textural analysis. The vol-ume change behavior of the processed COX-claystone/ MX80-bentonite-mixture are evaluated not only in the saturated but also in the unsaturated state al-lowing to identify possible hydro-mechanical path dependencies. By considering samples compacted to different initial dry densi-ties, it is assessed whether the initial dry density affects possible dependencies of the volume-change behavior on the hydro-mechanical path. Based on the performed investigations, conclu-sions regarding the hydro-mechanical behavior of claystone-based backfill materials are drawn, and suggestions for future studies are made., Dans le cadre du projet Cigéo, l'agence française chargée de la gestion des déchets radioactifs (Andra) étudie des matériaux à base d'argile qui pourraient être utilisés pour remblayer les puits et les galeries du futur stockage de déchets radioactifs de moyenne et haute activité, situé dans la roche sédimentaire Callovo-Oxfordienne (COX) riche en argile, à une profondeur d'environ 500 m. L'installation de remblai dans les puits et les galeries vise généralement à assurer l'intégrité du système de stockage dès sa fermeture. Il sert à stabiliser la formation géologique et à limiter la propagation de la zone endommagée/perturbée autour des excavations. Les matériaux de remblai potentiels doivent donc supporter la contrainte verticale in situ et montrer une pression de gonflement lorsqu'ils saturent dans des conditions de volume constant, celle-ci provoque la fermeture des vides conducteurs hydrauliques. Les déblais d'argile COX broyés et tamisés et leurs mélanges avec de la bentonite MX80 sont des matériaux de remblai potentiels, car ils contiennent de la smectite qui présente un tel comportement hydromécanique. En raison de la présence de smectite, les matériaux de remblai potentiels et leur comportement hydromécanique sont impactés par différentes conditions géoenvironnementales. Dans cette étude expérimentale en laboratoire, il est judicieux d'analyser comment les variations des conditions géoenvironnementales adéquates affectent la performance des matériaux de remblai potentiels à base d'argile, et plus spécifiquement leur changement de volume et leur comportement de conductivité hydraulique. Les conditions géoenvironnementales pertinentes qui affectent les différents paramètres du remblai, sont la fraction de smectite dans les matériaux, le diamètre de grain maximum de la fraction de bentonite dans le mélange, la densité sèche initiale, le degré de saturation, la chimie de la solution saturante, en particulier son pH, et leurs combinai-sons. Les variations de la densité sèche initiale devraient être les plus importantes car les techniques de compactage conventionnelles pourraient être utilisées pour compacter le matériau de remblai in situ. Le comportement hydromécanique des déblais d'argile COX traités et de leur mélange avec la bentonite MX80 est analysé par le biais des méthodes de pression de gonflement à volume constant, de potentiel de gonflement libre, de compression/ oedomètre unidimensionnel et de conductivité hydraulique à charge hydraulique constante. Dans un premier temps, on évalue comment la fraction de smectite dans les matériaux, le diamètre de grain maximum de la fraction de bentonite, la densité sèche initiale et la chimie de la solution saturante affectent individuellement et conjointement l'évolution de la pression de gonflement des matériaux de remblai à base d’argile. L'impact individuel et combiné de la fraction de smectite, ainsi que celui de la chimie de la solution saturante sur l'évolution de la conductivité hydraulique sont ensuite évalués. Afin d'affiner l'impact du pH des solutions, des analyses microstructurales et de texture viennent compléter les essais de conductivité hydraulique. Puis le comportement des changements de volume du mélange COX-argile/ MX80-bentonite traité est évalué, non seulement à l'état saturé mais aussi à l'état non saturé, ce qui permet d'identifier les éventuelles dépendances des schémas hydromécaniques. Enfin, en considérant des échantillons compactés à différentes densités sèches initiales, il est déterminé si la densité sèche initiale affecte les éventuelles dépendances du comportement de changement de volume sur le chemin hydromécanique. Sur la base des recherches effectuées, des conclusions concernant le comportement hydromécanique des matériaux de remblai à base d'argile sont présentées et des suggestions sont faites pour de futures études.

Nowadays, thermal energy storage in geostructures like embankments can be possible by installing the horizontal heat exchangers in different layers of compacted soil. In this system, the thermal energy is stored in summer via a fluid, circulating in the heat exchangers, to be extracted in the demand period. When the serviceability of embankment as a medium to store the thermal energy starts, the compacted soil will be subjected to the daily and seasonally temperature variations. These seasonal temperature variations could modify the thermo-hydro-mechanical performance of the compacted soil. Thus, the aim of this study is to investigate the thermal and mechanical performances of a compacted soil when it is subjected to monotonic and cyclic temperature variations. The studied soil is a sandy lean clay that is frequently used in embankment constructions in France. The thermal and mechanical behavior of the soil are investigated at a compaction state corresponding to the optimal thermal properties. However, this compacted soil is unsaturated and the estimation of its thermal properties is complex. In this study, an inverse analytical model is proposed to estimate the thermal properties of the soil using temperature monitoring in the range of 20 to 50 °C in a soil compacted in a large container. The estimated thermal parameters were compared to classical laboratory measurements (transient and steady-state methods). The comparison showed that the estimated values were close to the results obtained in transient laboratory method. Using this method, the thermal efficiency of the compacted soil can be verified in the lifetime of the storage system. To ensure the structure stability, long-term mechanical response of these systems subjected to monotonic and cyclic temperature variations should be investigated. To achieve this aim, using temperature-controlled oedometric and direct shear devices, consolidation and shear parameters of the studied soil at different monotonic (5, 20, and 50 °C) and cyclic (5 to 50 °C) temperatures were investigated. The results of temperature-controlled oedometric tests showed that the effect of the temperature variation is more pronounced under vertical pressures higher than the preconsolidation pressure. The compression and swelling indexes could be considered independent of temperature variations. Therefore, the overall settlement of the embankment due to thermal variation near the heat exchangers could be considered negligible. The results of temperature-controlled direct shear tests showed that the temperature variations (monotonic heating or cooling, or temperature cycles) increased the cohesion which is beneficial for the bearing capacity and slope stability of embankments. These results can be directly used in the design of embankments to store thermal energy exposed to similar thermo-mechanical paths. Finally, the thermal performance of the compacted soil is verified using a numerical simulation considering the soil atmosphere interaction. Different depths installation of heat exchanger loops and different heat storage scenarios were simulated. The results showed that the compacted soil increases 8.5% the systems performance compared to the horizontal loop installation in the local soil. The results of two different scenarios show that an inlet fluid temperature of 50 °C in summer increases highly the system performance (13.7% to 41.4%) while the improvement is less significant (0% to 4.8%) for the ambient inlet temperature. Moreover, a deeper installation of horizontal loops increases the system performance. From the numerical simulation results can be concealed that the embankment is in interaction with the atmosphere from its upper and lateral surfaces, the thermal efficiency of the structure could be affected due to heat losses. Therefore, it is preferable to place the heat exchangers away from the top and side surfaces., Le stockage de chaleur dans des géostructures énergétiques telles que des remblais est réalisable en installant des échangeurs horizontaux au sein des différentes couches de sol compacté. Dans ce système, l'énergie thermique qui est injectée en été via un fluide caloporteur circulant dans les échangeurs de chaleur, peut être extraite en période hivernale. Dans ces conditions, lors de la mise en service, le sol compacté est soumis à des variations de température quotidiennes et saisonnières. Ces variations pourraient modifier les performances thermo-hydro-mécaniques du sol compacté. Ainsi, le but de cette étude est d'étudier les performances thermiques et mécaniques d'un sol compacté lorsqu'il est soumis à des variations de température monotones et cycliques. Le sol étudié est un limon fréquemment utilisé dans les constructions de remblais en France. Le comportement thermique et mécanique du sol est étudié à un état de compactage correspondant aux propriétés thermiques optimales. Dans cet état, le sol compacté est non saturé ce qui complexifie l'estimation de ses propriétés thermiques. Pour pallier à ces difficultés, dans cette étude, un modèle inverse est proposé pour estimer les propriétés thermiques du sol compacté. L’efficacité du modèle est testée sur un jeu de données acquises dans la gamme de 20 à 50 °C dans un modèle réduit en laboratoire. Les valeurs obtenues sont ensuite comparées à des mesures classiques en laboratoire (méthodes en régime transitoire et en régime permanent). Cette méthode pourrait permettre de suivre l’évolution des propriétés thermiques du stockage et ainsi assurer son efficacité tout au long de sa durée de vie. La question de la stabilité à long terme de ces structures soumises à des variations thermiques monotones (5, 20 et 50 °C) et cycliques (5 à 50 °C) est ensuite abordée à l'aide d'essais oedomètriques et d’essais de cisaillement direct à température contrôlée. Les résultats des essais de compressibilité ont montré que l'effet de la variation de température est plus prononcé sous une contrainte verticale supérieure à la pression de préconsolidation. Les indices de compression et de gonflement peuvent être considérés comme indépendants des variations de température. Donc le tassement global du remblai dû aux variations thermiques pourrait être considéré comme négligeable. Les résultats des essais de cisaillement direct ont montré que les variations de température (monotones ou cycliques) augmentent la cohésion ce qui est avantageux pour la capacité portante et la stabilité des pentes des remblais. Dans la phase de conception d'un remblai de stockage, ces résultats seraient utiles au dimensionnement du système si des trajectoires thermomécaniques similaires à celles de cette étude sont respectées. Dans une dernière partie, une simulation numérique prenant en compte l'interaction sol-atmosphère est réalisée afin d’évaluer la performance thermique de ce sol compacté en conditions naturelles. Différentes profondeurs d'installation de boucles d'échangeurs de chaleur sont testéss ainsi que différents scénarios de stockage. Les résultats ont montré que le sol compacté augmente de 8.5% les performances du système par rapport à l'installation d'une boucle horizontale dans le sol naturel (non compacté). Les résultats de deux scénarios différents ont montré qu’en été avec un fluide ayant une température d'entrée de 50 °C augmente significativement la performance du système. De plus, une installation plus profonde des boucles horizontales améliore également la performance du système. Il convient de noter que le remblai est en interaction avec l'atmosphère depuis ses surfaces supérieure et latérale, l'efficacité thermique de la structure pourrait être affectée en raison des pertes de chaleur. Par conséquent, il est préférable de placer les échangeurs de chaleur loin des surfaces supérieures et latérales.

Coarse-grained soils, which are materials containing grains ranging from micrometers to several tens of centimeters, are frequently used in various geotechnical projects such as dikes and embankments. The determination of their shear strength in standard laboratory devices is difficult because of the presence of large grains. Different approaches (scalping, substitution, and parallel gradation) could be used to reduce the grain size of the tested sample. However, these techniques involve a change in the percentage of each fraction in comparison to the initial sample. Therefore, it is important to know how the shear strength is altered by the variation in the grain size distribution curve. The aim of this study was to establish a methodology for estimating the shear strength of coarse-grained soils with matrix by testing their fraction compatible with the available shear device size. The parallel gradation method was used and the influence of the fines content increase in the reconstituted soil was investigated. Two soils with different fines content were studied: a limestone aggregate with 1.9% fines and a natural gravel with 15% fines. The shear strengths of parallel graded samples of these soils at the same dry density under saturated and unsaturated conditions were determined in devices with different sizes. The results showed, for the soil with fines content lower than 4%, a suitable estimation of the initial soil shear strength for a low grain breakage ratio. This low grain breakage ratio is ensured for low normal stresses, under 100 kPa in the case of the studied aggregate. For the soil with higher fines content, it has been shown that the initial soil friction angle is correctly estimated when the reconstituted soil has the same grain arrangement as the initial soil, i.e., for a fines content lower than 30%. However, the difference in fines content between the initial and reconstituted soils led to an overestimation of the initial soil cohesion. A cohesion – fines content relationship was proposed to predict the cohesion of the initial coarse-grained soil. Furthermore, when the fines content in the reconstituted soil is higher than 30%, it was shown that the scalping method provides a suitable estimation of the initial soil shear strength when the density and percentage of scalped grains criteria are fulfilled. Recommendations were made to determine the shear strength of coarse-grained soils with matrix based on their characteristics and the size of the available device.; Les sols grossiers à matrice, matériaux contenant des grains allant du micromètre à plusieurs dizaines de centimètres, sont fréquemment utilisés dans divers projets géotechniques tels que les digues et les remblais. La détermination de la résistance au cisaillement de ces sols dans les appareils standards de laboratoire est difficile en raison de la présence des grains de grande taille. Différentes approches (écrêtement, substitution et granulométrie parallèle) pourraient être utilisées pour réduire la taille des grains de l'échantillon à tester. Toutefois, ces techniques impliquent une modification du pourcentage de chaque fraction par rapport à l'échantillon initial. Il est donc important de connaître l'effet de la variation de la courbe granulométrique sur la résistance au cisaillement des sols grossiers à matrice. L'objectif de cette étude était d’établir une méthodologie permettant d’estimer la résistance au cisaillement des sols grossiers à matrice à partir d’essais sur leur fraction compatible avec les dispositifs de cisaillement disponibles. La méthode de granulométrie parallèle a été retenue et l’influence de l’augmentation du pourcentage de fines dans le sol reconstitué a été investiguée. Deux sols de différents pourcentages de fines ont été étudiés : un granulat calcaire ayant 1,9 % de fines et une grave naturelle ayant 15 % de fines. Les résistances au cisaillement d’échantillons de granulométrie parallèle de ces sols à la même densité sèche en conditions saturée et non saturée ont été déterminées dans des dispositifs de différentes dimensions. Les résultats ont montré une estimation satisfaisante de la résistance au cisaillement du sol grossier initial lorsque le pourcentage de fines est inférieur à 4 % avec un faible taux de rupture des particules. Ce faible taux est garanti pour de faibles contraintes normales, inférieures à 100 kPa. Pour un pourcentage de fines plus élevé dans le sol, soit moins 30 % de fines, il a été montré que l’angle de frottement du sol initial est bien estimé lorsque le sol reconstitué a le même arrangement des grains que le sol initial. Cependant, la différence de pourcentage de fines entre le sol initial et le sol reconstitué a conduit à une surestimation de la cohésion du sol initial. Une relation cohésion – pourcentage de fines a été établie pour prédire la cohésion du sol grossier initial. Par ailleurs, lorsque le pourcentage de fines dans le sol reconstitué est supérieur à 30 %, il a été montré que la méthode d’écrêtement permet d’obtenir une estimation satisfaisante de la résistance au cisaillement du sol initial lorsque les critères de densité et de pourcentage de grains écrêtés sont respectés. Des recommandations ont été faites pour déterminer la résistance au cisaillement des sols grossiers à matrice en fonction de leurs caractéristiques et la taille du dispositif disponible.

Coarse-grained soils, which are materials containing grains ranging from micrometers to several tens of centimeters, are frequently used in various geotechnical projects such as dikes and embankments. The determination of their shear strength in standard laboratory devices is difficult because of the presence of large grains. Different approaches (scalping, substitution, and parallel gradation) could be used to reduce the grain size of the tested sample. However, these techniques involve a change in the percentage of each fraction in comparison to the initial sample. Therefore, it is important to know how the shear strength is altered by the variation in the grain size distribution curve. The aim of this study was to establish a methodology for estimating the shear strength of coarse-grained soils with matrix by testing their fraction compatible with the available shear device size. The parallel gradation method was used and the influence of the fines content increase in the reconstituted soil was investigated. Two soils with different fines content were studied: a limestone aggregate with 1.9% fines and a natural gravel with 15% fines. The shear strengths of parallel graded samples of these soils at the same dry density under saturated and unsaturated conditions were determined in devices with different sizes. The results showed, for the soil with fines content lower than 4%, a suitable estimation of the initial soil shear strength for a low grain breakage ratio. This low grain breakage ratio is ensured for low normal stresses, under 100 kPa in the case of the studied aggregate. For the soil with higher fines content, it has been shown that the initial soil friction angle is correctly estimated when the reconstituted soil has the same grain arrangement as the initial soil, i.e., for a fines content lower than 30%. However, the difference in fines content between the initial and reconstituted soils led to an overestimation of the initial soil cohesion. A cohesion – fines content relationship was proposed to predict the cohesion of the initial coarse-grained soil. Furthermore, when the fines content in the reconstituted soil is higher than 30%, it was shown that the scalping method provides a suitable estimation of the initial soil shear strength when the density and percentage of scalped grains criteria are fulfilled. Recommendations were made to determine the shear strength of coarse-grained soils with matrix based on their characteristics and the size of the available device.; Les sols grossiers à matrice, matériaux contenant des grains allant du micromètre à plusieurs dizaines de centimètres, sont fréquemment utilisés dans divers projets géotechniques tels que les digues et les remblais. La détermination de la résistance au cisaillement de ces sols dans les appareils standards de laboratoire est difficile en raison de la présence des grains de grande taille. Différentes approches (écrêtement, substitution et granulométrie parallèle) pourraient être utilisées pour réduire la taille des grains de l'échantillon à tester. Toutefois, ces techniques impliquent une modification du pourcentage de chaque fraction par rapport à l'échantillon initial. Il est donc important de connaître l'effet de la variation de la courbe granulométrique sur la résistance au cisaillement des sols grossiers à matrice. L'objectif de cette étude était d’établir une méthodologie permettant d’estimer la résistance au cisaillement des sols grossiers à matrice à partir d’essais sur leur fraction compatible avec les dispositifs de cisaillement disponibles. La méthode de granulométrie parallèle a été retenue et l’influence de l’augmentation du pourcentage de fines dans le sol reconstitué a été investiguée. Deux sols de différents pourcentages de fines ont été étudiés : un granulat calcaire ayant 1,9 % de fines et une grave naturelle ayant 15 % de fines. Les résistances au cisaillement d’échantillons de granulométrie parallèle de ces sols à la même densité sèche en conditions saturée et non saturée ont été déterminées dans des dispositifs de différentes dimensions. Les résultats ont montré une estimation satisfaisante de la résistance au cisaillement du sol grossier initial lorsque le pourcentage de fines est inférieur à 4 % avec un faible taux de rupture des particules. Ce faible taux est garanti pour de faibles contraintes normales, inférieures à 100 kPa. Pour un pourcentage de fines plus élevé dans le sol, soit moins 30 % de fines, il a été montré que l’angle de frottement du sol initial est bien estimé lorsque le sol reconstitué a le même arrangement des grains que le sol initial. Cependant, la différence de pourcentage de fines entre le sol initial et le sol reconstitué a conduit à une surestimation de la cohésion du sol initial. Une relation cohésion – pourcentage de fines a été établie pour prédire la cohésion du sol grossier initial. Par ailleurs, lorsque le pourcentage de fines dans le sol reconstitué est supérieur à 30 %, il a été montré que la méthode d’écrêtement permet d’obtenir une estimation satisfaisante de la résistance au cisaillement du sol initial lorsque les critères de densité et de pourcentage de grains écrêtés sont respectés. Des recommandations ont été faites pour déterminer la résistance au cisaillement des sols grossiers à matrice en fonction de leurs caractéristiques et la taille du dispositif disponible.

Incorporation of heat exchangers in conventional geostructures like piles can extract the heat from the soil for heating purposes and inject it to the soil for cooling purposes. In recent years, research has been conducted at full and laboratory scale to investigate the effect of temperature on the geotechnical behavior of these energy geostructures as well as on the surrounding soil. Indeed, these energy geostructures can be subjected to cyclic mechanical loads and thermal variations throughout their lifetime. The aim of this study was to deepen the understanding regarding the behavior of sand/clay-structure contact under complex thermo-mechanical loads. A temperature-controlled direct shear device to perform monotonic and cyclic constant normal load or constant normal stiffness tests was developed. The response of the interface to the thermal effects on the mechanical behaviour of soils and soil-structure interface was investigated. Fontainebleau sand and kaolin clay were used as proxies for sandy and clayey soils. The results showed that the applied thermal variations have a negligible effect on the shear strength of the sand and sand-structure interface. In clay samples the temperature increase, increased the cohesion and consequently the shear strength, due to thermal contraction during heating. The adhesion of the clay-structure interface, was less than the cohesion of the clay samples. To investigate the mechanical cyclic load effects on the clay-structure interface at different temperatures, monotonic and cyclic constant-volume equivalent-undrained direct shear tests were performed on clay-clay and clay-structure interface at different temperatures. The results showed that, the number of cycles to failure for the clay-structure interface test was lower than that for the clay-clay case in the same range of cyclic and average shear stress ratios. Increasing the temperature, decreased the rate of strain accumulation and the number of cycles to failure increased by 2-3 times. The rate of degradation (degradation parameter, t) decreased by 16% with heating from 22 to 60oC for the different cyclic stress ratios tested. A non-isothermal soil-structure interface model based on critical state theory was then developed. The non-isothermal model takes into account the effect of temperature on the void ratio of interface prior to shearing. The model is capable to capture the effect of temperature on soil-structure interface under constant normal load and constant normal stiffness conditions for both sandy and clayey interfaces. The additional parameters have physical meanings and can be determined from classical laboratory tests. The formulation is in good agreement with the experimental results and the main trends are properly reproduced.; L'incorporation d'échangeurs de chaleur dans des géostructures conventionnelles comme les pieux peut extraire la chaleur du sol à des fins de chauffage et l'injecter dans le sol à des fins de refroidissement. Ces dernières années, des recherches ont été menées à l'échelle réelle et en laboratoire pour étudier l'effet de la température sur le comportement géotechnique de ces géostructures énergétiques ainsi que sur le sol environnant. En effet, ces géostructures énergétiques peuvent être soumises à des charges mécaniques cycliques et a des variations thermiques tout au long de leur durée de vie. L'objectif de cette étude était d'approfondir la compréhension du comportement du contact sable/argile-structure sous des charges thermomécaniques complexes. Un dispositif de cisaillement direct à température contrôlée permettant d'effectuer des essais monotones et cycliques à charge normale constante ou à rigidité normale constante a été mis au point. La réponse de l'interface aux effets thermiques sur le comportement mécanique des sols et l'interface sol-structure a été étudiée. Le sable de Fontainebleau et l'argile kaolin ont été utilisés comme substituts pour les sols sableux et argileux. Les résultats ont montré que les variations thermiques appliquées ont un effet négligeable sur la résistance au cisaillement de l'interface entre le sable et la structure du sol. Dans les échantillons d'argile, l'augmentation de la température a augmenté la cohésion et par conséquent la résistance au cisaillement, en raison de la contraction thermique pendant le chauffage. L'adhérence de l'interface argile-structure était inférieure à la cohésion des échantillons d'argile. Pour étudier les effets de la charge mécanique cyclique sur l'interface argile-structure à différentes températures, des essais de cisaillement direct monotone et cyclique à volume équivalent non drainé ont été réalisés sur l'interface argile-argile et argile-structure à différentes températures. Les résultats ont montré que le nombre de cycles jusqu'à la rupture pour l'essai d'interface argile-structure était inférieur à celui du cas argile-argile dans la même gamme de rapports de contraintes de cisaillement cycliques et moyennes. L'augmentation de la température a réduit le taux d'accumulation des contraintes et le nombre de cycles jusqu'à la rupture a été multiplié par 2 ou 3. Le taux de dégradation (paramètre de dégradation, t) a diminué de 16% avec un chauffage de 22 à 60 °C pour les différents rapports de contrainte cyclique testés. Un modèle d'interface sol-structure non isotherme basé sur la théorie de l'état critique a ensuite été développé. Le modèle non isotherme prend en compte l'effet de la température sur le taux de vide de l'interface avant le cisaillement. Le modèle est capable de saisir l'effet de la température sur l'interface sol-structure dans des conditions de charge normale constante et de rigidité normale constante pour les interfaces sableuses et argileuses. Les paramètres supplémentaires ont des significations physiques et peuvent être déterminés à partir d'essais classiques en laboratoire. La formulation est en bon accord avec les résultats expérimentaux et les principales tendances sont correctement reproduites.

Incorporation of heat exchangers in conventional geostructures like piles can extract the heat from the soil for heating purposes and inject it to the soil for cooling purposes. In recent years, research has been conducted at full and laboratory scale to investigate the effect of temperature on the geotechnical behavior of these energy geostructures as well as on the surrounding soil. Indeed, these energy geostructures can be subjected to cyclic mechanical loads and thermal variations throughout their lifetime. The aim of this study was to deepen the understanding regarding the behavior of sand/clay-structure contact under complex thermo-mechanical loads. A temperature-controlled direct shear device to perform monotonic and cyclic constant normal load or constant normal stiffness tests was developed. The response of the interface to the thermal effects on the mechanical behaviour of soils and soil-structure interface was investigated. Fontainebleau sand and kaolin clay were used as proxies for sandy and clayey soils. The results showed that the applied thermal variations have a negligible effect on the shear strength of the sand and sand-structure interface. In clay samples the temperature increase, increased the cohesion and consequently the shear strength, due to thermal contraction during heating. The adhesion of the clay-structure interface, was less than the cohesion of the clay samples. To investigate the mechanical cyclic load effects on the clay-structure interface at different temperatures, monotonic and cyclic constant-volume equivalent-undrained direct shear tests were performed on clay-clay and clay-structure interface at different temperatures. The results showed that, the number of cycles to failure for the clay-structure interface test was lower than that for the clay-clay case in the same range of cyclic and average shear stress ratios. Increasing the temperature, decreased the rate of strain accumulation and the number of cycles to failure increased by 2-3 times. The rate of degradation (degradation parameter, t) decreased by 16% with heating from 22 to 60oC for the different cyclic stress ratios tested. A non-isothermal soil-structure interface model based on critical state theory was then developed. The non-isothermal model takes into account the effect of temperature on the void ratio of interface prior to shearing. The model is capable to capture the effect of temperature on soil-structure interface under constant normal load and constant normal stiffness conditions for both sandy and clayey interfaces. The additional parameters have physical meanings and can be determined from classical laboratory tests. The formulation is in good agreement with the experimental results and the main trends are properly reproduced., L'incorporation d'échangeurs de chaleur dans des géostructures conventionnelles comme les pieux peut extraire la chaleur du sol à des fins de chauffage et l'injecter dans le sol à des fins de refroidissement. Ces dernières années, des recherches ont été menées à l'échelle réelle et en laboratoire pour étudier l'effet de la température sur le comportement géotechnique de ces géostructures énergétiques ainsi que sur le sol environnant. En effet, ces géostructures énergétiques peuvent être soumises à des charges mécaniques cycliques et a des variations thermiques tout au long de leur durée de vie. L'objectif de cette étude était d'approfondir la compréhension du comportement du contact sable/argile-structure sous des charges thermomécaniques complexes. Un dispositif de cisaillement direct à température contrôlée permettant d'effectuer des essais monotones et cycliques à charge normale constante ou à rigidité normale constante a été mis au point. La réponse de l'interface aux effets thermiques sur le comportement mécanique des sols et l'interface sol-structure a été étudiée. Le sable de Fontainebleau et l'argile kaolin ont été utilisés comme substituts pour les sols sableux et argileux. Les résultats ont montré que les variations thermiques appliquées ont un effet négligeable sur la résistance au cisaillement de l'interface entre le sable et la structure du sol. Dans les échantillons d'argile, l'augmentation de la température a augmenté la cohésion et par conséquent la résistance au cisaillement, en raison de la contraction thermique pendant le chauffage. L'adhérence de l'interface argile-structure était inférieure à la cohésion des échantillons d'argile. Pour étudier les effets de la charge mécanique cyclique sur l'interface argile-structure à différentes températures, des essais de cisaillement direct monotone et cyclique à volume équivalent non drainé ont été réalisés sur l'interface argile-argile et argile-structure à différentes températures. Les résultats ont montré que le nombre de cycles jusqu'à la rupture pour l'essai d'interface argile-structure était inférieur à celui du cas argile-argile dans la même gamme de rapports de contraintes de cisaillement cycliques et moyennes. L'augmentation de la température a réduit le taux d'accumulation des contraintes et le nombre de cycles jusqu'à la rupture a été multiplié par 2 ou 3. Le taux de dégradation (paramètre de dégradation, t) a diminué de 16% avec un chauffage de 22 à 60 °C pour les différents rapports de contrainte cyclique testés. Un modèle d'interface sol-structure non isotherme basé sur la théorie de l'état critique a ensuite été développé. Le modèle non isotherme prend en compte l'effet de la température sur le taux de vide de l'interface avant le cisaillement. Le modèle est capable de saisir l'effet de la température sur l'interface sol-structure dans des conditions de charge normale constante et de rigidité normale constante pour les interfaces sableuses et argileuses. Les paramètres supplémentaires ont des significations physiques et peuvent être déterminés à partir d'essais classiques en laboratoire. La formulation est en bon accord avec les résultats expérimentaux et les principales tendances sont correctement reproduites.

Compacted clays are used in many applications, including geotechnical and environmental geotechnical applications, due to their low permeability and retention properties. However, once in place, these materials could be exposed to thermal and/or water variations in the long and very long term. The main objective of this work is to experimentally quantify the impact of these variations on the compressibility of a compacted clay, and in particular its creep. With this objective, oedometric cells with controlled temperatures between 5 and 70°C were developed. Two types of oedometers with suction controlled by osmotic and saline methods were used in a suction range of 0 to 20.8 MPa, and at a constant temperature of 20°C. These devices were used to study creep up to a vertical stress of 3600 kPa. The study focused on the behavior of a moderately swelling compacted clay. The obtained results first showed that the yield stress σ’p decreases as the temperature increases. The creep coefficient Cαe increases with temperature, this effect being particularly marked at higher stresses. A linear relationship between the creep coefficient Cαe and the incremental compression index C*c was observed within the stress range considered and the ratio (Cαe /C*c) is temperature dependent. Then, two complementary experimental approaches (creep tests by steps or at controlled strain rate) highlighted the dependence of creep characteristics on soil suction. In addition, the yield stress σ’p increases with increasing strain rate έv and suction. In contrast, the compression index Cc and the creep coefficient Cαe vary in a non-monotonic manner with a maximum value under suction of 3.5 and 2 MPa, respectively. The evolution of these parameters appears to be strongly related to the internal structure of the soil. Analysis of the variation of σ’p with έv and Cαe with Cc showed that the relationship Δlog σ’p /Δlog έv =Cαe/Cc is also valid for the studied compacted clayey soil in saturated and unsaturated states. In conclusion, the results of this work allowed information to be gathered for better understanding the compressibility and creep behavior of compacted clayey soils as a function of temperature and suction; Les argiles compactées sont utilisées dans de nombreuses applications, notamment en géotechnique et en géotechnique de l’environnement, en raison de leur faible perméabilité, et de leurs propriétés de rétention notamment. Cependant, une fois en place, ces matériaux pourraient être exposés à des sollicitations thermiques et/ou hydriques, à long et très long terme. L’objectif principal de ce travail est de quantifier expérimentalement l’impact de ces sollicitations sur la compressibilité d’une argile compactée, et plus particulièrement son fluage. Avec cet objectif, des cellules œdométriques à température contrôlée entre 5 et 70°C ont été développées. Deux types d’œdomètre à succion contrôlée par les méthodes osmotique et solutions salines ont été employés dans une gamme de succion comprise entre 0 et 20,8 MPa, et à une température constante de 20°C. Ces dispositifs ont permis d’étudier le fluage jusqu’à une contrainte verticale de 3600 kPa. L’étude s’est concentrée sur le comportement d’une argile moyennement gonflante compactée. Les résultats obtenus ont tout d’abord montré que la contrainte de préconsolidation apparente σ’p diminue à mesure que la température augmente. Le coefficient de fluage Cαe augmente avec la température, cet effet étant plus particulièrement marqué à des contraintes plus élevées. Une relation linéaire entre le coefficient de fluage Cαe et l’indice de compression incrémental C*c a été observée dans la plage de contraintes considérée et le rapport (Cαe /C*c) dépend de la température. Ensuite, deux approches expérimentales complémentaires (essais de fluage par paliers ou à vitesse de déformation contrôlée) ont mis en évidence la dépendance des caractéristiques de fluage vis-à-vis de la succion du sol. Par ailleurs, la contrainte de préconsolidation apparente σ’p augmente avec l’augmentation de la vitesse de déformation έv et de la succion. En revanche, l’indice de compression Cc et le coefficient de fluage Cαe varient d’une manière non monotone avec une valeur maximale sous une succion de 3,5 et de 2 MPa, respectivement. L’évolution de ces paramètres apparaît fortement liée à la structure interne du sol. L’analyse de la variation de σ’p avec έv et de Cαe avec Cc a montré que la relation Δlog σ’p /Δlog έv = Cαe/Cc est également valable pour le sol argileux compacté étudié dans les cas saturés et non saturés

Compacted clays are used in many applications, including geotechnical and environmental geotechnical applications, due to their low permeability and retention properties. However, once in place, these materials could be exposed to thermal and/or water variations in the long and very long term. The main objective of this work is to experimentally quantify the impact of these variations on the compressibility of a compacted clay, and in particular its creep. With this objective, oedometric cells with controlled temperatures between 5 and 70°C were developed. Two types of oedometers with suction controlled by osmotic and saline methods were used in a suction range of 0 to 20.8 MPa, and at a constant temperature of 20°C. These devices were used to study creep up to a vertical stress of 3600 kPa. The study focused on the behavior of a moderately swelling compacted clay. The obtained results first showed that the yield stress σ’p decreases as the temperature increases. The creep coefficient Cαe increases with temperature, this effect being particularly marked at higher stresses. A linear relationship between the creep coefficient Cαe and the incremental compression index C*c was observed within the stress range considered and the ratio (Cαe /C*c) is temperature dependent. Then, two complementary experimental approaches (creep tests by steps or at controlled strain rate) highlighted the dependence of creep characteristics on soil suction. In addition, the yield stress σ’p increases with increasing strain rate έv and suction. In contrast, the compression index Cc and the creep coefficient Cαe vary in a non-monotonic manner with a maximum value under suction of 3.5 and 2 MPa, respectively. The evolution of these parameters appears to be strongly related to the internal structure of the soil. Analysis of the variation of σ’p with έv and Cαe with Cc showed that the relationship Δlog σ’p /Δlog έv =Cαe/Cc is also valid for the studied compacted clayey soil in saturated and unsaturated states. In conclusion, the results of this work allowed information to be gathered for better understanding the compressibility and creep behavior of compacted clayey soils as a function of temperature and suction, Les argiles compactées sont utilisées dans de nombreuses applications, notamment en géotechnique et en géotechnique de l’environnement, en raison de leur faible perméabilité, et de leurs propriétés de rétention notamment. Cependant, une fois en place, ces matériaux pourraient être exposés à des sollicitations thermiques et/ou hydriques, à long et très long terme. L’objectif principal de ce travail est de quantifier expérimentalement l’impact de ces sollicitations sur la compressibilité d’une argile compactée, et plus particulièrement son fluage. Avec cet objectif, des cellules œdométriques à température contrôlée entre 5 et 70°C ont été développées. Deux types d’œdomètre à succion contrôlée par les méthodes osmotique et solutions salines ont été employés dans une gamme de succion comprise entre 0 et 20,8 MPa, et à une température constante de 20°C. Ces dispositifs ont permis d’étudier le fluage jusqu’à une contrainte verticale de 3600 kPa. L’étude s’est concentrée sur le comportement d’une argile moyennement gonflante compactée. Les résultats obtenus ont tout d’abord montré que la contrainte de préconsolidation apparente σ’p diminue à mesure que la température augmente. Le coefficient de fluage Cαe augmente avec la température, cet effet étant plus particulièrement marqué à des contraintes plus élevées. Une relation linéaire entre le coefficient de fluage Cαe et l’indice de compression incrémental C*c a été observée dans la plage de contraintes considérée et le rapport (Cαe /C*c) dépend de la température. Ensuite, deux approches expérimentales complémentaires (essais de fluage par paliers ou à vitesse de déformation contrôlée) ont mis en évidence la dépendance des caractéristiques de fluage vis-à-vis de la succion du sol. Par ailleurs, la contrainte de préconsolidation apparente σ’p augmente avec l’augmentation de la vitesse de déformation έv et de la succion. En revanche, l’indice de compression Cc et le coefficient de fluage Cαe varient d’une manière non monotone avec une valeur maximale sous une succion de 3,5 et de 2 MPa, respectivement. L’évolution de ces paramètres apparaît fortement liée à la structure interne du sol. L’analyse de la variation de σ’p avec έv et de Cαe avec Cc a montré que la relation Δlog σ’p /Δlog έv = Cαe/Cc est également valable pour le sol argileux compacté étudié dans les cas saturés et non saturés