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International audience; This paper explores the use of geotextiles as insulation material for energy geostructures made of compacted soil. This work is based on measurements of the thermal conductivity of four nonwoven needle-punched geotextiles of varying thicknesses made from virgin or recycled fibres. These values were measured using the hot-plate method. Then, to assess the use of these geotextiles under a covering soil layer, compression tests were performed. For each sample, the relation between thickness and vertical stress was thus established. The thermal conductivities varied from 0.04 to 0.06 W/m/K depending on the geotextile type and the compression stress applied. Subsequent measurements focused on the thermal conductivity of a bilayer compacted soil plus geotextile. Results revealed a water migration towards the geotextile and therefore a larger thermal conductivity. These results highlighted the main importance of compression load and moisture environment in the use of geotextiles as insulation products.

Reusing excavated material in geotechnical engineering reduces the carbon impact of a project. Such materials are usually placed in a compacted state in order to achieve the mechanical and hydric characteristics required to guarantee the safety of the structures. A good geotechnical knowledge of the materials is therefore necessary as well as a good anticipation of their behaviour over time. Indeed, in some situations, as in the case of waste storage, a low hydraulic conductivity is required. The use of crushed rocks rich in clays (argillite), possibly improved by adding bentonite, could be interesting. However, this addition, beneficial in terms of hydraulic conductivity, could be damaging from a mechanical point of view by the development of cracks at the interface atmosphere-compacted soil. For this purpose, samples compacted at the normal Proctor optimum are exposed to a relative humidity of 46% and a temperature of 22.5°C. The thickness, mass and surface condition (cracking) were monitored during the drying process, and measurements were taken in the thickness of the specimen after 29 hours of exposure. The results make it possible to compare the two materials at the same compaction energy. The argillite sample shows a significant shrinkage but no cracks at this scale. On the different hand, with the addition of bentonite, a significant cracking was observed and analysed. These results provide information on the hydromechanical behaviour of unsaturated fine soils at the atmosphere-compacted soil interface.

A well-known backfill soil was considered to be used as the backfill 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 materials. Two heat storage scenarios at three different installation depths were also investigated. The results 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 scenario. A deeper installation depth increases also the system performance.

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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; 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.

L’incorporation d’échangeurs de chaleur aux géostructures pose la question de l'impact des variations de température sur les paramètres géotechniques des sols. Dans cette étude, des essais mini-pressiométriques ont été réalisés sur des massifs de sol compactés dans un modèle réduit thermo-régulé. Un matériau limoneux compacté est soumis à trois cycles thermiques (20-50-20°C). Une diminution nette de la pression limite (Pl) et la pression de fluage (Pf) est mesurée tandis que l’évolution du module pressiométrique (EM) est beaucoup plus faible. Dans cet interval de température, l’effet de trois cycles de chauffage peut être considéré comme réversible., Academic Journal of Civil Engineering, Vol 35 No 1 (2017): Special Issue - RUGC 2017 Nantes

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.

Settlement and slope stability of an embankment are mechanical aspects that play a major role in structural safety. Due to the tendency towards renewable energy, the embankments can be considered as a suitable medium for thermal energy storage. Using horizontal heat exchanger tubes, the thermal energy will be stored in different compacted soil layers in an embankment. Therefore, this structure can be subjected to daily and seasonally temperature variations due to heat extraction. Cyclic temperature variation can modify the mechanical behavior of compacted soils. Thus this study aims to investigate the effect of monotonic and temperature cycles in the range of 5 to 50 oC, on consolidation parameters and shear characteristics of a compacted sandy lean clay. To achieve this, temperature-controlled oedometric and direct shear tests were performed. Results showed that the effect of heating and cooling on mechanical properties is more pronounced under vertical stresses higher than the preconsolidation pressure. By heating, the normal consolidation line shifted to the left and consequently, the apparent preconsolidation decreased. Compression and swelling indexes could be considered independent of temperature variation. Due to the temperature cycles, the volumetric response of the compacted soil in oedometric and shear tests was stress history-dependent. Results of the direct shear tests showed that by temperature variation (heating/cooling and temperature cycles) the cohesion increased and the friction angle remained unchanged.

International audience; Soil thermal properties are needed in specific engineering applications, such as the design of high-level radioactive waste disposal, buried power transmission cables and geothermal systems. The propagation of the heat flow in a soil exposed to a temperature gradient is based on three main soil thermal properties: the thermal conductivity (λ), the thermal capacity (C) and the thermal diffusivity (α = λ/C). The temperature variations affect the physical properties of soil, inducing changes in its thermal properties. In this study, the evolution of thermal properties of different compacted soils exposed to cyclic temperature variations were investigated through laboratory tests. The results showed that at 20 °C, the thermal conductivity of the compacted soils increased on the dry side of the compaction curve until it reached a maximum near the optimum water content. Variation of λ in a temperature range of 1–20 °C was not shown, but a slight increase of λ was measured in the range of 20–40 °C, which was clearly confirmed in the range of 40–70 °C. The application of cyclic temperature variations to the samples showed partially reversible evolution of thermal conductivity and totally reversible evolution of volumetric heat capacity.

The incorporation of heat exchangers in geostructures changes the temperature of the adjacent soil, raising important issues concerning the effect of temperature variations on hydro-mechanical soil behaviour. The objective of this paper is to improve the understanding and quantification of the impact of temperature variation on the bearing capacity of thermo-active piles. Currently, the design of deep foundations is based on the results of in situ penetrometer or pressuremeter tests. However, there are no published data on the effect of temperature on in situ soil parameters, preventing the specific assessment of the behaviour of thermo-active piles. In this study, an experimental device is developed to perform mini-pressuremeter tests under controlled laboratory conditions. Mini-pressuremeter tests are performed on an illitic soil in a thermo-regulated metre-scale container subjected to temperatures from 1 to 40 °C. The results reveal a slight decrease in the pressuremeter modulus (E p) and a significant decrease in the creep pressure (p f) and limit pressure (p l) with increasing temperature. The results also reveal the reversibility of this effect during a heating–cooling cycle throughout the investigated temperature range, whereas the effect of a cooling–heating cycle was only partially reversible. In the case of several thermal cycles, the effect of the first cycle on the soil parameters is decisive.

International audience; Thermal energy storage in compacted soils can be considered as a new economically efficient and environmentally friendly technology in geotechnical engineering. Compacted soils are usually unsaturated; therefore, reliable estimates and measurements of their thermal properties are important in the efficiency analysis of these structures. In this study, a method is used to estimate the thermal properties of an unsaturated compacted soil. Several temperature sensors were placed in a thermo-regulated metric scale container to monitor the imposed temperature variation in the range of the 20 to 50 °C. This imposed temperature variation reproduced the temperature variation in the thermal energy storages. An inverse analytical model based on a one-dimensional radial heat conduction equation is used to estimate the thermal diffusivity using the temperature variation between two temperature sensors. The volumetric heat capacity was measured using a calorimeter in the laboratory, enabling the estimation of the thermal conductivity of the compacted soil. Then, this estimated thermal conductivity was compared with the thermal conductivity values measured with two other methods (steady-state and transient-state method). The difference between them are discussed in terms of the sample heterogeneity, sample size, and measurement method.

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International audience; In geotechnical engineering, the proper design of thermo-active geostructures (piles, foundations, etc.) and deep waste storage disposals requires a better understanding of the thermo-hydro-mechanical behaviour of natural and compacted soils. Important mechanical parameters of the soils such as the cone resistance (qc) and the friction sleeve resistance (fs) are usually obtained by penetration in-situ tests. In the present study, penetration tests adapted from the static penetration method were conducted in laboratory, using a mini-penetrometer, to characterise compacted samples. The objective was to examine and quantify the influence of temperature changes on penetration parameters of two different compacted soils. Samples of an illitic material and the kaolinite–sand mixture compacted at different initial water contents and dry densities were subjected to a range of temperatures from 1 to 70 °C. The cone resistance (qc) and the friction sleeve resistance (fs) were measured. Obtained results showed that the particle size, the density and the nature of compacted soils have an important effect on the penetration test parameters. For illitic samples, we obtained significant variation of the cone resistance and friction sleeve resistance with temperature on the dry side of the compaction curve while limited changes were observed on the wet side. For the kaolinite–sand mixture, the temperature effect on these two parameters was negligible.

International audience; Soil cracking has been studied for many decades; however, it still deserves further investigation. This paper describes a new testing device that uses image processing to perform simultaneous and continuous quantification of the vertical strain and radial strain, crack area, and water content of a soil specimen subjected to suction cycles imposed by the vapour equilibrium method. An image processing method was designed to determine the crack area and the soil radial strain separately. The evolution of each measured parameter over time in a clayey soil specimen subjected to 3 suction cycles is presented and discussed. The first suction cycle has the greatest impact on the crack area, the mass water content, the vertical strains and the radial strains. Hysteresis loops were observed for crack area and radial strain evolution.

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

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.

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International audience; The incorporation of heat exchangers in geostructures produces a cyclic variation of the temperature in the adjacent soil. Therefore, there are important questions about the effect of temperature variations on hydro-mechanical soil parameters. In this study, the mini-pressuremeter tests were conducted in laboratory on a homogeneous material submitted to different thermal loading (1 to 40 °C). The tested material, an illitic soil, is compacted in a thermo-regulated container at optimal water content (31.3 %) and 90% of maximal dry density (1.29 Mg/m 3). Only six tests are performed in each container to prevent edge effects and the influence between the tests. The impact of temperature variation on creep pressure (pf), limit pressure (pl) and pressuremeter modulus (Ep) were determined. A decrease in creep pressure and limit pressure with increasing temperature was observed, while the variation of pressuremeter modulus was less pronounced. The first cycle induced more important parameter variations than the subsequent cycles.

In geotechnical engineering, the proper design of thermo-active geostructures requires a better understanding of the thermo-hydro-mechanical behaviour of natural and compacted soils. For design purposes, mechanical parameters are usually obtained by pressuremeter in-situ tests. In the present study, mini-pressuremeter tests were conducted in laboratory to characterise compacted soils. The objective was to examine and quantify the influence of temperature cyclic changes on pressuremeter parameters of two different compacted soils. A heating-cooling cycle (20-40-20 °C) was applied to a clayey compacted soil, and three heating-cooling cycles (20-50 °C) were applied to a compacted loam. The obtained results showed a decrease in limit pressure (Pl) and creep pressure (Pf) with increasing temperature for both tested soils, while the variation of the pressuremeter modulus (EM) was less significant. Through the temperature range tested, a reversibility of the effect of a heating cycle is obtained. These results were quite similar for both studied materials and the application of several thermal cycles did not modify the reversibility of the evolution., L’incorporation d’échangeurs de chaleur aux géostructures pose la question de l'impact des variations de température sur les paramètres géotechniques des sols. Le dimensionnement des capacités portantes des fondations profondes peut être basé sur les résultats d’essais pressiométriques ou pénétrométriques. Dans cette étude, des essais mini-pressiométriques ont été réalisés sur des massifs de sol compactés dans un modèle réduit thermo régulé. Un matériau argileux est soumis à un cycle de réchauffement (20-40-20°C) tandis qu’un matériau limoneux est soumis à trois cycles thermiques (20-50-20°C). Une diminution nette de la pression limite (Pl) et la pression de fluage (Pf) sur chaque sol est mesurée tandis que l’évolution du module pressiométrique (EM) est beaucoup plus faible. Dans ces intervalles de température, l’effet des cycles de chauffage est réversible. La normalisation des résultats montre une similarité des évolutions pour les deux matériaux.

International audience

International audience

International audience

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.

Energy geostructures involve providing a direct heat exchange with the ground through integrated systems in the foundations or geotechnical structures. The incorporation of heat exchangers in geostructures produces a cyclic variation of the temperature in the adjacent soil. Therefore, there are important scientific questions about the effect of temperature variations on hydro-mechanical soil parameters in general, and particularly for sensitive clay soils. The main objective of this thesis is to improve the understanding and the quantification of the impact of temperature variation on the bearing capacity of geothermal piles. Currently, the design of the bearing capacity of deep foundations is based on the results of in situ penetrometer and pressuremeter tests. Herein, experimental methods are developed to carry out these tests in laboratory conditions. Mini-penetrometer tests were carried out on samples compacted at different initial states and subjected to temperature variations ranging from 1 to 70 °C. The results showed a significant change in the studied parameters: the cone resistance (qc) and the friction sleeve resistance (fs) for an illitic material compacted on the dry side of the compaction curve. Mini-pressuremeter tests performed on the same illitic compacted soil in a thermo-regulated metric scale container, showed a decrease in creep pressure (pf) and limit pressure (pl) with increasing temperature, while the variation of pressuremeter modulus (EM) is less pronounced. The results showed a quasi-reversibility of the effect of a heating cycle through the temperature range tested, while the effect of a cooling cycle was only partially reversible. In the case of several thermal cycles, the first cycle induced more important parameter variations than the subsequent cycles, and at the end of the experimentation. Further analysis of the evolution of the thermal properties (thermal conductivity ([lambda]), heat capacity (Cv) and thermal diffusivity (D)) within heating and cooling process as a function of soil water content and dry density showed an increase of these parameters with the increase of initial values of w and [rho]d, and an increase of [lambda] in the dry side of the compaction curve with increasing temperature from 1 to 70 °C. In summary, for the energy piles driven in the clay soils, some modifications in the bearing capacity have to be taken into account due to the variation of the hydro-mechanical parameters of the soil induced by thermal cycles, Les géostructures énergétiques consistent à établir un échange thermique direct avec le sol grâce à des systèmes intégrés dans les fondations ou les structures géotechniques. L’incorporation des échangeurs de chaleur aux géostructures provoque une variation cyclique de la température du sol adjacent. Des questions se posent sur l'impact de ces variations thermiques sur les paramètres géotechniques des sols en général, et en particulier des sols sensibles argileux. L’objectif de cette thèse est d’améliorer la compréhension et la quantification de l’impact de la variation de la température sur la capacité portante des pieux géothermiques. Actuellement, le dimensionnement des capacités portantes des fondations profondes est basé sur les résultats d’essais pénétrométriques ou pressiométriques. Des méthodes expérimentales ont été développées afin de permettre la réalisation de ces essais dans les conditions du laboratoire. Des essais mini-pénétrométriques sont réalisés sur des éprouvettes compactées à différents états initiaux et soumises à des températures variant de 1 à 70 °C. Les résultats montrent une évolution sensible des paramètres étudiés, la résistance en pointe (qc) et le frottement latéral (fs), pour un matériau illitique, lorsqu’il est compacté du côté sec de l’optimum. Les essais mini-pressiométriques, réalisés sur des massifs de sol illitique compactés en modèle réduit d’échelle métrique dans une cuve thermo-régulée, ont montré une diminution de la pression de fluage (pf) et de la pression limite (pl) avec l’augmentation de la température, tandis que la variation du module pressiométrique (EM) est moins marquée. Les résultats montrent une quasi-réversibilité des effets d’un cycle de chauffage dans la gamme de température testée alors que l’effet d’un cycle de refroidissement n’est que partiellement réversible. Pour les essais soumis à plusieurs cycles thermiques, le premier cycle induit des variations de paramètres toujours plus importantes que les cycles suivants. Une analyse approfondie de l’évolution des propriétés thermiques (la conductivité thermique ([lambda]), la capacité thermique volumique (Cv) et la diffusivité thermique (D)) des sols en fonction de la teneur en eau, de la masse volumique sèche et de la température montre une augmentation de ces paramètres avec l’augmentation de w et [rho]d et une augmentation de [lambda] des éprouvettes illitiques du côté sec de l’optimum avec l’augmentation de la température de 1 à 70 °C. En résumé, pour les pieux énergétiques, les résultats obtenus en laboratoire montrent une modification de la capacité portante due à la variation des paramètres du sol illitique sous l’effet des cycles thermiques