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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.

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.

SOLSA is the first automated expert system for on-site cores analysis. The scope is to provide a prototype to be an innovative and necessary tool for geo-metallurgy, in order to optimize the valorization of the ore. The Expert System consists in the combination of an integrated drilling rig providing cores of high quality, an automated scanner and phase identification software, developed for nickel laterites and bauxites but usable as well in other sectors. SOLSA combines non-destructive sensors and the whole system is driven by an innovative, user-friendly and intelligent software. SOLSA provides more complete information while optimizing the exploration stage, with a significant reduction of costs and return time. Such objective involves, in the first place, to fast, cheaper and systematic acquisition of the data needed for optimizing the process. The adding value takes place first at the exploration or grade control stage, furnishing systematic characterization and regionalization of the different types of ore. Then such information can be used for improving the ore scheduling at the mining and processing stages, toward improving the recovery and efficiency of the processing

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; 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. Fontainebleau sand and kaolin clay were used as proxies for sandy and clayey soils. The sandy soil was prepared in a dense state,and the clayey soil was prepared in a normally consolidated state. The results showed that the applied thermal variations have a negligible effect on the shear strength of the sand and sand-structure interface under CNL and CNS conditions, and the soil and soil- structure interface behaviour could be considered thermally independent. 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; 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.

In energy geostructures, which exploit the heat in soil using earth contact elements, the interface is subjected to cyclic thermo-mechanical loads. Monotonic and cyclic constant-volume equivalent-undrained (CVEU) direct shear tests were performed on clay-clay and clay-structure interface at different temperatures (22 and 60 °C). Different cyclic and average stress ratios (CSR and ASR) were applied to the kaolin clay-structure interface under 300 kPa of normal stress. 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. In cyclic clay-structure tests, decreasing the cyclic stress ratio, increased the number of cycles to failure; however, decreasing the average shear stress ratio decreased the number of cycles to failure. 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 60 °C for the different cyclic stress ratios tested.

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; 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, 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 with 0.6 m diameter and 0.8 m height, at optimal water content (31.3 %) and 90% of maximum 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.

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

National audience; 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.; Les géostructures énergétiques consistent à établir un échange thermique avec le sol directement grâce à des systèmes intégrés dans les fondations ou la structure. L’incorporation des échangeurs de chaleur aux géostructures pose des questions sur l'impact des variations de température sur les paramètres géotechniques des sols sensibles (illite, smectite...). Le dimensionnement des capacités portantes des fondations prof ondes est basé sur l es résultats d’essais pressiométriques ou pénétrométriques. Dans cette étude, des essais mini-pressiométriques ont été réalisés dans des conditions de laboratoire sur un massif de sol compacté dans un modèle réduit thermorégulé. Le matériau argileux testé, riche en illite, est préparé à une masse volumique sèche de 1,29 Mg/m 3 et une teneur en eau de 31,3 % puis soumis à des températures de 1, 20 et 40 ° C. L’impact de la variation de la température a été mis en évidence sur la pression limite (p l ) et la pression de fluage (p f ).

National audience; 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.; Les géostructures énergétiques consistent à établir un échange thermique avec le sol directement grâce à des systèmes intégrés dans les fondations ou la structure. L’incorporation des échangeurs de chaleur aux géostructures pose des questions sur l'impact des variations de température sur les paramètres géotechniques des sols sensibles (illite, smectite...). Le dimensionnement des capacités portantes des fondations prof ondes est basé sur l es résultats d’essais pressiométriques ou pénétrométriques. Dans cette étude, des essais mini-pressiométriques ont été réalisés dans des conditions de laboratoire sur un massif de sol compacté dans un modèle réduit thermorégulé. Le matériau argileux testé, riche en illite, est préparé à une masse volumique sèche de 1,29 Mg/m 3 et une teneur en eau de 31,3 % puis soumis à des températures de 1, 20 et 40 ° C. L’impact de la variation de la température a été mis en évidence sur la pression limite (p l ) et la pression de fluage (p f ).

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.