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The compacted clay barrier of shallow depth repositories for wastes would be subjected to temperature variations. Consequently, the hydro-mechanical properties of compacted clays could be progressively modified, and thus affect the performance of repositories. The influence of effective stress and temperature on the creep behavior of a saturated compacted clayey soil was experimentally investigated by performing a series of incremental loading creep tests using a temperature-controlled oedometer. Applied effective vertical stress varied from 10 to 1300 kPa within a large temperature range of 5 ° C to 70 ° C. The results showed that the compression and swelling indices appear not to be affected by temperature, whereas the yield stress decreases as the temperature increases. The secondary compression is time-dependent; creep strains decrease with time till reaching a stable value corresponding to a period of 10 days. The creep coefficient C α e increases with the increase of the effective stress and temperature. Moreover, relationships between the creep coefficient C α e , incremental compression index C c ∗ , effective stress and temperature were further analyzed. A linear relationship between C α e and C c ∗ was observed in the considered stress range and the (C α e /C c ∗ ) ratio appears to be temperature dependent. Finally, the main results were discussed and interpreted in the light of a suitable constitutive framework.

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.

The main object of the study was to depict couplings between the hydromechanical behaviour of compacted clayey soil and the mineralogical and microstructural transformations induced by high-pH water. This high-pH water could be generated by the degradation of concrete lining of deep galleries in the context of the storage of nuclear wastes in deep facilities. The tested material is the clay that comes from the laboratory of the Meuse-Haute Marne laboratory (MHM-clay). Compacted MHM-clay samples were subjected to the circulation of high-pH water or natural sitewater over an 18-month period. The hydromechanical properties, microstructural characteristics and somephysicochemical properties of the sampleswere then determined (i.e., shear strength, swelling properties, retention curve, mineralogy and microstructure). After the circulation of high-pH water, a strong reduction of the swelling properties associated to an increase in friction angle was evidenced, whereas the hydrodynamic properties remained stable. These modifications were associated with an alteration of the fabric of the samples, i.e., the dissolution of the initial clay minerals and the precipitation of neoformed illite, which is a non-swelling mineral. The results demonstrated that chemohydromechanical couplings occurred during the circulation of high-pH water and resulted in the modification of the material's mineralogy. Thus, these processes are likely to alter the sealing characteristics of a backfill constructed from a compacted MHM-clay in the very long term.

International audience; Lightly loaded structures constructed on expansive soils may develop structural damage as a result of changes in the soil’s moisture content. This study investigated an analytical model of soil–structure interaction to assess the settlement of dwellings built on swelling soils when droughts occur. The building behavior was investigated with the Euler–Bernoulli beam theory, and the ground behavior was investigated with a Winkler-derived model based on the state surface approach. The analytical model results were compared to those of a finite element analysis using the Barcelona Expansive Model (BExM) performed with Code_Bright. The analytical model was then used to assess the settlement transmission ratio for a typology of clayey soils and different parameters of building. The results indicated that the final deflection of the building increased with the building length and soil suction. The building deflection due to the suction variations was inversely proportional to the load, the rigidity of the building and the embedding depth of the foundation. Increasing these parameters made the building less vulnerable to shrinkage and swelling action.

Despite the scant quantitative data available in the literature, it has been hypothesized that some chemical compounds can have deleterious effects on soil stabilization with lime and cements (e.g., nitrates, phosphates and chlorides). This study intends to assess their influence on soil stabilization quantitatively. An original experimental procedure was followed. Selected soils were mixed with a potential deleterious compound at a concentration representative of what can be found in the field. The performance of the different mixtures in terms of soil stabilization was then assessed by performing mechanical tests on samples submitted to several curing conditions (temperature and humidity). The results showed that the tested compounds are likely to alter the soil stabilization processes and thus lower the mechanical performance of the stabilized soil. The results also showed that it is not possible to determine a single threshold value for the compounds considered because their influence on soil stabilization is also a function of the nature of the soil (silt or fine sand), the type of cement (CEM I or CEM II) and the curing conditions.

This study presents the influence of suction variation on the fabric of two clayey soils, using the mercury intrusion porosimetry (MIP) technique on dense and loose remoulded samples. The experimental study focussed on the evolution of the compacted soil fabric, including the macropores, mesopores, and micropores under various hydromechanical conditions. The variation of void ratio of both samples was initially studied during a single wetting and drying cycle. The experimental results confirm the existence of a suction limit between the meso- and macropores (sm/M) as well as the soil “shrinkage limit” suction (sSL). The suction increase between (sm/M) and (sSL) completely eliminated the macropores and produced mesostructural rearrangement. The higher suctions modified the meso- and micropores. The measured soil water retention curves (SWRC) of these two soils compared with the MIP calculations showed a more reasonable agreement for the dense soil with a fewer macropores. Moreover, several wetting and drying cycles were applied to the remoulded samples. The suction cycles produced a cumulative swelling strain for the dense soil while a shrinkage accumulation was observed for the loose samples. The wetting/drying cycles induced an equilibrium stage in which the samples behaved in an elastic way. The analysis of the soil fabric at this elastic equilibrium stage showed that the suction cycles created significant macrostructural modifications and reorganization of the mesopores towards smaller sizes.

This study addresses firstly the soil fabric variations of loose and dense compacted soil samples during a single wetting/drying cycle at suctions between 0 and 287.9MPa using mainly the mercury intrusion porosimetry (MIP) tests. Two suction techniques were employed to apply this wide suction range: the osmotic technique for suctions less than 8.5MPa, and the vapor equilibrium or salt solution technique for suctions higher than 8.5MPa. Secondly, the soil water retention curves (SWRCs) were predicted by the MIP test results for both loose and dense soil samples. A reasonable correspondence between MIP results and SWRCs was found on the wetting path at lower suctions close to saturation and on drying path at higher suctions.

To further our knowledge of the coupling between the hydraulic cycles and mechanical behavior of treated swelling soils, this Note presents an experimental study on a bentonite/silt mixture treated with lime using a suction controlled osmotic oedometer. Successive wetting and drying cycles were applied at different suction ranges between 0 and 8 MPa, followed by a loading/unloading cycle at different suctions (2, 4 and 8 MPa). The compression curves of the aforementioned suctions provide the necessary information to analyze the influence of hydraulic cycles on the hydromechanical parameters of the treated swelling soils, such as the apparent preconsolidation stress P 0 ( s ) , the virgin compression index λ ( s ) and the unloading elastic index value κ. The suction ranges as well as the number of suction cycles influence the mechanical parameters of the treated swelling soil greatly.

This Note presents an experimental study performed on expansive compacted loose and dense samples using osmotic oedometers. Several successive wetting and drying cycles were applied in a suction range between 0 and 8 MPa under different values of constant net vertical stress (15, 30, and 60 kPa). During the suction cycles, the dense samples showed cumulative swelling strains, while the loose samples showed volumetric shrinkage accumulation. At the end of the suction cycles, the volumetric strains converged to an equilibrium stage that indicated elastic behavior of the swelling soil for any further hydraulic variations. At this stage, the compression curves for the studied soil at the different imposed suctions (0, 2, and 8 MPa) converged towards the saturated state curve for the high applied vertical stresses. We defined this pressure as the saturation stress ( P sat ) . The compression curves provided sufficient data to examine the soil mechanical behavior at the equilibrium stage. To cite this article: H. Nowamooz, F. Masrouri, C. R. Mecanique 337 (2009).

In the French model of deep nuclear wastes repositories, the galleries should be backfilled with excavated argillite after the site has been filled. After thousands of years, the degradation of the concrete lining of the galleries will generate an alkaline solute (pH > 12) that would circulate through the backfill. The goal of this paper is to describe the impact of such solute circulation on the properties of compacted argillite. Since additives (bentonite, sand or lime) are often introduced in the remoulded argillite for the backfill, such mixtures were also studied. Saturated-portlandite water was circulated through compacted samples for 3, 6 and 12 months at 60 °C. The shear strength behaviour of the samples was determined with triaxial tests. The microstructure of the samples was analysed via mercury intrusion porosimetry tests and scanning electron microscopy. The results showed that the influence of the alkaline fluid on the properties of the argillite is a function of the nature of the additive. In the case of the calcareous sand, no major changes were observed. The pure argillite underwent a slight decrease in its cohesion due to limited dissolution of its clayey particles. Conversely, intense alteration of the bentonite–argillite mixture was observed, and the shear strength behaviour was modified. Lime addition improved the mechanical characteristics of the argillite.

To further our knowledge of the coupling between the hydraulic and mechanical behaviours of the swelling soils, this paper presents an experimental study on a bentonite/silt mixture using an osmotic odometer. A loading/unloading cycle was applied to samples with different initial dry densities (1.27, 1.48, and 1.55 Mg m− 3) at different constant suctions (0, 2, and 8 MPa). We noted that the initial state of the soils after compaction significantly influenced the values of the apparent preconsolidation stress p0(s), the virgin compression index λ(s), and the elastic compression index κ. These experimental results provided a sufficient database to interpret the mechanical behaviour of the swelling soil and define three yielding surfaces: – the suction limit between micro- and macrostructure (sm/M) and the suction limit between nano- and microstructure (sn/m), which depend completely on the soil fabrics and the diameter separating the nano-, micro-, and macrostructure, – the Loading Collapse (LC) curve, representing the preconsolidation stress variation as a function of suction, – the Saturation Curve (SC), representing the variation of the saturation stress (Psat) as a function of suction. In general, we can state that the increase of compaction pressure unified the LC and SC surfaces and decreased the (sm/M) value without modifying the (sn/m) value.

To further our knowledge of coupling between the hydraulic cycles and mechanical behaviour of the swelling soils, this paper presents an experimental study on a bentonite/silt mixture using an odometer with suction controlled by the osmotic technique. A loading/unloading cycle was applied to each of the samples at different constant suctions (0, 2, 3 and 8 MPa). Moreover, successive wetting and drying cycles were applied under constant vertical stress at a suction range of 0 to 8 MPa, followed by a loading/unloading cycle at similar suctions (0, 2, 3 and 8 MPa). Finally, the compression curves of the aforementioned suctions with and without the application of suction cycles were compared, so as to analyse the influence of hydraulic cycles on the soil fabric and the mechanical parameters. It is observed that the wetting and drying cycles applied to both the micro- and macrostructure significantly influenced the virgin compression index λ(s), the apparent preconsolidation stress p0(s) and the elastic compression index values κ. However, the hydraulic cycles imposed only on the micro- or macrostructure induce negligible changes in the mechanical parameters of the soil.

Resume Cet article presente une etude menee sur un materiau gonflant compacte dans la gamme des succions comprises entre 8,5 et 287,9 MPa. Deux series d'essais œdometriques a succion controlee sont presentees. La premiere permet la caracterisation de l'evolution de la compressibilite avec la succion. Elle montre que la pression de preconsolidation apparente et la pente de compression plastique sont significativement influencees par la succion. La deuxieme serie etudie l'influence de sollicitations hydromecaniques complexes sur la compressibilite du materiau qui apparait tres dependante du chemin hydromecanique. Pour citer cet article : O. Cuisinier, F. Masrouri, C. R. Mecanique 331 (2003).

The deterministic Finite Element Method (FEM) is a valuable tool for understanding and predicting the mechanical behaviour of earth structures. The main difficulty in the application of this technique generally arises from the large uncertainties affecting the mechanical properties of materials to be introduced in the analysis. In many instances, these parameters should actually be considered as random variables or random fields. The Stochastic Finite Element Method (SFEM) should then be used to assess the results of the analyses in probabilistic terms. In this paper, the usefulness of the SFEM approach for engineering purposes is discussed and illustrated by analyses of embankments constructed by placing successive lifts of compacted soil. Construction materials are assumed to follow a simple non-linear constitutive law (Duncan JM, Chang CY. Non-linear analysis of stress and strain in soils, Journal of the Soils Mechanics and Foundation Division, ASCE 1970;96(5):1629–1653). Stochastic finite element analyses are performed using both the First Order-Second Moment method (FOSM) and Monte Carlo simulations (MC). A simple example shows that SFEM analyses can be useful to evaluate the relative influence of each of the parameters of the constitutive model on the results. Uncertainties affecting displacements, strains and stresses predictions for a large earth dam are also presented.

Resume Les schistes carton, materiaux surconsolides a l'etat intact, sont alterables et les variations de contraintes hydriques et/ou mecaniques peuvent modifier profondement leurs caracteristiques mecaniques. La progression du front de dessiccation et la conductivite hydraulique de ces materiaux, a l'etat non sature, sont etudiees experimentalement sur des eprouvettes provenant de la region de Pont-a-Mousson en Lorraine. L'evolution de la teneur en eau en fonction de la profondeur et les variations de la conductivite hydraulique permettent d'evaluer la profondeur potentiellement alterable de ces schistes carton.

This paper sets out to explore the changes in stress distribution for a medium reinforced by flexible geomembrane layers. The experimental results are compared to the theoretical results obtained using the Boussinesq method, and numerical results obtained using the Fast Lagrangian Analysis of Continua calculation program, (FLAC). The tests carried out on Schneebeli's analogical medium, which consists of a stack of small steel rollers, showed that, even in the case of loaded, non-reinforced soils, stress distribution follows Boussinesq's law; especially for high loads and despite the discrete nature of the experimental medium being used. In the case of loaded reinforced soil, the presence of reinforcing layers has no bearing on the vertical stress, while the horizontal stress, σx, shows a large increase.