Swelling Soils Behaviour in Cyclic Suction-Controlled Drying and Wetting

Cyclic drying and wetting phenomena of the expansive clayey soils cause the progressive settlements which could affect principally the foundations of buildings, the drainage channels and the buffers in radioactive waste disposals. In order to better understand the coupling between these hydraulic cycles and the mechanical behaviour of the swelling soils, this article presents an experimental study performed on two different expansive soils (molded and natural) using oedometer tests by imposing suction variations with the osmotic technique. Several successive swelling and shrinking cycles were applied under different constant vertical net stresses. During the suction cycles, the compacted samples showed cumulative shrinkage strains. On the other hand, the natural samples presented cumulative swelling strains. At the end of the suction cycles, the volumetric strains reached an equilibrium stage which indicates an elastic behaviour of the samples. We can relate these elastic behaviours to the soil fabric and especially to the microstructural content of soil

Seasonal thermal energy storage in shallow geothermal systems: thermal equilibrium stage

This paper is dedicated to the study of seasonal heat storage in shallow geothermal installations in unsaturated soils for which hydrothermal properties such as degree of saturation and thermal conductivity vary with time throughout the profile. In the model, a semi-analytical model which estimates time-spatial thermal conductivity is coupled with a 2D cylindrical heat transfer modeling using finite difference method. The variation of temperature was obtained after 3 heating and cooling cycles for the different types of loads with maximum thermal load of qmax = 15 W.m−1 with variable angular frequency (8 months of heating and 4 months of cooling).and constant angular frequency (6 months of heating and 6 months of cooling) to estimate the necessary number of cycles to reach the thermal equilibrium stage. The results show that we approach a thermal equilibrium stage where the same variation of temperature can be observed in soils after several heating and cooling cycles. Based on these simulations, the necessary number of cycles can be related to the total applied energy on the system and the minimum number of cycles is for a system with the total applied energy of 1.9qmax

Shakedown modeling of unsaturated expansive soils subjected to wetting and drying cycles

It is important to model the behavior of unsaturated expansive soils subjected to wetting and drying cycles because they alter significantly their hydro-mechanical behavior and therefore cause a huge differential settlement on shallow foundations of the structure. A simplified model based on the shakedown theory (Zarka method) has been developed in this study for unsaturated expansive soils subjected to wetting and drying cycles. This method determines directly the stabilized limit state and consequently saves the calculation time. The parameters of the proposed shakedown-based model are calibrated by the suction-controlled oedometer tests obtained for an expansive soil compacted at loose and dense initial states, and then validated for the same soil compacted at intermediate initial state by comparing the model predictions with the experimental results. Finally, the finite element equations for the proposed shakedown model are developed and these equations are implemented in the finite element code CAST3M to carry out the full-scale calculations. A 2D geometry made up of the expansive soil compacted at the intermediate state is subjected to successive extremely dry and wet seasons for the different applied vertical loads. The results show the swelling plastic deformations for the lower vertical stresses and the shrinkage deformations for the higher vertical stresses

Comportement hydromécanique des sols gonflants soumis :les hydriques

Cet article rapporte les résultats d’études expérimentales effectuées à l’œdomètre avec imposition de succion par la méthode osmotique sur des matériaux gonflants compactés et naturels. Plusieurs cycles de séchage/humidification ont été appliqués sur deux matériaux sous trois faibles charges mécaniques constantes. Pendant ces cycles, les éprouvettes manifestent un retrait ou un gonflement cumulé. Les résultats montrent que dans les deux cas, les déformations volumiques convergent vers un état d’équilibre où le sol présente un comportement réversible. L’ensemble de ces résultats a été analysé dans le cadre du modèle élastoplastique (BExM) propose par Alonso et al. (1999) qui prend en compte l’accumulation des déformations lors de l’application de différents chemins de chargement

A numerical study into effects of soil compaction and heat storage on thermal performance of a Horizontal Ground Heat Exchanger

International audienceThe 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