This paper focuses on an effective stress evaluation of the compression response of unsaturated soils during undrained compression to high stresses. During undrained compression of unsaturated soils containing a free gas phase, the void ratio, degree of saturation, pore air pressure, pore water pressure, and compressibility are expected to change in different ways. A modified form of Hilf's equation is combined with the isotropic stress-strain curve in terms of effective stress to predict the changes in pore water pressure. These results are compared with the results from undrained compression tests on unsaturated, compacted clay performed to mean total stresses of 160 MPa. The modified form of Hilf's equation and the effective stress analysis are found to provide a superior explanation of the compression response of unsaturated soils as compared to a conventional total stress analysis using Hilf's equation. The model is used to highlight new insights into the role of unsaturated conditions on the compression response of soils to high stresses, specifically focusing on an improved evaluation of soil response during buried explosions, impact loading, or compression of soils containing gases in energy geotechnics problems.

This study investigates the thermal soil-geosynthetic interaction mechanisms of reinforcing geotextiles confined in compacted silt that may be encountered when using mechanically-stabilized earth (MSE) walls as geothermal heat sinks. A thermo-mechanical geosynthetic pullout device was used that incorporates standard components for geosynthetic pullout or creep testing but also heating elements at the top and bottom of the soil box to apply boundary temperatures and dielectric sensors embedded in the soil layer to monitor distributions in temperature and volumetric water content. Two test series were performed: the first involves monotonic pullout of woven polypropylene geotextiles after reaching steady-state conditions under different boundary temperatures without a seating load, and the second involves monotonic pullout of woven polyethylene-terephthalate geotextiles after reaching steady-state conditions under different boundary temperatures with a seating pullout load. The results indicate that the pullout resistance of both geotextiles decreased with increasing temperature. Although heating led to drying of the unsaturated silt layers as expected, measurements from the second test series indicate accumulation of water at the silt-geotextile interface. An effective stress analysis considering thermal softening of soils indicates that the increase in effective saturation at the silt-geotextile interface was the cause of the decrease in pullout resistance with heating.