UC San Diego

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.