Constitutive Model for the Undrained Compression of Unsaturated Clay

This paper proposes a constitutive model to describe the isotropic compression response of unsaturated, compacted clay under undrained conditions over a wide range of mean stresses. The total stress-based model captures the impacts of the initial degree of saturation on the apparent preconsolidation stress and the slope of the compression curve up to the point of pressurized saturation. The points of pressurized saturation for specimens with different initial degrees of saturation were predicted using a modified form of a pore-pressure analysis from the literature. The compression response for pressure-saturated specimens was dominated by the pore water, although dissolved air and soil structure may play a role for some soils. The model was calibrated using results from a series of compression tests on compacted clay specimens having initial degrees of saturation ranging from 0.6 to 1.0 and the same initial void ratio. The model was found to provide a good match to the experimental data for mean stresses up to 160 MPa, in particular due to the improvements in the analysis from the literature to evaluate the points of pressurized saturation. (C) 2016 American Society of Civil Engineers.