CAVITY EXPANSION IN UNSATURATED SANDS

Abstract. A constitutive model for the stress-strain behaviour of sands while unsaturated and subjected to high stresses is presented and implemented into a cavity expansion analysis. The concepts of critical state soil mechanics and bounding surface plasticity theory are adopted. The model is formulated in an effective stress framework and suction is introduced as a hardening parameter. Attention is given to particle crushing associated with the high stresses surrounding the cavity through the shape of the critical state line. The versatility of the model lies in its ability to simulate using suction independent material parameters the stress-strain behaviour of an unsaturated quartz sand subjected to various load paths across a range of stress magnitudes. The cavity expansion problem is solved using the similarity technique, extended for application to unsaturated soils. Constant suction and constant moisture content drainage conditions are considered. Substantial differences in the cavity pressure−cavity strain relationships are observed for the saturated and unsaturated conditions. In particular, it is shown that the limit pressure of the expanding cavity is significantly greater for the unsaturated condition. This is of major significance when using cavity expansion theory to interpret the cone penetration and pressuremeter tests