Numerical study of soil collapse behavior by discrete element modelling

In unsaturated granular soil, capillary suction produces an adhesive force that acts perpendicular to the tangential plane at each contact point. In this paper, the collapse behavior of unsaturated granular soil during isotropic compression and biaxial shear are numerically simulated using the distinct element method (DEM) by incorporating this adhesive force initially at all contacts and then releasing it continuously to zero. The simulated results are compared with the results of triaxial compression tests on unsaturated compacted clay and qualitative similarities are obtained. Based on the simulation results, the yield stresses under different interparticle adhesive forces are determined and the collapse processes before and after yielding are investigated in detail. Moreover, the effect of initial void ratio and principal stress ratio on collapse is also investigated and discussed. The paper illustrates the capacity of simulating qualitatively the collapse behavior of unsaturated granular soils through the changes of the interparticle adhesive forces produced by the capillary suction. (C) 2003 Elsevier Science Ltd. All rights reserved.