Mechanical differences between sand and clay under monotonic and cyclic loading

摘要

The behavior of sand and clay under monotonic and cyclic loading is investigated numerically using the Super/subloading Yield Surface Cam-Clay model as typical responses in triaxial compression tests. This model is an elasto-plastic constitutive model, in which the concepts of soil structure, overconsolidation and anisotropy and their evolution laws are introduced to the modified Cam-Clay model. From the model responses it is found that the mechanical differences between sand and clay can be explained in terms of differences in the rates of structural decay, loss of overconsolidation, and increase/decrease of stress-induced anisotropy. The structure of sand is found to decay much more rapidly than clay, losing its overconsolidation and undergoing changes in anisotropy more gradually. These differences give rise to observed phenomena such as the rapid compaction of loose sand under cyclic loading in drained conditions and reduced effective stress under undrained conditions, leading to liquefaction; behavior that is not exhibited by structured clay.