Multi-scale Analysis of Instability in Sand

Abstract

Instability of sand can occur under drained or undrained loading conditions in loose sand or dense sand. A micromechanics approach is used for the analysis of local instabilities of inter-particle contacts and their relations to the global instability of assembly. The comparisons between experimental and predicted results on Toyoura Sand show the capability of the model in capturing the modes of instability at the assembly level. Analysis at inter-particle contact level for loose sand under an undrained triaxial loading condition show that the number of unstable inter-particle planes increases continuously, while the assembly remains stable. The assembly becomes unstable when the sum of all local second-order work becomes zero. After this point, the overall shear stress begins to decrease during a strain controlled test, and progressively, more inter-particle contact planes become instable.