Post-liquefaction undrained monotonic behaviour of sands: experiments and DEM simulations

Abstract

This paper presents the results of a series of servo-controlled cyclic triaxial tests and numerical simulations using the three-dimensional discrete element method (DEM) on post-liquefaction undrained monotonic strength of granular materials. In a first test series, undrained monotonic tests were carried out after dissipating the excess pore water pressure developed during liquefaction. The influence of different parameters such as amplitude of axial strain, relative density and confining pressure prior to liquefaction on the post-liquefaction undrained response have been investigated. The results obtained highlight an insignificant influence of amplitude of axial strain, confining pressure and a significant influence of relative density on the post-liquefaction undrained monotonic stress–strain response. In the second series, undrained monotonic tests were carried out on similar triaxial samples without dissipating the excess pore water pressure developed during liquefaction. The results highlight that the amplitude of axial strain prior to liquefaction has a significant influence on the post-liquefaction undrained monotonic response. In addition, DEM simulations have been carried out on an assembly of spheres to simulate post-liquefaction behaviour. The simulations were very similar to the experiments with an objective to understand the behaviour of monotonic strength of liquefied samples from the grain scale. The numerical simulations using DEM have captured qualitatively all the features of the post-liquefaction undrained monotonic response in a manner similar to that of the experiments. In addition, a detailed study on the evolution of micromechanical parameters such as the average coordination number and induced anisotropic coefficients has been reported during the post-liquefaction undrained monotonic loading.