Effects of deviator strain histories on liquefaction of loose sand using DEM

A series of undrained tests on loose sand with different pre-shearing histories are conducted in three-dimensional discrete element method (DEM) simulations. The pre-shearing histories are simulated under drained conditions with different pre-shearing strain levels ranging from 0% to 1.57%. Two different pre-shearing history types (pre-shearing cycle and pure pre-shearing) are investigated and compared. The quasi-steady state, or temporary liquefaction, is found in all undrained tests. Both macroscopic and microscopic behaviours show that pre-shearing histories can stabilize the undrained behaviour and even re-establish a solid-like behaviour. The triggering of temporary liquefaction is well captured by the redundancy index and the macroscopic behaviours can be well correlated with the evolution of the redundancy index. There exists a limiting undrained stress path on the stress plane that all the samples with pre-shearing cycles cannot go beyond, indicating that the samples have a ‘memory’. The shear-induced anisotropy in the samples with a pure pre-shearing history leads to higher initial peak values of deviator stress than those for the corresponding samples with pre-shearing cycles under undrained simulations. The ultimate stress ratio of deviator stress against effective mean stress after temporary liquefaction is found to be unique and independent of the types and levels of pre-shearing histories.