Undrained cyclic behavior of granular materials considering initial static shear effect: Insights from discrete element modeling

Abstract

In-situ soil deposits often have an initial shear stress that significantly affects their subsequent cyclic behavior and liquefaction susceptibility. This is closely related to the internal structure of the soil but is very difficult to study thoroughly through conventional laboratory tests. In this study, a numerical procedure that can impose arbitrary two-dimensional stress or strain paths was developed using the discrete element method (DEM); this procedure was then used in simulations to investigate the behavior of granular polygonal samples under an undrained cyclic simple shear with various densities and stress conditions. Two types of cyclic responses could be identified from the simulation results: “cyclic liquefaction” and “residual deformation failure.” It was found that the initial static shear could either enhance or weaken the cyclic resistance of sand to liquefaction failure, depending on the extent of the shear stress reversal. The internal structure of the granular materials was quantified using a contact-normal-based fabric tensor that could describe their load-bearing characteristics in response to the external applied stress. The norm and principal direction of the fabric tensor both exhibited drastically different evolution patterns under varying loading conditions. This can provide further insights into the underlying failure mechanism of granular soils.