Discrete-Element Simulation of Dense Sand under Uni- and Bidirectional Cyclic Simple Shear Considering Initial Static Shear Effect

Abstract

Huge and critical structures, such as fuel storage tanks and nuclear power plants, are often built on dense sandy grounds, which may cause excessive plastic deformations under multidirectional cyclic shearing conditions caused by earthquakes. The lack of investigation of sand behavior under multidirectional loading may lead to unsafe designs, and thus significantly increase the maintenance cost for infrastructures during their long operational time, which might be longer than 100 years. This study presents a numerical investigation on the liquefaction behavior of dense sand under bidirectional cyclic simple shear using the discrete element method. The bidirectional cyclic simple shear tests with varying stress trajectories on the deviatoric stress plane, including figure-8, circular, and straight lines, were conducted. Additionally, a series of unidirectional loading tests was conducted in the simulation scheme for comparison purposes. The effect of the initial static shear on the cyclic behavior and liquefaction resistance of granular materials was examined. Four loading categories, including full reversal, partial reversal, intermediate reversal, and no reversal, were implemented in the numerical simulations. Although the presence of the initial static shear may enhance the cyclic resistance of granular samples under unidirectional loading, it mitigates the liquefaction resistance and promotes the failure of specimens under bidirectional shearing conditions. The microscopic analysis was performed to reveal the relationship between the fabric evolution and external loading, which can provide profound insights into the underlying mechanism of the cyclic behavior and liquefaction susceptibility of granular material when both the bidirectional shearing and initial static shear effects are considered.