Effects of initial static shear on liquefaction behaviour of Toyoura sand in undrained multi direction dynamic cyclic simple shear tests and DEM

Abstract

Initial static shear history has been shown to be a critical factor in the liquefaction behaviour of sand. This paper presents a comprehensive study of liquefaction behaviour of Toyoura sand under initial static shear by conducting multi direction dynamic cyclic simple shear(MDDCSS) tests and numerical simulations based on the discrete element method(DEM). These two methods are complementary to each other. The test results showed that the observed types of failure could be distinguished into flow liquefaction, cyclic mobility and residual deformation accumulation, and the types of failure are related to the initial relative density, initial static shear and cyclic shear stress amplitude. The typical failure mode of loose sand is flow liquefaction, while the medium-dense and dense sand are cyclic mobility and residual deformation accumulation. The effect of initial static shear will reduce the dynamic strength of Toyoura sand and have different effect on sand with different initial relative density. The dynamic strength of loose and medium-dense sand decreases with the increase of initial static shear. The dynamic strength of dense sand decreases first and then increases with the increase of initial static shear. In addition, for loose and medium-dense sand, the liquefaction resistance when the initial static shear is perpendicular to cyclic shear stress is greater than that in parallel. For dense sand, when the initial static shear ratio is less than 0.2, the liquefaction resistance when the initial static shear is perpendicular to cyclic shear stress is greater than that in parallel. Otherwise, the liquefaction resistance under the initial static shear perpendicular to the cyclic shear stress is less than that under parallel.