Fabric evolution of granular soils under multidirectional cyclic loading

Cyclic behavior of granular soils under multidirectional shaking is significantly different from that under unidirectional loading. In this study, a series of undrained simple shear simulations were conducted using a discrete-element method (DEM) under unidirectional and multidirectional loading conditions. Although the excess pore water pressure within a sample cannot reach the initial confining pressure, large shear strains of a similar amplitude still develop in samples under multidirectional loading. The simulation results further illustrate that granular soils have vastly different liquefaction resistance under different loading conditions. Evolution of soil fabric is also quantitatively studied in terms of inter-particle contacts and particle-void distribution. The same “stable state” of soil fabric will be reached under different multidirectional loading paths, which corresponds to that of a post-failure hardening state under unidirectional loading. The DEM study provides a new perspective in terms of microstructure evolution of granular soils under a variety of loading conditions.