DEM Study on the Instability Behaviour of Granular Materials

This paper presents the discrete element method (DEM) simulations on the instability behaviour of granular materials during constant shear drained condition (CSD). CSD condition was implemented by decreasing mean effective stress on an assembly of particles under strain controlled loading. In this study, the instability condition was predicted at the particle scale level using particle second order work increment (Nicot et al. in Int J Solids Struct 49(10):1252–1258, 2012). The DEM contact parameters have been calibrated to capture the macroscopic responses and the instability behaviour consistently with the laboratory experiments. The effect of different range of initial states at the beginning of CSD condition such as different initial mean effective stress (p′0p0′), void ratio (e0e0) and deviatoric stress (qq) on the instability behaviour were analysed. In addition, the micromechanical parameters such as coordination number, anisotropic coefficients (geometric, mechanical) have been extracted to assist in characterising the instability behaviour during CSD condition. The initial stress state of the soil (i.e. at the onset of CSD) has shown a significant influence on the evolution of anisotropic coefficients. An increase in geometric anisotropy and a decrease in mechanical anisotropy with time was observed after the instability.