Liquefaction of granular materials in constant-volume cyclic shearing: Transition between solid-like and fluid-like states

By means of 3D-DEM cyclic simple shear simulations at constant volume, this paper analyzes the evolution of the internal structure during cyclic liquefaction of dense granular media. Upon liquefaction, the granular system undergoes a fast transition to a regime where the fluid-like shear strain develops. This regime is characterized by low shear modulus, decreasing dilatancy, and reduced shear viscosity. We analyze the internal structure by means of several micro-and meso-scale descriptors, including coordination number, fabric anisotropy, number of clusters, a fraction of maximum cluster size, and a percolation index. We select a typical post-liquefaction cycle in which we highlight several particular states that naturally divide the cycle into different periods. During liquefaction, the system deforms significantly with an enhanced number of binary collisions initially and particle clusters subsequently. Both the coordination number and percolation index increase while fabric anisotropy oscillates. The fluid-like to solid-like transition is characterized by a well-defined value of the coordination number (3.6) when the particles percolate across the system. From the analysis of the micro -and meso-scale behaviors, we further discuss two possible criteria for exiting the fluid-like state based on the excess pore pressure.