A numerical study of particle friction and initial state effects on the liquefaction of granular assemblies

Abstract

Liquefaction of sandy soil due to cyclic loading can result in catastrophic damage to the built environment. Liquefaction has been previously studied through field testing, laboratory experiments, and numerical simulations. However, the particle-scale behavior of granular materials during the initiation of liquefaction has not been comprehensively quantified. In the current work, the discrete element method is employed to study the effect of global void ratio, initial confining stress, overconsolidation ratio, and particle friction on liquefaction resistance. Mechanical coordination number, local void ratio distribution (LVRD) entropy, fabric anisotropy and average rotational velocity are quantified in each assembly to provide insight into the particle-scale physics governing liquefaction resistance. Results show that lower global void ratio, increased confining stress, higher OCR values, and higher particle friction all increase liquefaction resistance. Immediately prior to the onset of liquefaction, the mechanical coordination number in each assembly sharply decreased to approximately 2.5, with the remaining contacts attributed primarily to particle collision after liquefaction initiation and fabric collapse. Anisotropy induced in the cyclic loading process was due to normal contact force anisotropy, which was more prominent in the specimens with higher initial confining pressures. Liquefaction resistance for overconsolidated specimens was found to be lower than that of normally consolidated specimens at the same void ratio. We observe liquefaction resistance to be sensitive to the coefficient of interparticle sliding friction, especially for lower friction coefficients. Average particle rotational velocities are shown to increase with increasing interparticle friction. The quantity of energy dissipated through frictional sliding was controlled by both the rate of dissipation and the number of loading cycles to liquefaction. In sum, the simulations elucidate significant connections between micromechanical properties and liquefaction response at different initial states and with different particle frictions.