Micromechanical insights into grading effects on cyclic liquefaction resistance of sands

This study investigates the micromechanical interpretation of grading effects on the cyclic liquefaction resistance of sands using discrete element method simulations. Three-dimensional granular assemblies with varying coefficients of uniformity were prepared in loose and medium-dense states using two distinct preparation protocols and subjected to constant-volume cyclic simple shear under a range of cyclic stress ratios. Cyclic liquefaction resistance was quantified as the number of loading cycles required to reach initial liquefaction. To interpret the observed trends, a micromechanical measure based on the rate of decline in mechanical coordination number during the pre-liquefaction phase is introduced. Across all relative densities considered, grading exhibited a non-monotonic influence on cyclic liquefaction resistance. In contrast, post-liquefaction shear strain accumulation decreased monotonically as the coefficient of uniformity increased. A strong power-law relationship was identified between liquefaction resistance and the rate of pre-liquefaction contact degradation across all studied assemblies. These findings suggest that the evolution of contact loss prior to liquefaction provides a useful micromechanical framework for interpreting grading effects on cyclic liquefaction resistance within the DEM simulations examined.