The critical state of crushable granular sand

The concept of critical state has been a cornerstone of modern critical state soil mechanics. It remains inconclusive how grain crushing affects critical state behavior in crushable granular sand. A multiscale computational approach is employed in this study to simulate the shearing behavior of crushable granular sand at critical state. Grain crushing is rigorously considered by preserving the co-evolutions of grain size and shape in the simulation of the shearing process. Systematic simulations on specimens with varying initial states and loading paths show unique characteristics of critical state for crushable granular sand in terms of critical state stress ratio, void ratio, breakage index, and shape descriptors which are independent of stress path and initial conditions. To further understand the deformation mechanisms of crushable sand at critical state, the volumetric strain is decomposed into three components due respectively to grain size reduction, the interlocking of irregular shaped grains generated by crushing, and inter-particle friction. Competing mechanisms among the three strain components are quantitatively analyzed and discussed. Initial void ratio and stress levels are found to play a prominent role in shaping the critical state deformation of crushable sand and such impact may be gauged through the fraction of grains that experience crushing.