Variations in shear behavior among specimens with different packing patterns

This paper describes variations in shear behavior among specimens with the same packing fraction but different coordination number (different packing patterns). The multi-sphere models to express grain shapes of Toyoura sand were employed in discrete-element method (DEM) simulation. Specimens with different packing patterns were produced by two methods: changing interparticle friction angle (FC method) and applying cyclic simple shear (CC method). A series of simple shear DEM simulation was carried out using the FC and CC specimens. The shear response in small strain range (secant shear modulus) of FC was larger than CC specimens, while difference in peak shear stress (bulk shear friction) between FC and CC specimens were insignificant. Strong correlation was found in the relation between secant shear modulus and coordination number of the system, as well as between the bulk shear friction and packing fraction. The initial coordination number rapidly decreases with increasing shear strain, and thereafter it reaches an isostatic value. On the other hand, the packing density required large shear strain for reaching the critical state. It was found that the initial difference in coordination number between FC and CC specimens disappeared before reaching their bulk shear frictions. Therefore, the bulk shear friction strongly correlates with the packing density.