Micromechanical Behavior and Modelling of Granular Soil

The goal of this study was to develop a constitutive law for granular soil based on the particulate nature of the material. This is accomplished by a systematic, mostly analytical approach to the problem, starting from the response of the contact between two elastic rough spheres subjected to arbitrary normal and tangential forces, and continuing with the response of regular and random arrays of spheres. The following tasks were completed: a) study and compilation of the differential stress-strain relationships of several regular arrays of identical quartz spheres; b) use of the Self Consistent and Nonlinear Finite Element methods to calculate the small strain, monotonic and cyclic stress-strain behavior of random/regular arrays of identical quartz spheres loaded isotropically and anisotropically, including wave velocity predictions; and c) use of Nonlinear Distinct Element simulations of two-dimensional random arrays of quartz spheres to determine their small and large strain response, including the initial position and subsequent translation and distortion of yield surfaces. The main features of a proposed constitutive law for granular media are discussed. The law is basically the stress-strain equivalent of the force-deformation model for the contact between two spheres, enhanced to incorporate dilation and the distortion of yield surfaces due to prestrain which has been observed in granular media. The proposed stress-strain law includes an infinite number of yield surfaces of conical shape initially parallel to each other.