Abstract

Abstract

To study the three-dimensional strength characteristics of rockfill material under an anisotropic state, the anisotropic state variables were introduced into the Mohr-Coulomb failure criterion, and the failure criterion describing the three-dimensional strength of rockfill which was obtained in linear form in this paper. The anisotropic state variables were established with the fabric of rockfill particles. Based on the experimental results of a large triaxial consolidated drained test, fractal dimension theory was introduced to study the relationship between strength and deformation characteristics under different gradation and confining pressures. The experimental results and simulation have shown that: (1) The fractal theory can be used to quantitatively describe the rockfill particles crushing with all kinds of grades under different stress levels. (2) The fabric of rockfill particles was closely related to the three-dimensional strength characteristics. (3) The anisotropic state variables can describe the three-dimensional strength characteristics of rockfill well from a microscopic perspective.

Abstract

Particle breakage plays an important role in rockfill mechanical behaviour. Under compression or shear, the crushing of particles modifies the grain size distribution and indirectly, the material permeability, their frictional properties and the corresponding critical state. In order to study the breakage of individual particles, several approaches were adopted using discrete element method (DEM). Some considered sub-particles joined by bonding or cohesive forces, other replaced particles, which verified a predefined failure criterion, by an equivalent group of smaller particles. In this paper, using the discrete element method, a new methodology was developed. It consisted of modelling crushable rockfill particles using the clump logic, which was responsible for providing a statistical and spatial variability in the strength and shape of the particles. Particle movements and interactions were determined using DEM, allowing to determined the deformation of the rockfill material. Clumps have a major advantage of severely decreasing the number of contact equations to be solved in the model, resulting in less computer time. A comprehensive study of the brittle failure of single-particle crushing tests is presented. Preliminary tests on particle size evolution were also performed, assuming some simplifications. No attempt was made to simulate the real particle size distribution (PSD), due to the cost of simulating smaller particles. Single-particle crushing tests and oedometer tests were simulated using crushable particles, whose results were in agreement with experimental data.