DEM investigation of particle size distribution effect on direct shear behaviour of granular agglomerates

摘要

Recently, it was proposed that a carefully controlled particle size distribution could potentially change the soil behaviour from well-accepted Critical State framework that was observed in both pure sand and pure clay of uniform sizes to the "transitional" behaviour [1]. As the initial part of the project to identify the reasons contributing the transitional behaviour, a series of 2D Distinct Element Method (DEM) simulations of direct shear box was carried out. The granular material inside the shear box is represented by agglomerates; each of them is formed by strongly bonding three particles together without initial overlapping, but possesses the same contact properties. Different particle size distributions were simulated with the same amount of solid area and initial void ratio. The mechanical shearing behaviour was compared, and the micromechanical reasoning governing the changes of the mechanical behaviour was identified with the help of the computational technique of DEM. The simulated results show that by producing less but stronger force chains than the sample with more fine-size agglomerates, numerical sample with more course-size agglomerates generates higher shear strength and more volumetric dilation. The transitional behaviour, however, is not observed for the assembly of granular agglomerates in this study. Samples sheared under the same confining pressure still reach a unique void ratio, which indicates the existence of the critical state, at large deformation.