Effects of Particle Shape and Microstructure on Strength and Dilatancy During a Numerical Direct Shear Test

ABSTRACT: Discrete element method offers insights into the soil behaviour at the microscopic level. In this investigation, a series of numerical direct shear tests is carried out by a three-dimensional discrete element code PFC. The size of the shear box is 6 cm long, 3 cm wide and 4 cm high. Non-spherical shaped particles are created by joining primary constitutive spherical balls together with the aid of the built-in clump logic in the code. Particles of three different aspect ratios (defined as length/width of a particle): 1.0, 1.5, and 2.0, are generated and studied in this paper. The box is filled with particles by the deposition method. By controlling the friction among particles as well as the direction of deposition, particle assemblies with very similar density but different microstructures before shearing are obtained. The deformational characteristics of the particle assemblages are studied at both microscopic and macroscopic level. The effects of particle shape and microstructure on the assemblage’s strength and dilatancy are studied and discussed. It is found that assemblages with elongated particles give slightly less dilative response in general. Microstructure, however, have a strong influence on the shear strength. Evolution of microstructures is also investigated and the results show that the change in particles’ major axis at the end of shear is insignificant.