Experimental and Numerical Study of the Effect of an Oversize Particle on the Shear Strength of Mined-Rock Pile Material

During in situ direct shear testing on the Questa mined-rock pile material, oversize rock fragments were encountered in the shear box. To study the effect of an oversize particle on the measured friction angles and cohesions, both laboratory and numerical direct shear tests were conducted on unsaturated samples of the rock pile material. In the numerical simulation, a hybrid discrete-finite element method was implemented in which the rock pile material was modeled with discrete particles while the shear box was modeled with finite elements. Both the numerical and physical tests suggest an increase in the measured shear strength of the material due to the presence of an oversize particle in the box. More specifically, the presence of an oversize particle causes an increase in friction angle while cohesion in most situations decreases. The location of the oversize particle along the shear plane was found to be important, as it can modify the failure mechanism.