Assessing the Shear Behavior of Oriented Rock Joints under Constant Normal Loading Conditions

Abstract

This paper presents results from a series of constant normal load direct shear tests on artificially created rock joints, in an attempt to quantify the effects of different factors that contribute to the shear strength along “ideal” rock joints. Particular focus is given to the effect of asperity orientation with respect to the direction of shearing. In many historical rock joint shear strength criteria, the effect of a joint’s roughness on the joint shear strength is described based on analysis of only a single profile in the direction of shearing. More recent studies have observed that the distribution of sheared area on a joint surface during shear is significantly affected by the location and distribution of the three-dimensional contact area of the joint surfaces, and results can vary with changes in the asperity inclination angle, the direction of shear, and the applied normal stresses. Results from the current study indicate that the asperity orientation angle has a significant influence on the relative contribution of the contact surface area to the shear strength of a rock joint. In joints with oriented asperities, a combination of vertical displacement (dilatancy) and lateral displacement during shearing was observed. The lateral displacement resulted in a reduction in the magnitude of observed shear-induced dilation of the joint, as well as a reduction in the strength of the joints against the induced shear load. Finally, an alternate approach for describing the shear behavior of oriented rock joints was used to characterize the impact of asperity orientation with respect to the direction of shear on the shear behavior of the rock joint.