A New Empirical Peak Shear Strength Criterion for Rock Joints

ABSTRACT: The paper presents findings of an experimental as well as theoretical/analytical research initiated (a) to quantify joint surface roughness on a plane and then (b) to develop a new peak shear strength criterion for rock joints which has the capability of capturing the anisotropic behavior of peak shear strength due to the anisotropy of joint surface roughness. The results show clearly that at least two parameters are required to quantify joint roughness in one dimension. By limiting to only statistical parameters, an average slope of the profile (average I angle) is suggested to quantify the large scale undulations of the profile (non-stationary part of the profile) and the root mean square of the slope (z₂') is suggested to quantify the small scale roughness of the profile (stationary part of the profile). In order to capture the anistropic roughness, it was found necessary to calculate both averages I and z₂' in different directions on the joint surface. The shear strength results of a model material joint show that the suggested new equation, which is based on very limited experimental data, has a good capability of predicting the anisotropic peak shear strength of the joints.