Experimental Study on Peak Shear Strength Criterion for Rock Joints

The three-dimensional (3D) morphology of a rock joint has a great impact on its shear behavior. To study the relationship between the 3D morphological characteristics and the peak shear strength, several tilt tests were conducted on four groups of tensile fractures and direct shear tests were carried out under different constant normal loads (CNL). The normal load ranges from 0.325 to 8.0 MPa. In this study, fresh tensile fractures which were splitted from granite and sandstone samples were used. The morphology of each tensile fracture was measured before direct shear tests. A new peak shear strength criterion for rock joints is proposed using two 3D morphological parameters which are termed as the maximum apparent dip angle θmax∗\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\theta_{\max}^{*}$$\end{document} and the roughness parameter C. The calculated peak strengths using the proposed criterion match well with the observed values. In addition, a comparison of the proposed model with the Grasselli’s model (2003) and Xia’s model (2014) shows that the proposed model is easier in the form and gives a rational improvement. At last, direct shear test data of tensile fractures which are collected from Grasselli (2003) are used to verify the proposed model. It is seen that the proposed model has a reliable estimate of the peak shear strength of tensile fractures and presumably for rock joints.