Updates to Grasselli’s Peak Shear Strength Model

The morphological characteristics of rock joints have a significant impact on the peak shear strength of a rock mass. In this study, three-dimensional scanning tests have been conducted on 39 joint specimens. Based on the scanning data, the morphological parameter \( C^\prime \) has been developed to describe the joint roughness. With an explicit physical meaning, this index is negatively correlated with the joint roughness and can reflect the anisotropy of surface morphology. Using a newly developed derivation method, the morphological parameter \( C^\prime \) of each joint from the earlier studies has been determined. The scanning test results in this study have been used to confirm the feasibility of this new derivation method. By applying the least square fitting method to the Grasselli’s (Shear strength of rock joints based on quantified surface description. Dissertation, Swiss Federal Institute of Technology, 2001) test results, a new peak shear strength model has been developed. Finally, a comparison of the peak shear strength of rock joint predicted by the new model and other classic models shows that the new model, characterized by simplicity, relatively higher precision, and a definite physical meaning, is feasible to predict the peak shear strength of rock joints.