Abstract: The morphology parameters proposed by Grasselli fully described the three-dimensional roughness of rock joints. Based on Grasselli’s three-dimensional parameters, Xia et al, Yang et al, and Tang et al developed new peak shear strength models. It is revealed that Xia’s model didn’t agree well with the boundary conditions. Yang’s model can not explain the mechanism of tensile failure during the shearing of rock joints. Tang’s model showed a low accuracy in predicting the peak shear strength of a rock joint. In light of these problems, a new peak shear strength model is established. The new model is verified based on the 63 groups of rock joints published by Grasselli, Tang and Yang, the results show that the new model has the same accuracy with the published model, and the new model is simple in terms of form so it can provide a reference for rock engineering. Besides, it will improve the accuracy in predicting the peak shear strength between the calculated results and the test results when the relationship function f(?n) takes the morphological parameter into consideration.

Key words: rock joints, peak shear strength model, Grasselli’s model