Evaluation Models for the Peak Shear-Strength and Shear-Resistance Components of Rough Rock Joints

摘要

This study aims to present a new model for evaluating the peak shear strength of rock joints and investigate the contribution from different shear components to the total shear resistance. Direct shear tests under constant normal load (CNL) conditions were performed on artificial rock joints with different morphology. Before the shear test, a 3D optical scanner was used to measure the joint morphology, and then two statistical parameters were suggested to characterize the joint roughness. For establishing an evaluation model of peak shear strength of rock joints, a model of peak dilatancy angle was first developed and then incorporated into the Maksimovic criterion. A new peak shear strength model for rock joints was thus established, and a good evaluating precision of the new criterion was found by comparing predictive results with experimental results. Three shear strength components, i.e., basic friction, dilation, and shear-off of asperities were investigated. Results show that the basic friction represents over 50 % of the total shear resistance, and this proportion grows steadily by increasing the normal stress. As the normal stress increases, the percentage of shear-off rises gradually before approaching a stable level, whereas dilation consistently decreases. At a certain normal stress level, the basic friction of joints with a lower roughness makes up more of the contribution to the total shear strength, whereas the shear-off component tends to be greater on rougher rock joints. However, the dilation of joints with different roughness does not show an obvious difference in terms of proportion. The apparent cohesion of sheared rock joints increases as the normal stress increases. The rock joint with a rougher surface has a larger apparent cohesion at a certain normal stress level.