Effect of Nonstationarity on Shear Properties of Rock Joints and a New Peak Shear Strength Criterion

In rock masses, there might be structural nonstationarity in the joint morphology that influences the shear behavior of rock joints. However, research into this effect is seldom reported. In this study, shear tests on artificial rock joints that contained stationary morphology and different nonstationary features were conducted. The experimental results showed that nonstationarity has a significant effect on the shear properties of rock joints. Under the action of lower normal stress levels, the peak shear strength of joints increased with the increase in the nonstationary angle, and it was easy for the slip behavior along the nonstationary trend to occur. Under higher normal stress levels, the damage to big areas in the upper and lower joint blocks, especially on the left and right ends of the joint surfaces, readily appeared. In this case, the nonstationary characteristics tended to be the main factor that controlled the damage to joints. The analysis revealed that after subtracting the nonstationary angle, the peak friction angles of the joints with nonstationarity were close to the peak friction angles of the joints with stationary morphology and provided the same normal stress. Therefore, the nonstationary angle and stationary joint morphology were separately but fully considered to describe the peak dilatancy angle. Using the proposed model for the peak dilatancy angle, a new criterion for the peak shear strength of joints that contained nonstationary features was established. Comparisons of the new criterion with the published criteria when estimating the peak shear strength of rough rock joints showed that the new criterion has a good prediction accuracy for rock joints with nonstationarity.