The influence of asperity deformability on the mechanical behavior of rock joints

• Shear strength of joints increases with increasing deformability of wall material.
• That higher deformability of asperities results in increasing the contact area.
• Young׳s modulus of joint material has been incorporated into constitutive equations.
• Peak shear displacement and shear stiffness also depend on the Young modulus.

The main purpose of this study is to investigate the effect of deformability of joint material on the deformability of rock joints. To do this, replicas of natural rock joint surfaces were constructed using plaster and concrete materials with different values of Young׳s modulus. The replicas underwent direct shear tests with various values of normal stress. The results of 110 direct shear tests show that the deformability of asperities considerably affects normal and shear behaviors of joints. For joints with equal wall compressive strength values, those having higher deformability show higher shear strength. This is due to the fact that higher deformability of asperities results in increasing the contact area during shearing. Based on statistical analyses of the experimental results, the Young׳s modulus of joint material was incorporated into the Barton–Bandis empirical relationships in order to better estimate the peak shear strength, shear stiffness, rate of dilation, and the shear displacement corresponding to the peak.