A new three-dimensional peak shear strength criterion of rock joints considering true-sheared asperities

The shear resistance between contacting rock surfaces under normal confinement is governed by the asperities truly involved in shear, i.e., true-sheared asperities. However, the prediction of joint peak shear strength considering mechanical contributions of true-sheared asperities remains unresolved. Here, we developed a three-dimensional (3D) peak shear strength criterion by independently quantifying dilation and shear-off of true-sheared asperities. The true-sheared asperities were predicted by identifying the asperities with initial apparent dip angles exceeding the evaluated peak dilation angle that was a function of the real contact area ratio and 3D morphological parameters. The real contact area ratio was quantified by the nonlinear reduction of the global joint aperture that is predictable via the statistical distribution of local apertures of joints. Subsequently, the shear area ratio and associated shear-off component were determined by evaluating the shear-off portion of the true-sheared asperities. The new criterion was validated against experimental measurements on the peak shear strength of both natural and artificial joints. The input parameters involved in this criterion are readily acquirable from morphological properties and normal deformability of joints. Therefore, it potentially can serve as a fast and convenient shear strength assessment method for natural rock joints that may complement conventional shear experiments.