New peak shear strength criteria for roughness joints

Simulated rock joint samples with different surface topographies are casted by cement paste. A series of direct shear tests under 5 levels of normal stresses, 0.5, 1.0, 1.5, 2.0 and 3.0 MPa, respectively, are performed in order to study the relationship between joint peak shear strength and its three-dimensional surface topography. Effective joint three-dimensional surface mean dip angle and the maximum possible contact area ratio are selected to describe the joint roughness character. Based on the experimental results, a new empirical equation is proposed for these joints by satisfying the peak dilation angle boundary conditions under zero and very high normal stress. Then, new joint peak shear strength criterion is presented. The calculated results by means of the new criterion are compared with the well-known shear strength criteria, such as the Barton’s criteria and Son criteria, and the results show that the Barton’s criteria underestimate the observed peak strength. At last, on the basis of analysis of deviation, the new criterion is also evaluated.