Abstract: Among the existing literature on shear mechanical properties of rock discontinuities, there are more researches on simple discontinuities than those on natural discontinuities, and more researches on mechanical properties evolution than those on geometric evolution. In this study, rock discontinuities in nearly natural forms are prepared through the Brazilian splitting test, and the splitting samples are produced with simulated materials. Then under cyclic loading, the shear property evolution laws and influencing factors of rock discontinuities are studied. The influences of normal stress, number of shear cycles, rock wall strength and roughness of rock discontinuity surface on mechanical properties and morphology of rock discontinuities under cyclic shearing are analyzed. Finally, by introducing the negative exponential deterioration parameter related to the number of shear cycles (Nd) into the adhesion theory of friction-Barton empirical formula, a formula for cyclic shear strength of rock discontinuities is proposed. The results show that with the increases of normal stress, rock wall strength and roughness of rock discontinuity surface, the maximum shear stress of rock discontinuities increases; with the increases of normal stress, number of shear cycles and roughness of rock discontinuity surface, the rock wall strength decreases and thus the normalized roughness parameters of rock discontinuities reduce. The proposed cyclic shear strength formula verifies the test results and provides a theoretical reference for engineering safety design.

Key words: rock discontinuities, cyclic shearing, mechanical property, topographic characteristics, reverse engineering