Abstract: The shear failure characteristics of rock mass discontinuities are influenced by surface morphology, normal stress and shear history. Close range photogrammetry is a quick and accurate approach to obtain the 3-D morphology of surface features. In this paper, the 3-D surface morphology of the discontinuities is analyzed before and after the multiple normal pressure repeated shear test, and the factors that affect the shear characteristics are analyzed in qualitative and semi-quantitative sense. Results reveal that 1) the influence of morphology on the shear behavior is directional, and only the asperity with the apparent inclination greater than 0 degree could resist each other in the shearing process, but the actual contact surface is quite smaller than potential resistant surface; 2) the effect of roughness on the shear behavior decreases with the increase of normal pressure, and so does shear dilation behavior; 3) the asperity is easily worn and cut even under low normal stress, in particular, asperity with large apparent inclination will be primarily damaged, and peak value of the shear curve does not occur in subsequent shear after the first shear; 4) friction angle increases with the decrease of positive pressure, while cohesion displays an opposite trend; 5) the shear strength parameters fitted from the first residual value and the subsequent shear strength value can be used to represent the shear strength of the discontinuities with the shear movement history.

Key words: rock discontinuity, 3-D morphology, direct shear test, close range photogrammetry, shear strength