Cyclic Direct Shear Test on Rock Sample with Stepped Structural Plane

Abstract

By conducting the direct shear test on a sample with a stepped structural plane and selecting representative samples for the cyclic shear test under fixed normal stress, the effects of the number (N) of the stepped structural plane, the top length (l1) of the stepped plane and the height (h) of the stepped structural plane on the shearing characteristics and damage morphologies of the specimens were studied. Test results show that: The shear strength of the stepped structural plane and the deterioration index of shear strength are affected by the stress concentration at the corners of the structural plane, the length of the rock bridge, the area and the aspect ratio of structural plane and the ability to resist edge failure of the specimen. When the value of l1 and h is fixed, as N raises from 1 to 5, the shear strength reaches the minimum value at N = 5. Shear failure is transformed into direct shear failure. In the specimen with single stepped structural plane, when the value of h is fixed, as l1 from 10 to 50 mm, the frictional sliding force between the crack surfaces will decrease firstly and then increases with the growth of number of diagonal crack. In the double stepped structural plane specimen, when the value of h is fixed, as l1 from 10 to 50 mm, the shear strength and c increases first then decreases. When the value of l1 is fixed, as h from 10 to 25 mm, the shear strength reaches the maximum value at h = 20 mm. The deterioration index of shear strength was inversely proportional to the number of cyclic shears, which is in turn proportional to N, h, and l1.