Abstract

In this study, the effects of shear rate on the mechanical behaviors of artificial rock joints with regular asperities have been studied by a series of double-shear tests. The adopted simulated material composed of gypsum, quartz sand and water was used to simulate rock joints with regular asperities 0°, 15° and 30°. A number of double-shear tests were performed by using a material testing machine (MTS 819 High Rate Test System) and the rate of shear displacement was controlled in the range of 10–2–101 mm/sec. A set of the artificial rock joints contained two sliding surface and was tested under constant normal load (CNL) boundary condition, and the range of normal stress was 0.1–0.7 (MPa) applied by a pair of pneumatic cylinders. Experimental results show that the shear displacement curves exist obvious stick-slip phenomenon especially in low shear rate and high normal stress for smooth rock joints. The shear stiffness of the smooth joints normalized by normal stress has a semilogarithmic linear relationship with normalized shear rate. The dilation angle is decreasing with the increasing of normal stress level, and the decreased tendency is evident especially at asperities 30°; however, the trends of dilation angle varied with shear rate are different with asperities 15° and 30° as a result of varieties of failure modes. The increasing tendency of the slope of shear strength envelopes is related to the raising of shear rate. In order to distinguish the influences of normal stress level and shear rate on the failure of regular asperities, the failure area ratio (FAR) is defined as the area ratio of shearing failure part and pre-shearing surface. It is found that the FAR has a tendency to increase with the raising of normal stress level but exist no obvious relation with shear rate.

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