Influences of Joint Persistence on the Compressive-Shear and Tensile-Shear Failure Behavior of Jointed Rock Mass: An Experimental and Numerical Study

The non-persistent jointed rock mass is prone to compressive-shear and tensile-shear failures. Tensile-shear failure has been studied less than compressive-shear failure. This study develops a new shear test apparatus for cubic rock specimens to explore the tensile-shear failure of jointed rock mass under varying joint persistence and compare it to compressive-shear failure. The jointed rock specimens are sheared and monitored using acoustic emission (AE) equipment, an infrared thermal imager, and a high-speed camera to track stress, AE signal, temperature, and deformation. Based on the test results, RFPA(2D) numerical simulation is conducted to investigate the effect of joint persistence on the compressive- and tensile-shear strength of the rock bridge. Tensile- and compressive-shear stress curves differ greatly. The former may have several stress peaks and peak AE count time does not equal peak strength time. The rock specimen's compressive-shear strength is far higher than its tensile-shear strength, but tensile-shear tests accumulate more AE counts and energy. Tensile-shear failure has a large crack opening and rapid temperature progression. The rock specimen cools before peak strength, which is the opposite of compressive-shear failure. The two tests differ significantly regarding crack development and deformation evolution. The shear strength of the specimens in the compressive-shear and tensile-shear tests decreases approximately linearly as joint persistence increases, and the shear strength of the rock bridges increases and then decreases. Previous research showed that increasing joint persistence increases rock bridge cohesiveness. At relatively high joint persistence, however, the considerable cohesion weakening of the rock bridge caused by tensile cracks near the joint tip should be considered. The findings could contribute to a better understanding of the failure process of jointed rock mass under compressive-shear and tensile-shear stresses.