RESEARCH OF ROCK FAILURE TESTING UNDER COMBINED SHEAR AND TENSION

Tension and shear fracture form of rock is under special stress state,that is under the normal tension stress perpendicular to the failure surface and shear stress parallel to rupture surface. Using the self-developed DSC-800 rock tension and shear apparatus with electro-hydraulic servo,we conducted plenty of tension and shear tests of granodiorite and sandstone; carried out corresponding three-dimensional laser scan of fracture surface,SEM,rock physical and mechanical properties tests,PFC numerical modeling tests,etal. Then studied the features of rock tension and shear fracture surface using fractal theory; got the whole fracture criterion of rock from tension-shear area to compression-shear area; analyzed the influences of rate of shear to rock tension and shear strength; studied the process of rock failure under tension and shear using PFC.Research conclusions are as follow:(1)Macro and micro fractal dimension(roughness) of the fracture surface increase with the increase of tension stress.(2)Micro fracture pattern of rock is combination of tension fracture and shear fracture. Micro fracture pattern is mainly about shear failure when tension stress is small; the tension failure is distinct gradually as tension stress increases.(3)Tension stress and shear stress have linear negative relationship in tension shear area. Line slope in tension shear area is greater than that in compression shear zone,and rock is more easy to fracture in tension shear area.(4)Under the condition of tension and shear,shear rate and shear strength have nonlinear inverse relationship. With the increase of shear rate,roughness of rock tension shear fracture surface increases.(5)Establish PFC numerical test model of rock under tension and shear stress to simulate force chain evolution in the process of rock fracture and the influence of shear rate on the roughness of tension shear fracture surface,and get the same results as laboratory tests.