Experimental study on stress wave interaction with rock fractures

A split Hopkinson rock bar is developed and utilized to characterize the interaction between stress wave and artificial rock fractures. The non-filled contact fracture is assumed to be the direct contact interface between the incident bar (rear end) and the transmitted bar (front end), while the filled fracture is simulated by inserting a layer of filling materials, e.g., sand and clay, in the opening at the interface of two bars. The experimental results show that the non-filled contact fracture displays stress equilibrium and displacement discontinuity, however, the filled fracture exhibits stress and displacement discontinuities. The transmission coefficient for the non-filled contact fracture increases with higher loading rate. The filled fracture displays lower strength and larger deformation than the non-filled contact fracture, which likely induces the instability of rock masses. The transmission coefficient for the filled fracture decreases with increasing thickness of the filling materials, and the transmission coefficient for the sand-filled fracture is larger than that for the clay-filled fracture. It is found that stress wave attenuate much highly due to the large fracture aperture and the low stiffness filling materials.