Dynamic response of a rock fracture filled with viscoelastic materials

Rock fractures filled with viscoelastic materials, such as sand, usually contribute to rock mass instability under the influence of seismic waves and dynamic loads. The purpose of this study is to verify that the specific fracture stiffness and the specific initial mass of the filling sand are two key fracture parameters in interrelating the physical, mechanical and seismic properties of a rock fracture filled with dry sand. A series of dynamic tests using a split Hopkinson rock bar was conducted on a simulated sand-filled fracture. The experimental results show that stress wave attenuation across the filled fracture is strongly affected by wave reflection and transmission at the fracture interfaces and the dynamic compaction of the filling sand. With the comparison between the analytical predictions by the displacement discontinuity model and the displacement and stress discontinuity model and the experimental results from the laboratory tests, it is found that both models can predict a filled fracture with a smaller thickness (i.e., less than 10. mm). The displacement and stress discontinuity model may be used to predict a fracture with a larger thickness by considering the specific initial mass of filling materials. The wave transmission coefficient for a filled fracture generally increases with increasing specific fracture stiffness.