Role of filling materials in a P-wave interaction with a rock fracture

a r t i c l e i n f o The purpose of this study is to investigate the role of filling materials (e.g., quartz sand and kaolin clay) in the interaction between a P-wave and a rock fracture. The specific fracture stiffness reflects the seismic response of a filled fracture, while the wave transmission coefficient describes P-wave transmission across the filled fracture. A series of experimental tests using a split Hopkinson rock bar technique are conducted on artificial rock fractures that are filled with pure quartz sand, sand–clay mixtures with 30%, 50% and 70% clay weight fractions, and a pure clay matrix. The boundary conditions of the filled fracture, i.e., the displacement and stress discontinuities, are used in the method of characteristic lines to calculate the wave transmission coefficient in the time domain. The analytical results agree well with the experimental results. The specific fracture stiffness and the wave transmission coefficient decrease with increasing filling material thickness. When the clay matrix completely fills the void space of the quartz sand, the filled fracture exhibits the largest specific fracture stiffness and promotes P-wave transmission. In general, the wave transmission coefficient is strongly related to the specific fracture stiffness, regardless of the filling material composition or the filling material thickness. When seismic waves propagate through rock masses, rock fractures attenuate the wave amplitude and decrease the wave velocity. Natural fractures are often filled with weak materials, e.g., sand and clay. These filling materials and their mixtures influence the mechanical and physical behaviors of rock fractures, such as strength, porosity and permeability (Crawford et al., 2008). During seismic wave propagation across a filled fracture, wave attenuation is mainly determined by the dynamic compaction of filling materials and by wave reflection and transmission at fracture interfaces (Wu et al., 2013a,b). The seismic response of a filled fracture, such as opening and closure, may induce rock mass collapse. The interaction between a P-wave and a filled fracture is thus important to assess seismic energy radiation and rock mass instability. A previous study (Wu et al., 2013c) investigated the effects of the fracture thickness, the particle size of the filling sand and the loading rate of an incident wave on the dynamic properties of a filled fracture. The fracture properties and the loading conditions affect the dynamic compaction of filling materials. The dynamic compaction also depends on filling material types. For instance, when a …