The effects of joint spacing on transmission characteristics of stress waves through layered composite rock masses

The effects of joint spacing on the transmission characteristics of stress waves through layered composite rock masses were investigated. First, a model of layered composite rock masses containing multiple parallel joints with different media in front of and behind the joints was introduced to study multiple reflections between joints. Second, wave transmission through layered composite rock masses was investigated and compared with wave transmission through traditional layered homogeneous rock masses. Finally, the effects of joint spacing and wave impedance ratio on particle velocity transmission coefficient were discussed. The results indicate that for wave propagation through rock masses with the same joint spacing, the onset time and amplitude of the transmitted wave in layered composite rock masses are smaller than those in layered homogeneous rock masses. For wave transmission through rock masses with the same nondimensional joint spacing, the onset time of the transmitted wave in the layered composite rock masses is similar to that in the layered homogeneous rock masses, while the amplitude of the transmitted wave in the layered composite rock masses is smaller than that in the layered homogeneous rock masses. In addition, the particle velocity transmission coefficient first increases and then decreases to be constant as the joint spacing increases, while it continues to increase as the wave impedance ratio increases for wave transmission through both layered composite rock masses and layered homogeneous rock masses.