ABSTRACT
Wave propagation across one single joint has been extensively studied (Schoenberg 1980, Pyrak-Nolte et al. 1990, Gu et al. 1995, Pyrak-Nolte 1996, Zhao & Cai 2001). However, compared with wave propagation across one joint, wave propagation across one joint set will be more complicated due to multiple wave reflections among the joints. Some researchers (PyrakNolte et al. 1990b, Myer et al. 1995) tried to ignore the multiple wave reflections as an approximation. However, laboratory experiments (Pyrak-Nolte et al. 1990b, Myer et al. 1995, Hopkins et al. 1988) found that the simplified method was valid only when the first arriving wave was not contaminated by multiple wave reflections. When incident wavelength is comparable or larger than the joint spacing, the simplified method is not applicable, as transmitted waves generated by multiple wave reflections among the joints have great effect on the amplitude of the transmitted wave. Combined with the DDM, method of characteristics has been used to study wave propagation across one joint set in order to take into account multiple wave reflections (Cai & Zhao 2000, Zhao J. et al. 2006, Zhao X.B. et al. 2006a, Zhao X.B. et al. 2006b). In those studies, the responses at certain time can be derived by those at previous time. Combined with equivalent medium model, Li et al. (2010) has introduced a new concept of virtual wave source (VWS) to study wave propagation across one jointed rock mass. In the study, VWS exists at the position of each joint surface
in the equivalent medium, i.e. the jointed rock mass. And VWS produced new waves at each time when an incident wave propagated across the joint. Then the transmitted wave can be derived using the obtained effective moduli and waves produced by VWS.
