The interaction of stress wave and rock joints is crucial in rock engineering to assess the stability and damage of underground structures under dynamic loads. Since stress waves generally, obliquely impinge to the rock joints, analysis of the oblique interaction is of special interests to mining engineers, seismologists and geoscientists. Wave propagation across an interface of two elastic media has been analyzed in detail by Kolsky [1 ] to calculate the reflection and transmission coefficients, by using a simple harmonic wave in the particle movement equation and Hooke's law. Based on the wave motion theory and the principle of conservation of momentum, the mechanism of longitudinal- (P-) and shear- (S-) waves propagating across an interface between the two media has been described by Johnson [2]. The above two studies established the relation between the wave propagation velocities and the angles of the incident, reflected and transmitted waves for a free boundary and welded interface. However, the natural rock joints are generally non-welded, large in extent with void spaces and asperities of contact, and have relative displacements (opening, closure and slip) under normal and shear stresses [3-7].
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