Effective velocity of reflected wave in rock mass with different wave impedances of normal incidence of stress wave

The effective velocity of the reflected wave in rock mass is of significance to the detection of crustal structure and the geophysical seismic exploration. In this paper, the modified characteristic method was introduced to solve P-wave reflection in rock mass with different wave impedances on two sides of the joint. Effective velocity was defined to characterize the propagation velocity of the reflected wave in jointed rock mass. The effects of incident frequency, joint stiffness and wave impedance ratio on the effective velocity were discussed. The results show that when the stress wave propagation in "hard-to-soft" rock mass, the effective velocity increases firstly and then decreases as the incident frequency and the joint stiffness increase, while the effective velocity always decreases as the wave impedance ratio increases; when the stress wave propagation in "soft-to-hard" rock mass, the effective velocity decreases as the incident frequency increases, increases as the joint stiffness increases and decreases as the wave impedance ratio increases. The wave impedance ratio has an important influence on the effective velocity. The effective velocity without considering wave impedance ratio is smaller than that of stress wave propagation in "soft-to-hard" rock mass, but larger than that of stress wave propagation in "hard-to-soft" rock mass.