Numerical modeling of plane wave propagation characteristics in viscoelastic jointed rock masses

The investigation of two-dimensional plane wave propagation in viscoelastic jointed rock masses constitutes a crucial aspect of studying far-field blast stress wave transmission. A typical numerical model was established using ANSYS/LS-DYNA, where the wavefront was parallel to the viscoelastic joint plane. By defining the relative position of measurement points along the rock mass minor axis as d/L, amplitude attenuation on the wavefront and transmission/reflection coefficients were analyzed. Differences in wave propagation characteristics between models with closed unfilled joint and viscoelastic joints were compared. The influences of impact velocity and joint thickness on transmission and reflection coefficients were examined. Results indicate that the spatial uniformity of plane wave amplitude distribution relative to the wavefront diminishes with increasing propagation distance. While the incident wave amplitude (I), transmitted wave amplitude (T), and reflected wave amplitude (R) all decrease with increasing d/L, their differing attenuation rates lead to distinct spatial variations in the transmission coefficient (T_c) and reflection coefficient (R_c). Overall, T_c exhibits a slowly oscillatory decay, whereas R_c initially shows minor fluctuations before decreasing rapidly to its minimum near d/L=1. Compared to closed unfilled joint, the viscoelastic joint model exhibits smaller T and T_c values but larger R and R_c values, demonstrating that viscoelastic joints hinder transmitted wave propagation. Increasing impact velocity generates incident waves with higher frequencies, increases the directional attenuation rate along the propagation path, and reduces both T_c and R_c, while simultaneously reducing spatial variations in incident wave amplitude (I). As joint thickness increases, the hindering effect of joints on wave propagation intensifies, resulting in a significant reduction in T_c, while the change in R_c remains comparatively minor.