ACOUSTIC VELOCITY IN LAYERED ROCK MASSES WITH PERIODIC FRACTURES

Fractures and layering in rock masses have a large impact on both the mechanical and hydraulic properties of the rock mass. When considering seismic elastic waves, fractures can also trap and guide waves and the behavior of such waves may prove useful for probing the geometrical and mechanical properties of the fractures. In the long- wavelength limit, when the size of the seismic wavelength is much larger than the layer and/or fracture spacing, the propagation velocity is obtained by the effective medium theory. However, when the wavelength becomes smaller, a dispersive behavior is obtained that may be significantly affected by the layer and fracture spacing. In the proposed paper a dynamic homogenization technique proposed by the Authors to analyze dispersive waves in periodic elastic materials (Bacigalupo & Gambarotta, 2012) is revised and extended to the analysis of dispersive waves in periodically layered fractured rock masses. The obtained results for some material meso-structures by means of the proposed approach are compared to those ones by the rigorous Floquet-Bloch theory. Finally, some examples representative of rock masses are presented and discussed.