| Abstract: | Results are presented of a series of cross-hole acoustic measurements made between four horizontal boreholes drilled from a near-surface underground opening situated in a basaltic rock mass. The objectives of the program were to assess the extent of blast damage around the opening, and to evaluate the rock mass characteristics and their spatial variation around the opening. The acoustic velocity and attenuation data are indicative of an anisotropic, jointed rock mass, with a greater intensity of jointing along travel paths in the horizontal than the vertical direction. Low acoustic P- and S-velocities are indicative of blast damage and of zones of intense jointing or fracturing. In this case blast damage extends to approximately 1.5 m from the face. Attenuation data appear to be less sensitive in distinguishing between the blast-damaged zone and intense vertical jointing and fracturing in the virgin rock mass. Taken together with field data, laboratory measurements of P- and S-wave velocities on intact core samples suggest that the rock mass is probably water saturated. |
