A Laboratory Study Of Seismic Velocities And Attentuation Of Host Rocks For A Nuclear Waste Repository

A number of granitic rock specimens have been studied from the Stripa mine site in connection with a large-scale geomechanics research program. The purpose of the program was to evaluate and develop field and laboratory techniques for rock mass characterization and to determine design parameters for storage of nuclear waste. In this paper a minicomputer-based technique for studying dynamic rock properties in the laboratory is described, together with results from the tests. The specimens were tested under different uniaxial and saturation conditions. Specimens from a field-heated rock mass were also tested to determine if temperatures typical of those encountered with nuclear waste would introduce additional fracturing. Both Vp and Vs increased with stress for both saturated and dry specimens. Both Vp and Vs were higher for saturated specimens at all stress levels compared with the dry. The velocities increased linearly or near linearly with saturation. The test results on the previously heated samples indicate that attenuation is more sensitive to thermally-induced microfracturing than velocities. Analysis of the attenuation values with stress show that rock heated to 200°C is damaged, and that the damage is in form of low-aspect ratio fractures.