A technique for processing seismic data has been developed that provides a ‘representative velocity’ tomogram which may be interpreted in terms of the engineering properties of the subject rock mass. This transmission system is intended for use in cross-borehole surveys and has been successfully tested between sub-parallel mine roadways in a massive granite body.
The velocities of compressional waves between numerous source and transducer locations are analysed, and the interactive character of the observations is used to build a two-dimensional array of computed ‘representative velocities’ appropriate to specific areas within the intervening rock mass. Evaluation of the processed data is undertaken using site-specific and more general rock mass classification systems. The processing is carried out on a CBM Pet microcomputer and the program is readily adaptable to most field configurations. The program also allows various mapping and influence parameters to be varied and optimized to obtain the best resolution of rock mass inhomogeneities.
Fast Fourier transform routines for the calculation of the energy spectral density (and other frequency domain functions) of ground vibrations are also briefly discussed.