Mining applications of crosshole seismic tomography.

摘要

Applications of two-dimensional crosshole seismic tomography to problems in hard rock mining are investigated through the analysis of three case studies.;The second field study comprises the analysis of 14 tomographic data sets. The mean velocities are found to fluctuate as much as 260 m/s, and are shown to have standard deviations of less than 30 m/s, generally less than one-half of one percent of the rock mass velocity. The shapes of mean velocity versus time plots for each of the two image planes track each other well. The rock mass is found to be anisotropic, with percentage anisotropy in excess of ten percent. An attempt is made at "correcting" the data for the anisotropy such that an isotropic inversion scheme may be employed.;The experimental finding that variation in compressional wave velocity may be accurately monitored in a rock mass on a large scale is significant. Observation of variation in velocity, in response to local excavation, carries the potential for rock mechanics interpretations that could increase understanding of the behaviour of large rock masses under time varying load. In this case study variations in compressional wave velocity are attributed to changes in "rock mass quality" resulting from changes in the local stress regime.;The third case study is an attempt to produce tomographic attenuation images from a crosshole data set. This goal is not achieved due to significant compressional wave attenuation anisotropy at the field site, in spite of a lack of compressional wave velocity anisotropy. (Abstract shortened by UMI.).;The first field study is an attempt to image a steeply dipping low velocity zone (estimated as 4500 m/s) in a higher velocity background (greater than 6000 m/s) using a three-sided acquisition geometry. Indications of the low velocity zone are produced in the final image. Mapping of lithological boundaries is estimated to have a resolution of approximately five to ten percent of the nominal survey dimension which, in this case, was on a 40 m x 50 m rectangular plane.