Abstract
Underground mines commonly use drill core rigs to anticipate future ground conditions. These drill core rigs can be highly expensive and can easily miss changes in rock characterization, depending on the amount of drilling taking place. In an attempt to provide a more efficient means of determining changes in rock characterization, a study was conducted using the Refraction Microtremor (ReMi) process in an underground mine. ReMi involves acquiring noise data along a linear array of geophones. Data is processed to obtain shear-wave velocities underneath the array. The data for our study was collected at an underground gold mine in Nevada, and was analyzed using the SeisOpt® ReMi™ (© Optim, 2015). The data was collected using horizontal and vertical geophones, placed into the ribs of the drift in a horizontal plane, rather than the industry standard placement of vertical geophones into the ground in a vertical plane. In order to determine whether the changes seen actually exist, shear wave velocities were measured in location of known rock characterization. These shear wave velocities were then compared with the Rock Mass Rating (RMR) and previously published correlations between RMR and shear wave velocity. This comparison yielded results that did not match the published correlation between RMR and shear wave velocity. It is likely that the stresses surrounding the excavation affected the shear wave velocity values recorded; however, it is difficult to quantify these affects due to minimal research regarding in-situ stresses in the area. In addition, the use of ReMi as a tool to determine the extent of voids underground was investigated. This can then be used to determine the extent of voids underground and help to distinguish locations where voids may be near above or below excavations. The recordings showed that a void existed, however, did not show the entire extents of the void. This is because the geophone array was not long enough to cover the full length of the void. In order to determine if the ReMi process can effectively be employed to detect voids into the rib, further research is suggested.
