Proceedings: Mechanics and Mitigation of Violent Failure in Coal and Hard-Rock Mines. Washington, DC: U.S. Bureau of Mines, 1995 May; :323-333
Rock masses in deep mines are subject to high stress, which can result in unexpected, violent failure of rock into mined-out openings. One method to evaluate relative stress is tomographic imaging, a technique based on the principle that highly stressed rock will demonstrate relatively higher velocities than rock under less stress (load). The success of tomography depends on subsequent surveys in which increases, decreases, or changes in locations and magnitude of stress are compared. Researchers at two U.S. Bureau of Mines centers, the Spokane Research Center and the Twin Cities Research Center, have been investigating tomographic imaging as a tool for identifying stress in remnant ore pillars in deep mines. Work has proceeded at two mines, the Lucky Friday Mine, Mullan, ID, and the Homestake Mine, Lead, SD, and two successive tomographic surveys have been completed at each mine. Software has been developed to produce three-dimensional tomograms showing areas of high and low velocities ( stress) in pillars at both mines. Mined-out openings, haulageways, ramps, and crosscuts are areas of low velocity that correlate well to fractured rock and indicate low stress. Areas of higher velocity (therefore higher stress) are well delineated above backfilled stopes.