Monitoring Ground Movements Near Caving Stopes - Methods and Measurements

摘要

The Bureau of Mines measured rock-mass movements above the undercutting level in a block-caving mine by means of instrumentation installed in drifts and in long drill holes several hundred feet ahead of the approaching panel caving. The instruments included a borehole inclinometer probe to determine the change of profile along a cased drill hole, break-detection cables monitored by time-domain reflectometry to determine the locations of new cracks, multiple-anchor-position extensometers to measure longitudinal ground movements in boreholes, cross-drift extensometer rosettes to measure the amount and direction of deformation in planes normal to the drift axis, and tiltmeters to determine the change of profile along the drift. Off-the-shelf hardware, components, and instruments were incorporated as much as possible, often in innovative arrangements. To assist the prospective user to devise monitoring schemes for specified measurement objectives and to anticipate the problems that will be encountered, installation and operation of the instruments for this application are described in detail and their comparative advantages are discussed. The sensitivity of measurement was great enough to detect ground movements that preceded cracking, although cracking was found to be pervasive to distances of several hundred feet from the caving boundary.