Assessment of Roof Stability and Secondary Support Requirements in the United States Operations

ABSTRACT: This paper reviews case studies of underground mine instrumentation and tomography in coal and evaporate mines, and threshold magnitude of roof deformation and wave velocity to determine secondary support requirements. Measurements of amount and rate of roof deformation have been extensively used in in the United States coal mines. The rate of roof movement is a good indicator of roof stability, because it indicates a change in the stability of the whole mining system. A change from a steady rate of movement to a high (critical) rate can indicate roof block detachment, loss of support effectiveness, roof shearing by pillars, or impending pillar failure. Selected results from a comprehensive case study is presented here to show the application of the tomographic techniques for assessing changes in structural stability in a trona mine where tomographic surveys were complimented with deformation measurements and fracture mapping. Significant changes in seismic wave velocities (17%), amount of roof separation (60 mm), and number of roof fractures occurred during the monitoring period requiring secondary support installations.