OFR-114-85 Development Of A Roof Competence Tester

MESA Corporation has completed a four-year program for the Bureau of Mines to develop a technique for measuring roof competence in underground coal mines. The preferred technique employs a tracer gas that is injected into a roof borehole drilled near the working face. The tracer gas performs the dual purpose of determining the pressure loss rate from the borehole and of marking the diffusion pattern of the the escaping gas. The primary detection technique relies upon observation of the rate of pressure drop in a hole drilled in the roof strata under test. If this measurement indicates a significant probability of roof collapse, the gas diffusion pattern is outlined with the Leak-gun tracer-gas detector. These two techniques provide a comprehensive method for predicting the relative probability of roof collapse in operating coal mines.