PURPOSE:  This project serves to design, test, and demonstrate the potential of monitoring technologies to warn of roof fall occurrences.

RESEARCH SUMMARY:  Reducing the number of ground fall injuries is a central goal of the NIOSH mine safety research program. This research effort is aimed at advancing our basic understanding of the causes of ground falls and using this knowledge, in conjunction with state-of-the-art monitoring technology, to warn of large roof fall occurrences. Central to this project will be the collection of microseismic and roof deflection information from several sophisticated monitoring systems at field sites where roof falls occur. These monitoring data will be compared with actual field observations to determine: the characteristics of the detectable roof falls; the timing sequence between roof falls and measurable microseismic activity; trends in the data to warn of roof falls; and limitations in this technology to anticipate roof falls.

The ability to determine the location and timing of roof falls has been a long standing goal of safety professionals. The combination of microseismic monitoring and roof deflection measurements produces complementary information that more completely characterizes the pre-fall behavior of roof rock strata. This enhanced technology provides the kind of information needed by on-site personnel responsible for worker safety, to anticipate the occurrence of hazardous roof falls.

NIOSH is in the process of deploying several monitoring systems at mines with known roof fall problems so that an extensive database of microseismic emissions and roof-to-floor convergence and roof beam sag measurements can be established. These sites are from mines with varying geologies, stress conditions, and mining methods. It is recognized that several years will be needed to collect enough data to adequately prove or disprove the viability of this technology. In 2001-2003, several roof falls were monitored at an underground stone mine in southwestern Pennsylvania. In 2004, the microseismic database from the Moonee Colliery longwall coal mine in Australia was obtained and event trends were compared with roof fall occurrences. In early 2005, a South African microseismic monitoring system was deployed at an underground stone mine in northern West Virginia. In late 2005, a Canadian microseismic monitoring system is scheduled to be deployed in a deep, steeply dipping stone mine in central Pennsylvania. In each case, monitoring will continue for 6 to 12 months and information on the geology, stress field, and mining methods will be collected. Additional field sites will be added in the future to continue to broaden NIOSH’s database.