ABSTRACT

: The National Institute for Occupational Safety and Health (NIOSH) is investigating the unique pillar stability issues associated with room-and-pillar mining in dipping underground stone mines. A seismic and stress monitoring system has been installed at a dipping underground stone mine in central Pennsylvania. This monitoring system consists of 18 uniaxial accelerometers and 3 vibrating wire biaxial stressmeters. These sensors were installed in the roof nearby a future pillar as well as into the exposed rib of the future pillar to capture the development loading as the remaining three sides are excavated. Synchronized seismic and stress data have been collected for a period of four months, with the most recent eight weeks of data containing the response to nearby development. Following blasts, 2,336 microseismic events were located nearby the instrumented pillar, and passive seismic activity that does not correspond to blasting or equipment operations was also located near the pillar. Very little stress change has occurred during the monitoring period due to the early stages of adjacent mining, but nearby blasting does show distinct stress changes. The events that have occurred in the instrumented future pillar average a higher energy than those on the excavation perimeter. Monitoring will continue through the complete development of the pillar, which is expected to require an additional 6-12 months.

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