ABSTRACT:

The National Institute for Occupational Safety and Health (NIOSH) is conducting a monitoring program at the Pleasant Gap underground limestone mine in central Pennsylvania. This dipping mine is experiencing high horizontal stresses and is at a depth of over 400 m in the monitoring area. Part of this program includes using LiDAR measurements to assess the geotechnical condition of the rock mass and track movements of ground throughout the development of an instrumented pillar. A total of 79 LiDAR scans were collected from May 2017 through December 2018 that map the area surrounding an active development. The scans are particularly useful for establishing opening dimensions, mapping joint sets, and determining bedding spacing from breaks in the roof beam. Progressive damage has been shown on the ribs along the tall side of headings and on highly stressed pillar corners nearby active mining. Cutter roof formation is also prevalent in the monitored area, and the location and severity of this damage can be easily tracked. Most damage to the roof was observed after failure had occurred, but at two locations convergence was detected that has not yet resulted in failure. Convergence of the roof in excess of 5 cm is present in two intersections, one of which was also measured with a Miner's Helper, and appears to be correlated with adjacent development. The scanning program able to consistently and effectively track and measure a variety of displacements related to high stress and stress reorientation.

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