ABSTRACT:

Over the past decade, rib failures have resulted in 17 fatalities, representing 52% of the ground-fall fatalities in underground coal mines in the United States. In an attempt to control rib failures in underground coal mines, researchers at the National Institute for Occupational Safety and Health (NIOSH) developed a coal-mass model that is capable of capturing the effect of face cleat and the development of rib fracturing. This paper presents research that is part of a continued effort to calibrate the coal-mass model using monitoring data collected at field sites. This paper presents the results of a field study in a longwall mine operating in the Lower Kittanning coalbed in West Virginia. The deformation of the roof and an instrumented coal pillar were monitored using multipoint extensometers, and stress changes at different depths in the instrumented pillar were monitored via borehole pressure cells (BPCs). The monitoring results in conjunction with visual observations were used to calibrate the controlling parameters of the coal-mass model. These parameters are: (1) a dimensionless parameter called “coal-mass scale” (CMS) which varies from 1 to 100. Small values of CMS represent a small-size coal specimen of high strength, and large CMS values represent a large-size coal specimen of lower strength, and (2) critical plastic shear and tensile strains that control rib fracture. The actual behavior of the coal-mass response and the stress transfer were replicated at three different stages of longwall retreat mining. This work provides a basis for continued research aimed at an engineering-based design of coal pillar rib support design.

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