Rib-failure related accidents in underground coal mines continue to cause injuries and fatalities. Investigation of the coal-mass failure process through numerical simulation is one approach to mitigate rib failures.

The paper presents a framework to describe the strength and deformation of a coal-mass. The peak strength is evaluated by the Hoek-Brown failure criterion. The residual stiffness and strength are evaluated by the Fang and Harrison degradation model. The dilation is defined by the Alejano and Alonso peak-dilation model.

Using laboratory and in-situ coal numerical models, regression equations were developed to scale-down the strength and degradation parameters of coal material. Through a try-and-error process, the appropriate parameters of coal-mass could be defined by matching the behavior of modeled rib to field observations. If such observations are not available, preliminary parameters of coal-mass are calculated for a specimen size of 1.5 m. Young’s modulus and Poisson’s ratio are 3.0 GPa and 0.25, respectively. The Hoek-Brown peak strength parameters "m", "s," and "a" of the coal-mass are 1.659, 0.015, and 0.5, respectively. The unconfined peak and residual strengths of the coal-mass are 4.3 and 0.35 MPa, respectively. The degradation parameter and the critical plastic shear strain of coal-mass are 0.485 and 0.2, respectively.


Potential rib instabilities, such as brow formation, toppling, bumps, etc. are threats in underground coal mines. Efforts to improve the stability of underground mine ribs have continued for decades. Despite the ongoing rib-support-related research, there has been a continual occurrence of rib-related fatalities in underground coal mines. While these efforts have contributed to the overall improvement in rib safety, the average fatality rate is still 1.3 fatalities per year over the last 18 years [1]. Because of the wide variation in requirements and design criteria nor a universal methodology for rib support, the National Institute for Occupational Safety and Health (NIOSH) is conducting research towards developing guidelines for determining the appropriate level of support and design methods for support systems to minimize the risk and severity of injuries to miners from rib falls in underground coal mines.

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