Strength Characteristics of Highly Anisotropic Burst-Prone Coal Considering Mineralogical Compositions

This paper was developed as part of an effort by the National Institute for Occupational Safety and Health (NIOSH) to identify risk factors associated with bursts/bumps in the prevention of fatalities and accidents in highly stressed, burst- or bump-prone ground conditions. In this study, we evaluated the effects of different shapes and distribution densities of mineral grains in coal on failure mechanics using the numerical software 3DEC. The main aim of this study was to identify possible failure mechanisms influenced by mineral habit and frequency in coal. Exploring differences in failure mechanics associated with the mineral grains helped to determine the role of mineral character as a possible contributor to characterize burst-prone coals. To achieve the goal of this study, a series of numerical specimens were prepared in the 3DEC model as follows: first, the 3DEC modeling in conjunction with the DFNs (Discrete Fracture Networks) technique was performed to explicitly generate the discontinuities (i.e., cleats and bedding planes) in the numerical specimens based on the results of laboratory analyses. Then, the different realizations of mineral grains were embedded in the 3DEC model to simulate an unconfined compressive strength (UCS) test to assess the influence of the mineralogical characteristics on the UCS. The type of catastrophic failure in coal mines known as dynamic failure—also colloquially referred to as bumps, bounces, bursts, and others—is one of the most challenging and persistent engineering problems associated with coal mining in highly stressed conditions. Coal pillar bursts involve the sudden expulsion of coal and rock into the mine opening. These events occur when stresses in a coal pillar, left for support in underground workings, exceed the pillar's critical capacity, causing the pillar to rupture without warning. These events can be exceptionally violent, ejecting coal and rock with explosive force (Peng 2008; Kim and Larson 2017). Many uncertainties remain in the highly anisotropic characteristics of coal seams associated with geologic structure and spatial redistribution of induced stress in coal pillars due to mining activities (Kim et al. 2018; Kim and Larson 2021). Thus, to prevent fatalities, continuous effort is required to better understand this type of catastrophic failure mechanism in coal mines. This paper is developed as part of an effort by the National Institute for Occupational Safety and Health (NIOSH) to identify risk factors associated with bumps to prevent fatalities and accidents in highly stressed, bump-prone ground conditions.