A mechanised extraction methodology by continuous miner technology is designed for a deep-seated coal seam under massive strata and high in-situ stress conditions by analyzing the stability of rock mass and the rock burst potential through numerical simulation and field investigation. The coal seam having a horizontal-to-vertical in-situ stress ratio of 2.31, is overlaid by the massive sandstone strata and dolerite sill. 3-D numerical simulation is performed to evaluate the stability of rock mass and accumulation of elastic and plastic energy vis-à-vis strain burst index during different stages of the extraction. The energy-based safety factor approach is applied to identify the failed rock mass in the working places to design the support systems to minimise the failure of surrounding rock mass and the rock burst phenomenon. This paper would help the researchers to extract the highly stressed coal seam under massive strata safely and efficiently.
The prime stability problems at the time of the exploitation of deep-seated coal reserves by underground mining are high in-situ stress conditions causing in bump/burst viz., strain bursts, pillar bursts, and fault slip bursts (Hedley 1992). When the direction of major principal in-situ stress is parallel to the bedding plane, the likelihood of strain burst in the bedded deposits of coal measure sedimentary rocks increases. It causes shearing among the bedded strata (Wang et al. 2016). The roof experiences shear and compressive stresses while the side wall experiences tensile stress in a roadway due to high horizontal stress. If the uncaved roof strata are more prevalent in the goaf/void during the extraction of the coal pillars, the strain burst further increases. It propagates high stress in the surrounding rock mass and the coal pillars at the abutment zone. With the enlargement of goaved-out areas, the critical limit of the stress state is exceeded in the hard roof, resulting in the caving of the hanging roof. The coal mine bump or burst is caused by the rapid release of energy stored in the coal pillars and the surrounding rock mass as a result of the separation and fall of huge overhanging hard strata. The portions of the overhanging roof further increase if the size of remnant/rib pillars is not optimum. The small-sized remnant pillars result in a violent and uncontrolled collapse of the surrounding rock mass whereas the large-sized remnant/rib pillars inhibit the caving of hard roof strata. Furthermore, the unrestrained caving of competent strata frequently goes to the abutment zone. Consequently, the adequate support system, as well as the optimum design of rib/remnant pillars reduces the occurrence of bump/burst and uninhibited roof collapse during the mining of the coal seam under competent and hard strata. This paper describes one such case study of Churcha mine (RO) of South Eastern Coalfield Limited (SECL), India where a suitable extraction methodology and support pattern are designed by field study and numerical simulation.
