No abstract

No abstract

Selection of a suitable mining method for economical and safe underground extraction of a thick coal seam is an extremely delicate process and brings a number of geotechnical parameters into consideration. Charbonnage de France (CdF) proposed Blasting Gallery (BG) for the extraction of virgin thick seams as well as developed pillars in thick seams in a single lift. The method was very successful resulting in 85 % of extraction with high productivity. But this method experienced strata control problems during final extraction at East Katras Colliery in Jharia Coalfield, Coal India Ltd., and also at GDK No. 8 Incline, Singareni Collieries Company Ltd. In this paper, the role of different parameters influencing development of mining-induced vertical stress, and maximum roof deformation in a BG 1/12 panel (GDK No. 8 Incline, SCCL) during depillaring in specific geomining conditions was visualized through numerical simulation models using ANSYS software. In this study, extensive field monitoring is carried out using modern instruments such as vibrating wire stress gauges, extensometers, load cells, and telescopic convergence rods to understand the strata behaviour during depillaring in the BG panel. Salient findings of field instrumentation data analysis such as mining-induced vertical stress development over the pillars, load over the support, bed separation at different horizons, and convergence of roof in rooms with face advance are presented in this paper. The results of induced stress, deformation, and factor of safety of pillar obtained by the finite element method (FEM) analysis are validated with the results of field instrumentation data analysis.

Background: Selection of a suitable mining method for extraction of a thick coal seam with optimal recovery and safety is an extremely delicate process. In fact, single lift working of full thickness of a thick coal seam has always a verge over the multi-slice working due to favorable economics and high production and productivity. Blasting Gallery (BG) method is suitable for extraction of virgin thick seams as well as developed pillars in thick seams in single lift. The method was very successful resulting in 85% of extraction with high productivity. But, this method experienced strata control problems during final extraction. The presence of strong and massive overlying roof strata caused high values of the mining induced stress over the pillars facing the goaf line during the depillaring. High values of mining-induced stresses in and around a depillaring face of thick coal seam generally create a threat of pillar overriding.