Strata behaviour during depillaring in Blasting Gallery panel by field instrumentation and numerical study

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 geo-technical 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 geo-mining 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.