Stability assessment of heightened rib/snook during extraction of a thick coal seam by continuous miner in single lift

Continuous miner (CM) of 4.6 m working height is adopted to extract 6.0 m thick coal seam in single lift at GDK 11 Incline mine. Nine panels of this mine with their depth variation between 150 and 310 m have been satisfactorily depillared using CM. Field observations found that the different sizes (w e /h = 0.92–2.23) of remnants (ribs/snooks) of pillar were intact even when their position is shifted in goaf during 4.6 m extraction height in the initial two panels with average depth variation between 277 and 295 m. It provided an opportunity to further extract the 2 m thick floor coal bottom which were left-out inside the goaf during extraction in the previous two panels. Numerical modelling studies for assessing the competency of 6.0 m heightened remnants supported extraction of full thickness of the seam in single lift. These were further verified with the observations of strata monitoring during extraction of 6.0 m thick coal seam using the same CM of 4.6 m cutting height. Extraction of thick coal seam up to 6.0 m in subsequent panels of the seam experienced safety factor of heightened snook (w e /h = 0.69–1.52) ranging from 0.27 to 0.47 between 160 and 254 m depth of cover. Discussing site conditions of the mine, this paper presents design of rib/snook for safe and efficient extraction of a thick coal seam in single lift. Article highlights Manner of pillar extraction was modified after extensive field and numerical modelling investigations to extract total thickness (6.0m) of thick coal seam in single lift. Competency of heightened rib/snook up to 6.0m was found to be satisfactorily during the mechanized depillaring using 4.6 m cutting height of the continuous miner. Seven panels of the mine are extracted satisfactorily with increase in production, productivity and safety along with conservation of more than 1.19 Mt bottom coal.