Longwall mining under massive conglomerate roof: Case studies of Australian underground coal mines

Massive conglomerate roof in close proximity to coal seams is a dominant feature in Newcastle Coalfield. Longwall mining under such roof strata results in 'hang up' which can collapse suddenly and often without warning, giving rise to a phenomenon known as 'wind blast'. Field studies and laboratory investigations have revealed some aspects of the dynamics of the interaction between falling roof elements and the air below. The permeability of the roof elements and bed separation prior to fall, play a significant role. Field investigations have correlated wind blast intensity with roof fall areas and its attenuation with distance. The ongoing investigation will help in site characterisation with respect to wind blast risk assessment under various roof overhang conditions and establishing norms for safe design and layout of longwall panels under massive roof condition.