文摘
Voids in overburden disturbed by coal mining provide channels for transfer of heat, methane, groundwater, oxygen, exhaust gas and fire-fighting materials in the underground environment. Based on expressions of strata and ground subsidence, a group of void fraction distribution models are proposed, including porosity in the caved zone, the fracture ratio in the bed separation zone and the fissure ratio in the ground subsidence zone. Combined with a case study of the Antaibao coal mine, China, theoretical calculation and numerical simulation indicate that porosity distribution in the caved zone is U-type and the transverse void fractions in the bed separation zone and ground subsidence zone have M-type distributions. Additionally, the longitudinal void fraction distribution changes from ∩-type to M-type along the strike and dip of the coalbed after the complete subsidence of ground. The distribution of fractures in the disturbed overburden of the goaf presents a “fractured arch”, and fracture density gradually decreases from arch foot to crown. Fire-prone zones, propagating paths of coalbed fires, areas prone to water influx and outlets of boreholes used for fire-fighting all usually appear around the perimeter of disturbed overburden. The transverse void fractions distribution in the bed separation zone changes from ∩-type to M-type with an increase in the size of the goaf. It is suggested that the inlets of gob vent boreholes should be arranged near the center of the bed separation zone in the early stages of longwall mining, and around the perimeter in middle to late stages of mining. Keywords Coal Longwall mining Disturbed overburden Mining-induced voids Void fraction Anisotropy