Character of water or barometric pressure jump within karst conduit in large strong drainage area of karst water filling mine in Dachengqiao, Ningxiang, Hunan

Meitanba Coal Mine, Hunan Province, is one of the coal mines famous for karst water flooding in China. Its current mining level is about -400 m and the quantity of pumped water from the mine is about 11 000 m3per hour. For long, due to the continuous mine water drainage a great groundwater depression cone with an area of 219.19 km2 has been formed. Generally, most sinkholes induced by the mine drainage mainly occur in three stages, which include drainage beginning, groundwater level dropping beneath the bedrock surface and the occurrence of water inrush incidents, so sinkholes would not be appeared in dewatering zone. But more and more sinkholes have formed in recent years, even though the authorities have taken a series of countermeasures to control these karst hazards. In order to analyze the mechanism of sinkhole formation and help the government make decision, the Dachengqiao region was selected as a pilot site to identify the dynamic source of sinkholes. Data derived from the monitoring of water or barometric pressure within karst conduit show that the fluctuation of barometric pressures in the dewatering zone is extremely significant with a maximum fluctuation range of 54.72 meters happens in a year and a maximum instant variation velocity of 70.6 cm/min, which is believed to the air blasting and soil collapsing triggered by the sinkhole collapses that create the abrupt jumps of the barometric pressure.