New Karst Sinkhole Formation Mechanism Discovered in a Mine Dewatering Area in Hunan, China

摘要

The Meitanba Coal Mine in Hunan province, China, has experienced severe karst sinkhole hazards since 1982. Mine dewatering that began in 1955 has produced a groundwater cone of depression encompassing an area of 219.19 km(2) as of 2014. Most dewatering-induced sinkholes occurred on three occasions: at the beginning of dewatering, at times when groundwater level dropped beneath the bedrock surface, and at times when water inrushes occurred. Sinkholes would not be typically anticipated in the stabilized groundwater cone of depression. However, over the last decades, many sinkholes including a large one, 80 m in diameter and 30 m in depth, that occurred at a primary school in 2010 have formed in the dewatering zone, even though a series of treatments have been taken to prevent such karst hazards. To determine the dynamic mechanisms of the sinkhole formation in the dewatering zone, the Dachengqiao region was selected as a study site and high-frequency monitoring of groundwater-air pressures was performed in the underlying karst conduit system. The monitoring results showed very intense pressure changes in the dewatering zone with a maximum fluctuation of 54.72 m and a maximum instant fluctuation rate of 70.6 cm H2O/min. The abrupt pressure changes are more likely caused by air blasting and soil collapse and can be a key factor triggering the sinkhole collapses.