Four people have now been confirmed dead at a coal mine in Shandong Province, China, following a roof collapse on Saturday 22 February 2020. The incident happened at the Longgu Coal Mine in Juye County, slightly after 6.15 am local time, and has been described by local media sources as a 'coal bump'; an incident in which a supporting column left behind as a seem of coal is excavated suddenly gives way, bringing down the roof of the tunnel.
The approximate location of the Longgu Coal Mine. Google Maps.
Coal bumps are a common problem during 'room and pillar' mining, a system in which a horizontal bed of the target mineral (usually coal) is removed by the excavation of a series of tunnels arranged like streets on a city block, leaving behind blocks of unmined material to support the ceiling of the tunnels. During coal bumps one or more of these blocks fails abruptly, and often explosively, due to pressure caused by the weight of material above overwhelming the structural integrity of the block. The amount of pressure such a block can withstand relies a great deal on the local geology, but the method becomes less safe at greater depths, and in the US is generally considered risky at depths of greater than about 150 m.
The coal seem targeted by the Longgu Coal Mine is much deeper than this, with a buried depth of 778.6-848.6 m and an average depth of 813.6 m. In a paper published in the journal Energy Science & Engineering on 17 September 2019, a team of scientists led by Yunliang Tan of the State Key Laboratory of Mining Disaster Prevention and Control at Shandong University of Science and Technology, report seeing pressure deformation within the Longgu Coal Mine, and showed that the maximum vertical stress, deformation, and failure range of the surrounding rock for super‐large section chambers of the type being used at Longgu are larger than those of an ordinary section chamber, and make a number of suggestions for modifying the design of future excavations.
Signs of deformation within the Longgu Coal Mine. Tan et al. (2019).
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