Overburden Failure Associated with Mining Coal Seams in Close Proximity in Ascending and Descending Sequences Under a Large Water Body

We investigated differences of overburden failure induced by mining multiple seams in ascending and descending sequences under a large water body. A case study that involves mining in an ascending sequence was the Beizao coal mine, which is under the Bohai Sea, and one that involves mining in a descending sequence was the Cuizhuang coal mine, which is under Weishan Lake. Using numerical simulations with the same geological conditions as the in-situ measurements, the effects of different interburden thicknesses on mining were compared. The results showed that the ratios of the heights of water-conducting fractured and caving zones to the cutting height both increased as the interburden thickness was reduced. An ascending sequence is recommended where there is a thin interburden and thin bedrock, and where the mining seams obviously interact. The descending sequence is recommended where there is no apparent interaction between the seams. Both will produce a relatively small water-conducting fractured zone.