Experimental Research on Dynamic Evolution Characteristics of Roof Movement and Mining-Induced Stress of Superimposed Mining in a Close Distance Coal Seam Group

To obtain the evolution characteristics of roof movement and mining-induced stress, the evolution of roof movement and mining-induced stress are investigated during the mining of close coal seams based on 2# and 3 + 4# coal seams in Shaqu coal mine. The results show that characteristics of macro-migration for overlying strata by superimposed mining in close coal seams are similar to that in a single coal seam. Roof strata present coordinated migration of multiple strata, and the displacements increase progressively. Roof strata can alleviate ground pressure as a cushion due to 2# coal seam mining, which reflects the stress-weakening effect under superimposed mining in close coal seams. Compared with 2# coal seam mining, the interval, support load, and dynamic pressure coefficient are reduced during periodic weighting in the 3 + 4# coal seam, and some parts of the rock undergo step-like sink. Based on above results, the hydraulic supports with high-rated working resistance are selected for superimposed mining. Finally, there was no failure among hydraulic supports or other dynamic disasters because of auxiliary measures implemented, and intensive management attention, during periodic weighting.