Failure Characteristics and Evolution Law of Overburden Structure Under Repeated Mining of Close‐Distance Coal Seam Group in Ningdong Mining Area

ABSTRACT It is difficult to control the mine pressure in the coal face under the close coal seam group. On the basis of the mining background of 4‐1#, 4‐2#, and 4‐3# coal seams in the I01 mining area of the Ningdong mining area, the fracture characteristics and evolution law of the overburden structure under the close coal group are studied. The results show that after the mining of the 4‐2# coal seam, the subsidence of the overlying rock of the 4‐1# coal seam roof increased by about 0.98–1.34 cm. After the mining of the 4‐3# coal seam, it increased by about 0.87–0.97 cm. The subsidence of the roof is reduced by about 11.22% to 27.61%. When the 4‐1# and 4‐2# coal seams are mined, the overburden rock morphology of the stope presents a “trapezium” structure. When the 4‐3# coal seam is mined, the overburden rock morphology of the stope presents a “double trapezoidal” shape form. If the coal seam spacing is small, the roof overburden structure is simplified into a cantilever beam structure. If the spacing is large, the roof overburden structure will form the transfer rock beam structure. Through theoretical analysis, the calculation formula for the overburden failure height and the roof support strength is obtained. The error between the theoretical calculation results and the similar simulation results and the field measurement results is small, which is 4.1%–4.5% and 2.7%, respectively. The reliability of the theoretical calculation results is proven.