Study on Pressure Characteristics and Roof Subsidence Law of Narrow Strip Filling Mining

Aiming at the problem of difficult mining of coal resources under buildings, railroads and water bodies in northern Shaanxi, China, a narrow strip filling mining (NSFM) method is proposed. The four-wheel cyclic mining and filling technology is systematically introduced, the method of theoretical analysis, numerical simulation and physical similarity simulation experiment is adopted to carry out the research, and the pressure rule of filling body—coal pillar and the control effect of roof in the mining and filling process are clarified. The finite beam model of elastic foundation is established, the discriminative basis of roof instability is put forward, and the key parameters of filling mining are deduced. The numerical simulation results show that in the process of four-wheel cyclic mining and filling, the backfill filled in this stage starts to participate in the load bearing after the next stage of coal pillar is mined, and the backfill regularly shares the overburden load in stages. The overall subsidence pattern of the immediate roof is similar to that of the "square basin", and the final subsidence of the immediate roof is 0.08 m, which is at a relatively low level. The physical similarity simulation experiment verifies the above conclusion, no separation layer and cracks appear in the roof of coal seam, and the filling body and coal pillar maintain stable safe bearing state. This method can improve the recovery rate of coal resources, control the roof subsidence in a small range, and provide a feasible solution for sustainable mining of coal seam under buildings, railroads and water bodies.