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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. [ABSTRACT FROM AUTHOR]

Filling mining is an important direction in green coal mining. In the filling site, a layered filling body can be formed due to technological problems. In this paper, we take Shanghe Coal Mine (Shaanxi Province, China) as the background. In order to explore the mechanical properties and failure modes of layered backfill, specimens with different layered proportions (1:1, 1:3, 3:1) were made and studied concerning the aspects of wave velocity, porosity, strength and failure modes. The experimental result demonstrates that with the increase of curing time and fly ash (FA) content, the porosity of ASPLB decreases, the wave velocity and the strength increases. In addition, the layered structure has a significant effect on the strength and failure mode of the specimen. Uniaxial compression experiments showed that after 28 days of curing with Ratio III, the strength of layered backfill (LB) was reduced by 14% and the strength of 3:1 LB was increased by 16.7% and 40% compared with 1:1 LB and 1:3 LB, respectively. A digital speckle experiment showed that the failure mode of ASPLB is a vertical fracture without penetration, and the fracture propagation of layered ASPLB is hindered by the stratification. Based on the above research, the scheme that meets the requirements of the Shanghe Coal Mine is determined, and its reliability is verified, providing guidance for scientific stratification and the filling of gob. [ABSTRACT FROM AUTHOR]

During strip backfilling mining in coal mines, the backfilling material is the main support structure. Therefore, studying the pressure law of the backfilling material is essential for the safe and efficient mining of coal resources. Based on research into strip backfilling mining at working face number 3216 of the Shanghe Coal Mine, and to smooth transition of overlying strata loads to the backfilling material, this study proposes a three-stage strip backfilling mining method. Based on thin-plate theory, an elastic thin-plate model, a reasonable spacing of strip mining is constructed, and the reasonable mining parameters of "mining 7 m to retain 8 m" at working face number 3216 of the Shanghe Coal Mine are determined. The law of backfilling pressure in three-stage strip backfilling mining is studied through numerical simulation and physical simulation experiments. The results show that field measurement results are basically consistent with the experimental results and numerical simulation results. When three-stage strip backfilling mining is adopted, the stage-one backfilling material is the main bearing body to which the overlying rock load transfers smoothly and gradually, and the structure of the "overburden-coal pillar (or backfilling strip)" in the stope remains stable. In three-stage strip backfilling mining, the overlying rock load is ultimately transferred to the stage-one backfilling material, the stage-two backfilling material is the auxiliary bearing body, and the stage-three backfilling material mainly provides long-term stable lateral support for the stage-one backfilling material. [ABSTRACT FROM AUTHOR]