Design of Key Parameters for Strip–Filling Structures Using Cemented Gangue in Goaf—A Case Study

Large–scale underground coal mining is bound to cause serious surface subsidence problems. However, conventional filling and mining methods have problems such as high cost and process difficulty. In order to achieve the purpose of high efficiency and low cost, this paper proposes using the technology of CGSG. To achieve the effective control of overburden strata movement and ground surface settlement using cemented gangue strip filling in the goaf (CGSG), this paper studies the design principles and methods of the key parameters of the strip–filling structure including the strength, compressed deformation characteristics, and sizes. Based on the analysis of the structures and movement characteristics of the overburden strata above the coal seam, the mechanical relationship between the strip–filling structure and the overburden strata was established. Formulas for calculating the parameters of the strip–filling structure were derived. Guided by the obtained index parameters, the material ratios and mechanical experiments of the filling body were designed. The research results demonstrated that the strengths of the cemented gangue filling body at different ages should be greater than the compressive load of the strata roof movement on the filling body during the same period; under the compression of the maximum load, the ultimate compressive deformation of the filling body should be less than the ultimate subsidence deflection of the basic roof strata. The width of the strip–filling structure was inversely proportional to its ultimate strength, while the width of the non–filling area was greatly affected by the length of the rock beam formed after the basic roof strata fractured. The research results were applied in the No. 7402 experimental strip–filling workface in Zhaizhen coal mine, China. Reasonable parameters of the cemented gangue strip–filling structure were designed. The field application results demonstrated that, after using the technology of CGSG, there was no obvious pressure appearance when the working face was mined. The maximum sinking value of the ground surface was only 30 mm after the mining of the working face was completed; at the same time, the filling cost was about one–third less than the complete–filling technology in the goaf.