A New Model for Calculating Voidage in Goaf Under Roof-Cutting Pressure Relief Mining: Exploring the Influence of Volumetric Strain on Voidage From the Perspective of Finite Element

Abstract

Roof cutting and pressure relief mining technology has been applied in coal mine enterprises because of its advantages of improving the resource utilization rate. Compared to the previous longwall mining mode, the roof unloading and caving characteristics of goaf have undergone significant changes, leading to different patterns of overlying rock fracture and permeability variation in the goaf. To clarify the flow field characteristics of the goaf under the R-CPR mining mode. Based on the theory of “conservation of mining space,” this paper constructs a voidage model of the goaf based on the theory of body strain and subsidence of the rock layer overlying the goaf, with the theory of body strain and the amount of subsidence as the entry point. The void fraction model of goaf based on volume strain theory is constructed, and the applicability of the model is verified. The results show that the body strain voidage model cut top side voidage is significantly smaller than the uncut top side voidage. The porosity of the top cut side of the bulk strain porosity model is significantly smaller than that of the uncut top side; the stable wind speed of the working face is 0.78 m/s, and the air leakage rate of the goaf is 50.93%. In similar simulation experiments, the wind speed of the working face was stable at 0.72 m/s, and the air leakage rate in the goaf was 49.2%. In the actual project, the test stable wind speed is 0.75 m/s, and the actual goaf air leakage rate of the project is 44.1%, and the overall error is not more than 5%. This study enriches the theory related to voidage in the goaf. It provides the theoretical basis and practical reference for the prevention of air leakage and gas management in the R-CPR mining goaf.