Fracture evolution of the main roof in gob-side entry retaining by roof cutting of an inclined coal seam

Abstract

During the application of gob-side entry retaining by roof cutting in inclined coal seams, the boundary conditions of the main roof in the goaf will change, resulting in the special characteristics of its fracture evolution. This article established a main roof elastic mechanics model through theoretical analysis and obtained the stress expression of any point on the main roof, analyzed the stress distribution characteristics and fracture evolution law of the main roof, finally, and revealed the unloading mechanism of the overburden in the cutting roof of goaf by combining with field mining pressure data. The results show that the stress value on the main roof is related to the dip angle, the poison's ratio, and the geometry parameters of the working face. The main roof stress presented an asymmetric distribution in the inclined direction. The fracture mode of the main roof is the “U-Y” mode under the first weighting and the “L-Y” mode under periodic breakage. The pressure on the upper part of the working face increased, while the lower part decreased according to field mining pressure data. There are two reasons for the reduction of pressure in the lower part of the working face, on the one hand, the reduction of the area of the key block A leads to a decrease in load, on the other hand, the gangue filling and supporting effect of the lower part of the goaf. The surrounding rock of the gob-side entry is not obviously affected by the dynamic pressure, and the deformation is small, achieving a good retaining effect.