Abstract:

Under the influence of the super-thick nappe overlying the coal seam, the fracture morphology of the overburden and the stress distribution change significantly after the extraction of the working face. The abnormal concentration of stress leads to large deformations in the roadway and increases the risk of roof collapse, thereby restricting the safe extraction of the working face. This paper takes the mining of 360801 working face under Fufeng super-thick nappe in Xinji No.1 Coal Mine as the engineering background. Firstly, similar material tests were conducted to investigate the structural evolution of the overlying strata under the influence of the super-thick nappe. It was found that after mining, the super-thick nappe above the working face bent and subsided as a plate-like structure. Meanwhile, the underlying strata developed an arching effect, forming an asymmetric pressure arch. Then, numerical simulation was used to analyze the stress distribution in the surrounding rock of the working face under the influence of the super-thick nappe. The simulations indicated that the asymmetric pressure arch in the overlying strata led to a markedly asymmetric stress distribution in the working face. The peak stress zone continuously shifted towards the front of the roadway, and the stress concentration increased as the face advanced. Compared with the non-nappe condition, the maximum displacements of the two sides and of the roof and floor in the roadway-intensive area increased by 32% and 52%, respectively. In addition, the peak stress increased by 8.86 MPa, and its influence distance ahead of the working face increased by 80 m. Finally, a mechanical model of the roof asymmetric pressure arch under the super-thick nappe was established, and the trajectory equation of the arch was derived. The influence range of the pressure arch was obtained, showing that with the increase of lateral horizontal stress, coal seam thickness, and burial depth, the range of pressure arch influence gradually expands. Furthermore, the reasonable stop-line for mining was determined to be 240 m from the roadway dense area. Field measurements showed that the maximum loads on the anchor cables and bolts supporting the surrounding rock in the roadway-intensive area were 176 kN and 38 kN, respectively. The maximum convergences of the roof-to-floor and side-to-side were 198 mm and 118 mm, respectively, representing reductions of 43.4% and 26.9% compared with those observed during final mining of the adjacent 360803 working face. The stability of the surrounding rock was significantly improved. The study provides a theoretical basis for designing stop-line positions and controlling surrounding rock in working faces under similar geological conditions.

Key words: super-thick nappe, overburden structure, asymmetric, pressure arch, stop line