Rational width of narrow coal pillar based on the fracture line location of key rock B in main roof

In this paper, to master the influence law of the main roof's fracture structure on the stability of narrow coal pillar, the mechanical model of surrounding rock structure in gob-side entry was built, three fracture forms of the overlying main roof in gob-side entry were put forward, and the correlation between the fracture structure of main roof and the stability of narrow coal pillar was analyzed. The results show that there are great differences in the stress of roadway surrounding rock, and the stress and strain in coal pillar while the fracture line of main roof locates in different places. When the fracture line of main roof locates just at the top of the roadway, the surrounding rock deformation closed to the goaf is larger than that closed to the entity coal wall. The stress in the roadway roof is reduced fast, the surrounding rock is crushed and its anchoring ability is pool. The stress and deformation in pillar are increased fast, and the loads on the pillar are the largest when the surrounding rock is stable. Meanwhile, the continuous deformation speed of coal pillar is also the largest, which leads to the difficult later maintenance of roadway. When the fracture line of main roof locates in the lateral of roadway, the pillar deformation is in a reasonable scope, and the supporting capacity is strong, which is beneficial to the maintenance of roadway. The research results have been applied successfully in the No. 8105 fully mechanized face with sub-level caving of Yanjiahe Coal Mine, and satisfactory technical and economic effects are achieved.