Study on the overburden failure law in thin coal seam mining without coal pillars under complex geological conditions

To improve the recovery rate of thin coal seams under complex geological conditions and to investigate overburden failure and migration during pillarless mining, a study was conducted at a fully mechanized coal mining face in the Yuwang Coal Mine. Based on key strata theory and the “110” mining method, the research integrated theoretical analysis, physical similarity experiments, and numerical simulations. Strain and infrared monitoring systems were used to observe the deformation characteristics of the overlying and surrounding rocks in the roadways during roof cutting and pressure relief. Monitoring focused on two aspects: the displacement field and the temperature field. The study optimized roof cutting parameters for thin coal seam working faces in complex geological settings and proposed a surrounding rock control technique for gob-side entry retention, based on mine pressure monitoring data. Results indicate that the roof cutting angle significantly affects roof movement. Optimal conditions for minimal roof displacement and subsidence were observed at a cutting angle of 75°and an average cutting height of 7 m. Asymmetric movement of the overburden was observed on both sides of the cutting seam, with a short-arm beam structure forming upon roof cutting, which helped slow the overburden movement. Preferential collapse occurred on the cutting seam side, resulting in greater subsidence displacement compared to the non-cutting side, thereby relieving roof pressure. The implementation of the “cutting roof pressure relief NPR cable stress compensation” technique effectively addresses the stability issues of surrounding rock in pillarless mining by mitigating roof pressure through controlled roof cutting.