Study on disaster mechanism of thick and hard overhanging roof and top cutting control technology

To address the challenges of significant deformation and high instability risks in the surrounding rock of unsupported roadways beneath a laterally thick and hard overhanging roof, this study focused on the 3810 working face transport roadway in Majiliang mine, Datong coalfield. A mechanical model of the laterally thick and hard overhanging roof was established, determining the theoretical values for the optimal top cutting position to be 3.98 m from the side of the external faulted coal pillar goaf. A UDEC numerical simulation model was developed to analyze the effects of roof length and fracture position on the stress distribution in the coal pillar and the deformation of the surrounding rock in the roadway. The findings revealed that reducing the overhanging roof length and fracturing at a reasonable position above the coal pillar effectively decreased the lateral stress concentration in the coal pillar, minimized surrounding rock failure, and reduced roadway deformation. Based on these results, a top cutting and pressure relief control strategy was proposed, targeting the thick and hard overhanging roof on the coal pillar's goaf side. This approach promoted timely collapse of the roof, increased the height of the roof fall zone, reduced the load on the coal pillar, and provided lateral confinement, thereby enhancing the bearing capacity of the coal pillar. A hydraulic fracturing-based top cutting and pressure relief plan was proposed and implemented in field practice. Post-application results indicated that the surrounding rock deformation of the 3810 transport roadway improved significantly. After top cutting, the maximum convergence of the roadway sides was reduced to 600 mm, and the maximum roof subsidence was 277 mm. Compared to sections without the top cutting measure, roadway deformation decreased by 39.6% (sides) and 31.8% (roof). The effective cross-sectional area of the roadway met the requirements for safe and efficient mining operations.