Research on the Instability Mechanism and Filling Surrounding Rock Control Technology of Fully Mechanized Top-Coal Caving Face Passing Through Abandoned Roadways

Abstract

When a fully mechanized top-coal caving face passes through abandoned roadways, accidents such as shield support failure and roof collapse are likely to occur. To address this issue, this study focuses on the 3107 fully mechanized top-coal caving face at Huanglian Coal Mine of the Huangcheng Xiangfu Group in Yangcheng, Shanxi Province, as its engineering context. Using a combination of theoretical analysis, numerical simulation, and field experiments, it systematically investigates the fracture behavior of the main roof and how the surrounding rock of the abandoned roadway is controlled during this process. First, the evolution of stress in the gradually changing coal pillar during face advance and the instability process of the abandoned roadway were analyzed, along with the impact on mine pressure when the main roof fractures above the coal pillar, the abandoned roadway, and the solid coal mass, respectively. A mechanical model of a cantilever beam was established based on the Winkler elastic foundation beam theory, deriving the bending moment equation for the main roof. The research shows that the wider the abandoned roadway, the greater the bending moment in the main roof, and the higher the risk of fracture and instability. Furthermore, a mechanical model of the fractured main roof was created based on the voussoir beam theory, which determines that the minimum support strength needed to prevent sliding instability of the main roof is 3.5 MPa. FLAC3D was used to simulate and compare the surrounding rock stress and plastic zone distribution of the abandoned roadway under different filling body strengths. The simulation results indicate that a filling body strength of 3.5 MPa (corresponding to a water–cement ratio of 3:1) is appropriate. A segmented isolation and compact filling method for the abandoned roadway was proposed and applied in engineering practice. Monitoring results showed that during the face advance through the abandoned roadway, the roof of the roadway remained stable, the hydraulic support pressure at the working face stayed within a safe range, and no accidents such as support failure or roof collapse occurred. The filling support technology using high-water-content, quick-setting materials proved highly effective, ensuring the successful passage of the fully mechanized top-coal caving face through the abandoned roadway.