Research on Resistance Verification and Instability Criterion of Flexible Formwork Concrete Wall Support for Leaving Tunnels Along the Gob

The stability of the overburden rock caving structure and concrete wall in gob-side entry retaining using a flexible formwork concrete wall is crucial for its success. This study focuses on the 52606 flexible formwork concrete wall in the Daliuta Coal Mine. By combining physical simulation and theoretical analysis, we examined the caving structure of overburden rock during the mining process and calculated the stability of the surrounding rock in the retaining roadway. The support resistance of the concrete wall in different stages determines its safety factor. Results from the simulation experiment reveal that after mining the two working faces, the collapse of the overlying strata above the concrete wall forms a short cantilever beam structure, with a larger collapse angle on the concrete wall side compared to the coal wall side. The first fracture position of the roadway roof along the goaf is on the side of the concrete wall above the goaf, while the second fracture position is in the upper overburden rock forming the cantilever beam structure. The mechanical parameters needed to calculate the concrete wall's support resistance were obtained. The stability of the concrete wall during different mining stages is related to the ratio N of the ultimate load to the actual load. When N > 1, the concrete wall remains stable during the mining process. This study provides a significant theoretical basis for determining instability and controlling the roof in gob-side entry retaining with a flexible formwork concrete wall in China.