Study on Roof-Control Technology for Gob-Side Entry Retaining Under Composite Roofs

Abstract

This paper addresses the challenge of roof control during gob-side entry retaining under a composite roof. Taking the 15210 working face of Hecaogou No. 1 Mine as the engineering background, borehole-camera exploration, numerical simulation, and field measurements are integrated to systematically investigate the mining-induced failure mechanism of roadway surrounding rock and the corresponding stability-control technology. Borehole observations reveal typical damage features of a composite roof, characterized by pervasive fractures and pronounced interlayer separation. FLAC^3D simulations clarify the spatiotemporal evolution of the surrounding-rock plastic zone with face advancement; the whole process is divided into four stages—stable excavation, presplitting-induced expansion, mining-induced expansion, and post-mining stabilization—and the corresponding spatial regions are identified. The results show that: (1) The spatiotemporal evolution law of the plastic zone from excavation to abandonment exhibits a “dynamic–static coupling” mechanism, where the dynamic failure process corresponds to the static damage state. This correspondence provides a key theoretical basis for interpreting roadway deformation mechanisms and designing stage-wise support schemes. (2) By analyzing the stress-field evolution under presplitting and mining disturbance, the mechanical mechanism of asymmetric plastic-zone propagation is revealed. The stress field around the retained entry presents an S-shaped three-zone distribution: mining-influence stable zone, mining-influence zone, and excavation-influence stable zone. This stress evolution is the fundamental reason for asymmetric plastic-zone expansion. (3) The propagation morphology is clarified: during presplitting and mining disturbance, the depth and extent of the plastic zone increase markedly, and roof development is far greater than floor development. Damage and deformation concentrate around the presplitting boreholes and in the roof region extending from the boreholes toward the working face. (4) Based on the above spatiotemporal laws, a targeted reinforcement-support method is proposed. Guided by plastic-zone morphology and field monitoring, the method accurately determines reinforcement locations and parameters, effectively stabilizing surrounding rock and ensuring safe longwall production.