Mechanism and engineering practice of roof stability for secondary gob-side entry retaining in deep mines

To facilitate the reuse of the gob-side retained entry as a long-term return airway, alleviate mining-excavation pressure, and reduce roadway development costs, this paper proposes a secondary gob-side entry retaining technique. The study examines the movement behavior of overlying strata throughout the entire process of secondary gob-side entry retaining, introduces a roof support concept based on "major and minor structural zones," establishes a mechanical model of the roof structure for secondary retention, derives a design formula for the roadside backfill, analyzes the main factors influencing the stability of the overlying strata structure, and proposes an integrated "four-in-one" surrounding rock control technology for secondary gob-side entry retaining. The results indicate that: (1) The "major structural zone" of the overlying strata stabilizes only after experiencing three mining disturbances. (2) The coordinated load-bearing behavior of the "minor structural zone" in roof support is crucial to surrounding rock stability. A "four-in-one" control strategy is proposed, integrating the roadside packing bodies on both sides, the roof bolting-cable system, floor reinforcement, and internal roadway support to form a stable load-bearing structure. (3) Appropriately reducing the roadway width, the widths of the two packing bodies, and the cantilever length of the main roof on the goaf side can enhance the support capacity of the coal rib during the initial retention stage. This reduces the load on the packing bodies during the secondary gob-side entry retaining stage, thereby alleviating surrounding rock stress. The proposed approach has yielded favorable outcomes in engineering practice, demonstrating both theoretical relevance and practical significance for supporting roadways under similar conditions.