Mechanism and Engineering Practice of Roof Stability for Secondary Gob-Side Entry Retaining in Deep Mines

In order to reuse the gob-side entry retaining and preserve it as a long-term return air channel, thereby alleviating the tense relationship between mining and excavation, and reducing roadway excavation costs, this paper proposes the secondary gob-side entry retaining technology. It elaborates on the movement law of the overlying strata throughout the entire process of secondary gob-side entry retaining, introduces the concept of “major and minor structures” for roof support, establishes a mechanical model of the roof structure for secondary gob-side entry retaining, derives the calculation formula for the roadside filling body, analyzes the main influencing factors conducive to the stability of the overlying strata structure for secondary gob-side entry retaining, and presents the “four-in-one” surrounding rock control technology for secondary gob-side entry retaining. The research results indicate that: (1) The “major structure” of the overlying strata for secondary gob-side entry retaining tends to stabilize only after being subjected to three mining disturbances. (2) The coordinated load-bearing of the “minor structure” in roof support is the key to surrounding rock stability. A “four-in-one” surrounding rock control method for secondary gob-side entry retaining is proposed, which integrates the roadside backfills on both sides, the roof bolt-cable support system, the floor, and the internal roadway support to form a stable load-bearing structure. (3) Properly reducing the roadway width, the widths of the two backfills, and the cantilever length of the main roof on the goaf side can enhance the support strength of the coal rib during the gob-side entry retaining stage. This, in turn, reduces the load on the two backfills in the secondary gob-side entry retaining stage, thereby alleviating surrounding rock pressure. The research findings have achieved favorable results when applied in engineering practice, demonstrating both theoretical value and practical significance for supporting roadways under similar conditions.