A sustained failure mitigation method for roadways in coal pillar recovery working faces of deep mines: excavated pressure-relieving roadways and combined support technology

Roadways in deep mining are strongly affected by high in-situ stress and mining-induced stress, exhibiting characteristics of sustained large deformation failure in surrounding rock control. Mere strengthening support is insufficient to prevent the persistence of such failure. In this case, sustained rib extrusion occurred in the deep mine coal pillar recovery working face (CPRWF), leading to frequent failure of the anchored body, which remained uncontrollable even after repair support. Through geological investigation, on-site survey, and mechanism analysis, it was clarified that the superimposed stress borne by the 12.5 m-coal pillar is the root cause of inducing sustained deformation of the surrounding rock. Moreover, since the compression degree on the goaf-side of the coal pillar is significantly higher than that on the roadway-side, stress is transmitted to the coal pillar rib of the roadway, resulting in sustained coal extrusion. Based on this, a control concept of “stress source control - transmission path blocking - working environment improvement” was proposed. A pressure-relieving roadway was constructed in the 12.5 m-coal pillar, converting an entire section of wide pillar into two sections of narrow pillars, thereby directly improving the stress environment from the source and blocking stress transmission in the path. Furthermore, numerical simulation verified the effect of the pressure-relieving roadway, indicating that its optimal layout configuration is in the middle of the coal pillar, with an optimal cross-sectional size of approximately 4.0 m. Consequently, a comprehensive technical scheme was established, including advanced roadway excavation for pressure relief, double-roadway combined support, and full recovery of coal pillars. This scheme not only achieved control over sustained deformation failure but also recovered an additional 7,657 tons of coal pillar resources. Meanwhile, the double-roadway combined support method successfully prevented and controlled the sustained failure of surrounding rock. This study provides an innovative solution for blocking sustained failure through deep stress regulation by establishing pressure-relieving roadways, offering technical references for the safe and efficient recovery of deep resources. This paper investigates the occurrence mechanism and control method of sustained large deformation failure in the surrounding rock of the air-intake roadway in deep CPRWF. Through geological investigation, on-site survey, mechanism analysis, simulation verification, and engineering practice, a control concept of “stress source control - transmission path blocking - working environment improvement” for sustained failure is proposed and successfully applied, the highlights of this research in the field of engineering failure are: • It is found that the compression degree on the side of the coal pillar is significantly higher than that on the roadway side, and stress is transmitted to the coal pillar rib of the roadway, resulting in sustained coal extrusion. • Aiming at the continuous deformation of coal pillar side, the failure control idea of “stress source control-transmission path blocking-action environment improvement” is proposed. • Numerical simulation verified the effect of the pressure relief roadway, indicating that its optimal layout configuration is in the middle of the coal pillar, with an optimal cross-sectional size of approximately 4.0 m. • A comprehensive technical scheme involving advanced roadway excavation for pressure relief, double-roadway combined support, and full recovery of coal pillars has been established and successfully applied.