Abstract:
Addressing the significant challenge of surrounding rock control in deep gob−side entries within composite roof strata, where conventional pressure relief methods like hydraulic fracturing frequently encounter limitations including the difficulty in pinpointing the dominant controlling stratum and insufficient pressure relief scope, this study aimed to develop a targeted and effective technical solution by first deciphering the underlying mechanical behavior and subsequently applying a novel pre−fracturing approach; taking a typical deep gob−side entry in the Ningdong mining area as the engineering prototype, a mechanical model for stress transfer was established through theoretical analysis, and the dynamic coupling process between the lateral abutment pressure from the goaf and the front abutment pressure from the advancing working face was meticulously reconstructed using numerical simulation techniques, which collectively revealed the distinct mechanical characteristics of the entry under the superimposed influence of these multi−source mining−induced stresses; based on this foundational understanding, an innovative deep−hole presplit blasting technology designed specifically for roof cutting and pressure relief under deep composite roof conditions was proposed and implemented in the field, with its success critically dependent on the accurate positioning of the key stratum, which guided the determination of precise blasting parameters including a borehole depth of 60 meters and a charge weight of 75 kilograms per hole; comprehensive field monitoring now demonstrates that this technique, by effectively fracturing the identified key hard stratum, successfully blocks the stress transfer path within the suspended roof structure, resulting in a 33% reduction in the spatial range of the peak front abutment stress zone, and concurrently, it significantly lowers the energy accumulation level in the surrounding rock system, evidenced by a decrease of over 50% in both total microseismic energy and event frequency, alongside a 26% reduction in the energy release intensity from the key stratum; consequently, the effective cross−sectional retention rate of the roadway increases to 71.3%, confirming a substantial pressure relief effect, and the integrated technical framework of "mechanical mechanism analysis, key stratum positioning, and directional blasting for pressure relief" developed through this research provides a systematic and replicable solution for surrounding rock control in such challenging conditions, offering critical insights for rockburst prevention and the promotion of safe and efficient mining practices in coal mines with analogous deep, complex geology.