Mechanism and Application of Partial Weakening by Deep-hole Blasting in Hard Rock Roadways of Coal Mines

Mechanical excavation methods have increasingly supplanted blasting techniques in coal mine roadway development. Nevertheless, when encountering hard rock formations, these methods exhibit significantly reduced excavation efficiency coupled with accelerated cutting tool wear. Therefore, this underscores the critical need to develop cost-effective auxiliary rock-fragmentation technologies to optimize mechanical excavation performance. Mechanistic analysis of cutterhead-rock interaction reveals that reduced excavation efficiency results from triaxial failure induced by in-situ stress fields. Furthermore, higher in situ stress magnitudes correlate with increased rock fracture resistance. Progressive cutterhead penetration alters the stress state from triaxial to uniaxial confinement, fundamentally changing the rock failure mode. Higher in-situ stress facilitates rock mass failure. A local stress evolution model was developed based on the Mohr-coulomb criterion. Theoretical calculations demonstrate that for hard rock with 86 MPa uniaxial compressive strength at 300 m depth, the required cutting pressure decreases from 139.5 MPa to 64.2 MPa under two rock-breaking conditions, representing a 54% reduction. To achieve this improvement, a localized deep-hole blasting method for weakening hard rock is proposed. Numerical simulations were conducted to analyze the effect of the empty holes on rock mass blasting damage, leading to the determination of an optimal deep-hole blasting scheme. Field tests at Taitou Qianwan demonstrated the technology′s effectiveness, producing a uniform fragmentation zone approximately 40 cm in diameter and increasing excavation efficiency by 78%. This safe and controllable weakening technique delivers significant results, providing both theoretical foundations and practical solutions to enhance hard-rock roadway excavation rates.