Mechanism of stress transfer in directional blasting and optimization of design parameters

ObjectivesThis study addresses the significant threat posed by the continuous variation of stress fields under mining activity to the stability of waterproof coal pillars and the safe mining of working faces， particularly when faults are present within the coal pillars.MethodsTaking the 3309 working face of Hebi Zhongtai Mining Co.， Ltd. as the engineering geological context， theoretical analysis， orthogonal experiments， and FLAC3D numerical simulations were conducted to investigate the factors influencing stress transfer via directional blasting and the internal stress distribution characteristics of waterproof coal pillars under varying roof-cutting depths and angles.ResultsThe findings indicate that as the roof-cutting angle and depth increase， vertical stress shifts deeper into the coal pillar. However， beyond a certain threshold， further increases in roof-cutting depth or angle have minimal impact on the location of the stress concentration zone and the peak vertical stress. Among the tested schemes， when the roof-cutting depth is 15 m and the roof-cutting angle is 15°， the stress concentration zone is farthest from the return airway， with a maximum distance of 19.76 m， and the stress peak is minimized at 15.65 MPa.ConclusionsDirectional blasting effectively facilitates stress transfer by cutting the roof and relieving stress， thereby isolating the overlying strata of the return airway from the surrounding rock layers of the waterproof coal pillar. This redirects stress near the return airway deeper into the pillar， mitigating the impact of mining activities. On-site industrial experiments validated the feasibility of the selected parameters （roof-cutting depth of 15 m and angle of 15°）， demonstrating that stress transfer was successfully achieved. The proposed method significantly enhances the stability of waterproof coal pillars， meeting the requirements for safe production. These findings provide a valuable reference for the stress transfer protection of fault-affected waterproof coal pillars under similar geological conditions.