Optimization of smooth blasting parameters and damage mitigation in jointed rock mass roadways

During mine roadway excavation in jointed and fractured rock masses, drilling and blasting remains a widely adopted method. However, the complex interaction between blasting-induced stress waves and pre-existing structural planes often leads to overbreak, loosening of the surrounding rock, and an expanded excavation damage zone, posing significant challenges to roadway stability and construction safety. Most existing studies are limited to single-factor analyses or assume homogeneous rock mass behavior, leaving a critical gap in understanding the coupled effects of joint geometric parameters and blasting parameters on damage evolution. This study addresses this gap by developing a numerical model using LS-DYNA to investigate blast damage control in jointed rock masses during roadway excavation. A systematic parametric analysis was conducted to evaluate the influence of joint dip angle (α), joint thickness (h), joint position, and blast-hole spacing (d) on blasting performance. The results show that at α = 45°, particle vibration velocity at the monitoring points reaches its maximum, and fragmentation is most pronounced along the blast-hole connection line. Reducing the blast-hole spacing to 60 cm increases the peak effective stress at the joint plane to 72.8 MPa, yielding optimal fragmentation while mitigating excessive rock damage commonly associated with larger spacings. As joint thickness increases from 4 cm to 8 cm, the peak effective stress at the joint plane drops from 94.7 MPa to 70.8 MPa. This decrease of approximately 33.7% indicates that thicker joints substantially enhance stress-wave attenuation and energy dissipation. Moreover, increasing the distance between the joint and the blast hole from 5 cm to 15 cm significantly reduces damage in the rock mass between the source and the joint plane. Field validation demonstrates that the optimized smooth blasting scheme, compared to conventional blasting, improves the half-hole rate from 33.3% to 93.3%, increases the average advance per cycle from 2.43 m to 2.92 m, and reduces the depth of blast-induced damage from approximately 2.4 m to 1.5 m. These findings confirm that the proposed blasting parameters markedly enhance excavation quality and effectively limit blast-induced damage in jointed rock masses.