Study on Damage Characteristics and Engineering Application of Tunnel Cutting Blasting

To enhance excavation quality, optimize cavity-forming efficiency, and mitigate blasting-induced vibrations during tunnel cut blasting, this study investigates the influence of cut-hole inclination angle and millisecond delay time on rock damage evolution, taking typical Class IV surrounding rock (moderately weathered limestone) as the engineering background. A fluid–structure interaction (FSI) numerical model was established in ANSYS/LS-DYNA 19.0 incorporating the Holmquist–Johnson–Cook (HJC) constitutive model. Post-blast rock damage within the cut prism was quantitatively characterized using fractal box-counting dimensions. Based on rock dynamic fracture mechanics, an analytical model integrating crushed-zone formation (t1), crack propagation (t2), and fragment ejection displacement (t3) was established and subsequently validated through field tests using precision electronic detonators. The results indicate that among the investigated inclinations (55° to 70°), θ = 65° provides the optimal configuration by maximizing effective rock breakage and cavity volume (0.762 m3) within the cut zone while constraining overbreak. At this inclination, stress-wave superposition mechanisms favor an inter-hole micro-delay of 1.0~1.5 ms. In field tests where rock fragment kinematic displacement dominates cavity relief, an inter-hole delay of reduces the vertical peak particle velocity (PPV) by 63.2% (from 4.44 cm/s to 1.63 cm/s) and decreases the oversize boulder fraction (>800 mm) from 12.4% to 5.6%. This study provides both theoretical and practical support for the optimized design of wedge-shaped cut blasting in tunnels.