A maximum velocity mapping approach for damage prediction in underground tunnelling destressing blasting

Near-field peak particle velocity (PPV) is widely used as a criterion for underground blasting damage during tunnel development, typically supported by site-specific thresholds. In this study, a method based on maximum velocity mapping is proposed to bridge the gap between empirical, particle velocity-based approaches and advanced computational modelling. The proposed approach has been initially validated with fully instrumented blasting experiments conducted by the NIOSH group. Following this, numerical studies using HSBM were conducted for multi-hole tunnel development destressing scenarios. Results showed that the proposed method effectively captures the three-dimensional damage envelope, accounting for the influence of charge interactions and boundary conditions. A comprehensive sensitivity analysis was then performed based on an actual underground tunnelling destressing blast scenario to evaluate the effects of key blasting parameters, including initiation point, velocity of detonation, charge length, and potential timing scatter. The results indicate that destressing blasting performance is strongly governed by the blasting parameters, which significantly influence the damage profile and the volume of the damaged zone. Under the destressing scenario in this study, middle initiation produces a damage zone volume 10.6 % larger than bottom initiation. Increasing the detonation velocity from 3,000 m/s to 5,000 m/s results in a 41.8 % increase in damage volume. Similarly, charge length from 2 m to 6 m leads to a 215.4 % damaged volume increase. The proposed method uniquely integrates PPV-based damage criteria with physics-based numerical modelling to enable quantitative prediction of 3D blast damage zones and systematic evaluation of key blasting parameters for optimising destress blasting design.