Field and numerical investigation of multi-hole delay regulation for blast vibration and rock damage control

Reasonable delay-time determination in millisecond blasting is essential for controlling blast-induced vibration and improving blasting performance. However, numerical delay times cannot always be directly applied to field production blasting because of the discrepancy between simulated and measured waveforms. In this study, a field waveform-driven delay-time determination method was developed by combining single-hole field blasting tests, waveform superposition, LS-DYNA simulation, and production blasting feedback. Representative source waveforms were obtained from open-pit bench blasting tests, and a corresponding numerical model was established to analyze delay-dependent PPV response, energy distribution, and source-region rock damage. By comparing the effective waveform durations of simulated and measured single-hole signals, a site-specific simulation–field delay-time mapping ratio of 1:5.65 was obtained. Based on waveform superposition and numerical analysis, a favorable delay range of 6–12 ms was identified for multi-hole blasting under the investigated source-region conditions. Considering the production blasting practice at the mine, eight-hole field blasting tests with delay times of 0, 10, and 20 ms were further conducted to preliminarily investigate the influence of delay-time setting on PPV control and fragmentation performance. The results showed that the 10 ms delay reduced the PPV at the underground protected roadway and achieved better fragmentation control under the tested production conditions. This study provides a practical reference for delay-time design, vibration control, and blasting performance optimization in open-pit bench blasting, and offers a basis for further studies on the influence of surface blasting on underground protected structures.