Parameter calculation of the initiating circuit with mixed use of nonel detonators and electronic detonators in tunnel controlled-blasting

This paper proposes a parameter calculation method for the mixed initiation circuit with both nonel detonators (NDs) and electronic detonators (EDs) to increase the detonator delay for reducing the blast-induced vibration in tunnel blasting and to ensure safe circuit operation. The circuit involves the outside-hole delay for increasing the delay numbers under the premise of safe circuit operation. The time calculation and vibration-reduction effects of the circuit were quantitatively determined through mathematical modeling and field experimental studies. A calculation model of mixed detonator groups was established based on three constraint conditions: no delay irregularly, no misfire, and an increased delay number. The main parameters obtained were the initiation sequence of the EDs, the delay number of the NDs and the time interval of the EDs inside the blastholes. The factor considered in the mathematical modeling was the delay error of the NDs. The calculation results agreed well with experimental results, the latter confirming that the mixed initiation circuit was feasible and safe when using a 90 ms delay outside the blasthole. In addition, the delay numbers of the mixed-detonator group were increased by 40% relative to those of NDs. Compared with conventional blasting that reduces the advance per round, blasting with the mixed initiation circuit using an outside-hole delay produced 82.3% less blast-induced vibration. It was also found that the blasting cost could be reduced by 54.3% compared with that of using EDs only. Overall, the mixed initiation method had a positive effect on tunnel controlled-blasting. The research methods and results are expected to be useful in guiding related engineering efforts.