Study on the failure effect of gas tunnel blasting considering the influence of delay time and its engineering application

The reasonable delay time setting is the key factor affecting the blasting effect of gas tunnel. To this end, we have introduced a digital electronic detonator that can be freely set on site. Through theoretical analysis, we obtained the time required for the rock mass to be completely thrown out in the cutting area, revealed the law of rock mass movement by numerical simulation, and further proposed a blasting effect evaluation method and carried out engineering application. The results show that the optimal initiation time of the cutting area is 40ms, and the migration law of rock mass can be divided into three stages: crack propagation, volume increase and rock mass ejection. According to the optimal delay time in the cutting area, the optimal initiation time between each row of blast holes was determined to be 0ms, 40ms, 60ms, 80ms, 100ms, and 120ms, respectively, and a blasting effect evaluation system including blasting effect index K and circumferential flatness σ was established. Finally, a field test was carried out in a plateau gas tunnel. The statistical characteristics of the blasting effect show that after optimizing the delay time, the half-hole rate after blasting is above 90%, the linear average over-excavation is within 20 cm, and the circumferential flatness σ is 2.9 cm. The contour control accuracy is high, and the particle size distribution of the blasting pile is reasonable, which provides a reference for similar engineering blasting.