Theoretical model and numerical analysis of millisecond delay time of parallel cut blasting in tunneling excavation

摘要

In tunneling excavation engineering, the cut blasting is a main factor affecting the utilization ratio of the holes. The parallel cut blasting method with the large diameter empty hole is now widely used in tunneling blasting because of the application of the large-sized equipment. The cutting provides the free cavity for post-blasting. After blasting the rock in the cut area is broken, meanwhile, the broken rock pieces are mixed with the explosion gases into a two-phase fluid that is thrown out from the cut cavity, the time is needed in this process. If the split-second delay time between the cut blasting and post-blasting is too short that the broken rock pieces are partly thrown out, the blasting efficiency is bad. The fewer the rock pieces remain in the cut, the better the blasting result is. In this paper, the mechanical model of initiation delay time for parallel cut blasting is set up by analysis of rock pieces movement in the cut cavity, and the model is available to optimize the initiation delay time. The model is available to find out the quantitative relationship of clearage rate (the volume ratio of the remained rock pieces in the cut cavity) and time, and to optimize the initiation delay time between the crumbling holes and the cut-borehole. The numerical calculation shows that the interval delay time between the cut-boreholes and the crumbling holes should be taken in 17-25 ms per meter of the borehole depth according to the rock quality. In engineering applications, the split-second delay time of parallel cut blasting in rock drifting should be taken according to the rock quality that the delay time is 70-100 ms when the depth of cut borehole is 4 m, 50-80 ms for the depth 3 m, and 30-50 ms for the depth of 2 m, respectively.