Determination method of tunnel blasting parameters using electronic detonator under changing condition of free surface

Abstract

The technical potential of electronic detonator has not yet been fully utilized in tunnel engineering. An important reason is that there is no calculation method of blasting parameters supported by rigorous theory. The pivotal blasting parameters such as charge and delay time, etc. are mostly designed following ordinary mining method. And it can not solve the problem of calculation accuracy of blasting parameters after the formation of the second free surface. Taking Guanyinqiao Tunnel in Chongqing as the research background, based on the Anderson principle and the delay characteristics of the electronic detonator, a new method for designing the blasting parameters of electronic detonator is proposed under the different free surface conditions changing in the process of tunnel blasting, from single free surface to dual free surface. Firstly, based on the single-hole and single free surface blasting vibration curves of different charges acquired on site, the superimposed vibration of multiple blast-holes under each delay time was calculated one by one. After comparing the superimposed vibration curves of different charges and delays, it was determined the blasting parameters of single free surface, including the maximum single-hole charge and the optimal inter-hole delay. Secondly, according to the characteristics of the electronic detonator, the short-delay cut blasting field test was designed. By comparing the calculated waveform without considering the influence of the second free surface with the measured waveform affected by the vibration reduction effect of the second free surface, it was found that the second free surface had formed at 48 ms after initiation. Based on this, a single-hole blasting test was designed after the formation of the second free surface. By calculating the superimposed vibration velocity based on the single-hole waveforms before and after the formation of the second free surface, it was determined the blasting parameters under the dual free surfaces condition, including single-hole charge, inter-hole delay time, and delay between different types of holes. Finally, the calculation method of blasting parameters in the whole blasting process was formed. After the comprehensive analysis of the calculated results, the single-hole charge of the main cutting holes is 1.2 kg, and it is 1.4 kg of the auxiliary cutting holes, then the delay time between holes is 5 ms on site; the minimum delay time between the main cut holes and the auxiliary cut holes is 35 ms. The field test was carried out with the optimized parameters mentioned above, and it got high-efficiency footage as well as a low vibration velocity.