隧道爆破新自由面形成时间的识别与应用

Identification and application of the formation time of new free surface in tunnel blasting

隧道爆破中新自由面的形成影响爆炸能量的传播,能显著降低爆破振动强度。由于现场爆破过程的瞬态性及危险性,难以确定新自由面的形成时间,揭示其作用规律。为解决该问题,提出新自由面形成时间的识别方法,借助电子雷管精准起爆特性设计获取两组对比波形,一是通过现场短延时掏槽爆破试验获取受新自由面影响的实测振动波形;二是按照现场延时间隔,基于叠加理论得到不考虑新自由面影响的计算振动波形。通过希尔伯特黄变换(Hilbert-Huang transform,HHT)分别计算两组波形全时程的累积能量,分析两条累积能量曲线,以差异特征点作为新自由面形成时间。现场应用该方法确定的形成时间为43.5 ms。分析新自由面形成后能量折减率的变化过程,发现存在快速增加到最大值、持续稳定、逐渐降低3个阶段。对比分析短延时(<10 ms)和长延时(>10 ms)爆破条件下的计算振速和累积能量,确定16~19 ms为较优的掏槽孔间延时。

The formation of new free surface in tunnel blasting has an important influence on changing the explosive energy release process in the cutting area,which can significantly reduce the blasting vibration intensity.However,it is difficult to obtain the accurate formation time of new free surface due to the transient nature of the blasting process and the great difficulty in testing.A method to identify the formation time of new free surface was proposed:two groups of contrast waveforms were obtained based on the precise initiation characteristics of electronic detonator.The two groups of waveforms were as follows:measured vibration waveform affected by new free surface was obtained by short delay cut blasting test;calculated vibration wave was obtained based on the superposition theory according to the initiation time sequence,without considering the influence of new free surface.The accumulated energy of two groups of waveforms was calculated by Hilbert-Huang transform(HHT),and the difference characteristic points were taken as the formation time of new free surface.The formation time derived by this method was 43.5 ms.After the formation of the new free surface,there are three stages:rapid increase to the maximum,continuous stability and gradual decrease.By comparing and analyzing the calculated vibration velocity and cumulative energy under the condition of short delay time(10 ms) and long delay time(10 ms),it is concluded that 16-19 ms is the best delay time between cut holes.