地应力水平对深埋隧洞爆破振动频谱结构的影响

爆破振动的频谱特性对隧洞安全施工具有重要意义。采用动力有限元方法,分析了不同地应力水平条件下围岩爆破振动频率特征,通过对实测爆破振动信号的时域和频域联合分析,研究了不同频带上的振动能量分布。结果表明,爆破振动的主频及各个振动能量优势频带都有随地应力水平升高而降低的趋势,伴随爆破破岩过程而发生的地应力瞬态卸载动力效应是产生这一现象的主要原因。地应力水平越高,爆破振动信号中20～100 Hz的低频振动能量比重越大。当爆区的地应力为20 MPa时,20～100 Hz频带内的振动能量可达到总振动能量的35%左右;当爆区的地应力为30～50 MPa时,20～100 Hz频带内的振动能量可达到总振动能量的50%以上。除地应力水平外,应力卸载速率及岩体的力学特性也对爆破振动主频具有显著影响,卸载速率越高,低频振动能量比重越大。卸载速率取决于掏槽爆破方式,直孔掏槽导致岩体应变能释放速率最高。岩体弹性模量越大,爆破振动的主频越高。

Effect of in-situ stress level on frequency spectrumof blasting vibration in a deep-buried tunnel

The spectral characteristics of blasting vibration is of great significance to the safety construction of the tunnel. By using the dynamic finite element method, the blasting vibration frequency characteristics of surrounding rocks under different ground stress levels are analyzed. And by combining with the time-domain and frequency-domain analysis of the measured vibration signals, the vibration energy distributions at different frequency bands are studied. The results show that the dominant frequency of blasting vibration and the superior frequency bands of vibration energy decrease with the increase of stress level. This phenomenon results mainly from the dynamic effect of the in-situ stress transient unloading in the rock blasting process. The higher the in-situ stress level, the greater the proportion of low-frequency vibration energy of >20 100 Hz in blasting vibration signals. When the stress of the blasting area is 20 MPa, the vibration energy of >20 100 Hz band can reach about 35% of the total vibration energy;when the stress of the blasting area is 30 50 MPa, the vibration energy of >20 100 Hz band can reach more than 50% of the total vibration energy. In addition to the stress level, the stress unloading rate and the mechanical properties of rock mass also have a significant influence on the main frequency of blasting vibration. The higher the unloading rate is, the greater the proportion of low-frequency vibration energy. The unloading rate depends on the cutting blasting mode, and the straight hole cutting leads to the highest release rate of rock strain energy. The greater the elastic modulus of rock mass is, the higher the dominant frequency of blasting vibration.