Study on Attenuation Law of Blasting Vibration in a Small Clear Distance Highway Tunnel

In order to study the vibration response of the interlaid rock in the small clear distance tunnel under the blasting load, a field blasting vibration test was carried out based on the blasting project of the Xiaolongmen tunnel. The improved variational mode decomposition(VMD) and multi-scale permutation entropy(MPE) algorithm were employed to denoise the blasting vibration signal. Subsequently, the differences in vibration characteristics between the left arch waist(non-interlaid rock area) and right arch waist(interlaid rock area) of the tunnel were analyzed, along with a comparison and analysis of seismic wave attenuation characteristics generated by cut hole blasting and surrounding hole blasting. The results demonstrate that the improved adaptive VMD-MPE algorithm enables automatic determination of modal number K and penalty factor α while effectively eliminating noise from the vibration signal, reducing subjective decision-making influence. During posterior excavation tunnel face blasting, interlaid rock exhibits significant amplification effects on blast vibrations. Peak particle velocity(PPV) values are higher in interlaid rock compared to non-interlaid areas. However, vibrations attenuate faster within interlaid rock regions. Additionally, analysis reveals that low-frequency vibrations below 40 Hz account for a substantial proportion of energy within interlaid rock areas when comparing frequency characteristics at measuring points between non-interlaid and interlaid regions. Attention should be given to these low-frequency vibrations as they are more likely to induce resonance in supporting structures, posing higher risks of damage or destruction within interlaid rock zones. By analyzing the blasting vibration characteristics of the cut hole and the surrounding hole, it can be found that the vibration velocity generated by the surrounding hole blasting in the surrounding rock behind the tunnel face is greater than that of the cut hole blasting within the range of the scale distance(SD) which is less than or equal to 11.57 m kg^1/3 due to the effect of 'corner weakening' and the influence of the seismic wave propagation path. After exceeding the critical value of SD, the vibration velocity generated by the cut hole blasting is greater.