Abstract: Herein, the source characteristics of noise at the tunnel entrance during blasting and attenuation patterns of the peak sound pressure level outside the tunnel are investigated. High-precision acoustic sensors are deployed to monitor the blasting noise. The Hilbert-Huang transform is applied on field monitoring data to analyze the time-frequency-energy characteristics of blasting noise signals. Regression analysis is first employed to determine a formula for predicting the peak sound pressure level of noise outside the tunnel during blasting of the tunnel entrance. Results reveal that: (1) The tunnel blasting noise signal exhibits typical pulse characteristics, with instantaneous energy peaks corresponding well to amplitude peaks. Energy is mainly concentrated within 0.2 s after the arrival of the first wave. (2) Blasting noise at the tunnel entrance has a wide frequency band but concentrated energy distribution in a narrow band below 110 Hz with multiple frequency peaks. Significant lowfrequency characteristics of the blasting noise render conventional sound barriers ineffective. (3) Distinct models are used for predicting peak sound pressure levels of noise outside the tunnel between entrance and main tunnel blasting. When applying mining bench blasting prediction formulas to the entrance blasting, the relative errors of predictions remain below 1.78%. Reducing the maximum charge per delay can effectively reduce the peak sound pressure level of the blasting noise.

Key words: tunnel blasting, blasting noise, frequency, Hilbert-Huang transform, sound pressure level