Vibration characteristics, attenuation law and prediction method in the near field of tunnel blasting

Vibration induced by near-field tunnel blasting can easily damage the surrounding rockmass. The vibration response, damage characteristics and attenuation law in front and rear of the tunnel face were studied under different types of holes blasting. A new prediction method for the near field PPV was proposed based on the far field monitoring data. The results showed that the maximum PPV of the surrounding rockmass near the tunnel face was generated by the peripheral holes blasting, and the propagation distance was the key influencing factor. In contrast, the maximum PPV away from the tunnel face was generated by cutting holes blasting, and the conditions of blasting free face and the charge weight had a greater influence than the propagation distance. Due to the cavity amplification effect of the excavated tunnel behind the tunnel face within a certain range of 2-6 m, the blasting seismic wave produces superposition in the vault behind the tunnel face. The vault PPV behind the tunnel face attenuated rapidly in the range of 0-2 m, then increased slightly in the range of 2-6 m, and then decreased slowly with the increase of propagation distance. By introducing the amplification coefficient, a modified formula was proposed to predict the near field PPV using the far-field monitoring data, which had effectively improved the prediction accuracy.