Abstract:

 Clarifying the vibration response and cumulative damage evolution law of an interlaid rock column in a large span tunnel with a small clear distance under dynamic blasting loads can better ensure the tunnel construction and stability of surrounding rock. Hence, a case study is conducted on the Xiamen Haicang Shugang channel project, where onsite blasting vibration measurement and acoustic wave test are adopted to conduct monitoring and analysis on the blasting vibration and borehole wave velocity of the interlaid rock in the small clear distance section, and the original blasting plan is optimized. Furthermore, the law of vibration propagation and damage evolution of the interlaid rock under the effects of cyclic blasting is explored. The results show the following: (1) Amount of charging of the cut and the number of free surfaces are the main factors affecting the vibration velocity of the interlaid rock blasting. The vibration velocity of the interlaid rock is reduced by 67.4% by optimizing the vibration reduction hole setting in the optimized blasting scheme, and the maximum mass peak vibration speed of the interlaid rock is 12.67 cm/s, which conforms to the specification requirements. According to the Sadowski formula, the vibration response law of the interlaid rock is obtained. (2) Under multifrequency blasting, the acoustic wave velocity of the side rock mass is higher than that of the middle rock mass. Due to the combined effects of stress wave and cracks, the wave velocity of surrounding rock shows a fluctuating downward trend from the inside of the interlaid rock to the tunnel contour. When moving away from the tunnel face, the cumulative damage range of the interlaid rock is eventually stabilized within 1.5 m of the surrounding rock surface. Through onsite monitoring and optimization, the blasting vibration control of the interlaid rock and the judgment of the cumulative damage range are realized, which ensures efficient and safe excavation of largespan bifurcated tunnels.

Key words: largespan and smalldistance tunnel, interlaid rock, acoustic wave test, blasting vibration measurement, damage range, Haicang Shugang channel, bifurcated tunnel