Propagation and Attenuation of Blast Vibration Waves in Closely Spaced Tunnels: A Case Study

The closely spaced tunnels structure has been widely used in traffic tunnels, hydropower stations, collieries and underground metal mines. Blasting has important implications for the construction of these closely spaced tunnels. Due to the effect of multi-free surfaces and the appearance of excavation damaged zones (EDZs), the propagation and attenuation of blast vibration are expected to be more complex than in ordinary separated tunnels. In this study, field tests including ultrasonic tests and vibration tests were conducted during the excavation process of a closely spaced tunnels project, then a series of three-dimensional dynamic calculations considering explosive velocity detonation were conducted to study the propagation and attenuation of blast vibration. The results indicate that in closely spaced tunnels, EDZs have evident amplification effects on the vibration intensity, especially on the Rayleigh waves propagating longitudinally. The small clear distance and larger dimensionless wavenumber lead to the asymmetric distribution of vibration velocity, and the side wall located in the wave incident side is more easily damaged. In tunnel blasting, the maximum Peak Particle Velocity often appears around the heading face, while the maximum value appears at 1.5–3.0 m behind the heading face section for adjacent tunnels. The results of this study can be applied in the design of blasting and monitoring scheme of closely spaced tunnels.