Vibration reduction technology and the mechanisms of surrounding rock damage from blasting in neighborhood tunnels with small clearance

Interlaid rock is an important component in the construction of neighborhood tunnels that supports and reinforces the area between two tunnels. However, the blasting load during excavation can sometimes damage the interlaid rock and threaten the stability of a tunnel's structure. This paper presents a case study of the small clearance section of the Liantang highway tunnel project in Shenzhen, China, where the minimum distance between the two tunnels involved is only 0.5 m. To reduce the damage to the interlaid rock caused by blasting loads, we proposed a four-part excavation method with a vibration-cushioning rock layer in the following tunnel of neighborhood tunnels. Numerical simulation was used to model the damage prevention mechanism of the vibration-cushioning rock layer and to better understand the propagation of cracks in the interlaid rock. Furthermore, based on the simulation results, combined microseismic controlled-blasting technology was implemented, using innovative blasting patterns combined with different charge structures and blasting equipment designed according to the varying thickness of the interlaid rock. Finally, this implementation succeeded in protecting interlaid rock during blasting operations.