Blasting in Twin Tunnels with Small Spacing and Its Vibration Control

摘要

The paper introduces the practice of blasting operation in closely spaced twin tunnels and its safetyrncontrol on blast vibration in Shenzhen, China. The twin tunnels, separated by 13.5 meters, run eastwardrnin parallel. The excavation of the south tunnel started after the north tunnel had been completed for eightrnyears and opened to traffic onwards. To determine the influence of the construction of the south tunnelrnon the traffic safety of the north one, 2D numerical simulation of the blast vibration field in north tunnelrnwas conducted by ADINA software and finite element program in advance and during the excavation.rnThe field measurement and numerical analysis prove that stability of the north tunnel can be maintainedrnif the Peak Particle Velocity (PPV) is limited within 8 cm/s. In the initial excavating stage a series of trialrnblasts and vibration monitoring throughout the whole excavation were carried out to obtain the data andrntimely feedback to modify the blast design accordingly. The results of monitoring indicated that the PPVrnat the concrete lining close to the blasting site were successfully kept below 6 cm/s by taking a series ofrneffective measures. In this way both the traffic safety of the existed tunnel and the on schedulerncompletion of construction of the south tunnel are ensured.