Study on influence of blasting vibration on cross tunnels with small clearance

A new tunnel was built to cross over the existing tunnel.The smallest clearance was 8.1 m between the upper and lower tunnels.The effect of blasting that the newly-built tunnel exerted on the existing tunnel structure was evaluated by numerical simulation method.It was indicated that when the rock was blasted with the full face method at a distance of more than 10 m to the cross point,the impact acting on the existing tunnel was relatively small.On the other hand,when the distance was less than 10 m,the vibration speed of the second lining of the existing tunnel exceeded the standard.While the rock was blasted with stepped method,the new tunnel could cross over the existing tunnel safely.