Study On Blasting Technology Of Tunnel Passing Underneath Subway Tunnel

In recent years, with the sustained and rapid development of economy in our country, urban transportation is more and more booming. Modern cities are usually congested and the supply of space becomes an emerging issue. During the construction of subway tunnel, it often happens that a new tunnel passes beneath buildings, existing pipelines or subway tunnels. And the most typical one is that a new tunnel passes beneath an existing tunnel. Limited by geological and engineering conditions, drilling and blasting method is commonly adopted for the excavation of a new tunnel. However, blasting vibration will possibly jeopardize the safety of the existing tunnel. So how to control blasting vibration becomes a hot engineering issue, and the research on technology of blasting is of significance when a new tunnel passes beneath an existing tunnel at a close distance.This paper is based on the tunnel project in YiTian Road, part of Guangzhou-Shenzhen-Hong Kong Passenger-dedicated Railway Line, focusing on the project that the new tunnel cross beneath Line 3 of Shenzhen Metro at a pretty close distance. The major achievements are as follows:(1)Through blasting experiments conducted in lower bench of the new tunnel, it proves that ① an attenuation law for vibration velocity in the close zone is obtained-V= 324.6×(Q/R)1.31. There exists much difference compared with the empirical formula proposed by Sakowski, which proves that the Sakowski empirical formula doesn’t function well in the close zone. ②through analyzing on the waveform measured in the close zone, the extent of vibration period for a single hole blasting is 10ms～30ms, the main frequency of vibration is related to the explosive blasting simultaneously, the explosive becomes larger, the vibration turns larger and the main frequency of vibration turns smaller.(2)Detonating blastholes one by one using electronic detonators will be of great help to reduce vibration velocity and increase the main frequency of vibration, this paper studies the principle, analyzes the delay for electronic detonators in two aspects and gives the method to calculate the minimum delay suitable for control blasting vibration.(3)The blasting scheme of upper bench is as follows:dividing the whole section one-time blasting into multiple blasting, adding hollow holes of large diameter and detonating blastholes one by one using electronic detonators are applied, so that reducing the explosive simultaneously blasting, decreasing vibration velocity and increasing the main frequency of vibration are achieved.(4)By analyzing on the vibration data measured in the existing tunnel, conclusions are obtained: ①vibration velocity in vertical direction is larger than vibration velocity in horizontal and longitudinal direction, and has a dominant influence on the existing tunnel. ②vibration velocity ahead of heading face is larger than vibration velocity back of heading face. ④The measured data is consistent with prediction of empirical formula.