Blasting Technology Research in Construction of Fenghuoshan Tunnel in Permafrost

The Fenghuoshan Tunnel is an important project in Qinghai-Tibet Railway. How to protect permafrost during tunnelling is one of key technology. There are two kinds of influences on permafrost because of the blasting construction, firstly, blasting results in the damage of the surrounding rock, producing cranny in surrounding rock or making existing cranny spreading even connecting, secondly, the explosion produces gas with high temperature and high pressure, tremendous heat energy influences the heat balance of permafrost. To minimize the effect on permafrost during explosion construction, this paper has done research for relevant explosion scheme based on the theoretic analysis and spot tests. Pre-crack explosion is adopted on the hollow segment, and smooth explosion is adopted on the tunnel body segment, whole section excavation is adopted on the tunnel body segment with grade Ⅳ surrounding rock, and the face steps excavation is adopted on the tunnel body segment with grade Ⅴ surrounding rock. Explosion parameters were optimised finally. The maximal explosion vibration velocity in the surrounding rock is controlled in 5～10 cm/s. To solve the heat disturbance problem, brine mud is adopted to block up explosion holes in order to coll and dustproof. The research result indicated the explosion gaseous cool effect when the brine mud medium as adopted reached 70% compared to 55% when the water mud medium was adopted, so the gaseous cool effect was very distinct.