Research on blasting technology for construction of Fenghuoshan tunnel in permafrost

The Fenghuoshan Tunnel is an important project in Qinghai-Tibet Railway. How to protect permafrost during tunnelling construction is one of key technologies. There are two kinds of influences on permafrost because of the blasting construction: (1) firstly, blasting results in the damage of the surrounding rock, producing cranny in surrounding rock or making existed cracks spreading even connecting; (2) secondly, the explosion produces gas with high temperature and high pressure, tremendous heat energy influences the heat balance of permafrost. To minimize the effects on permafrost during explosion construction, the research on relevant explosion scheme is conducted based on the theoretical analysis and in-situ test. Presplitting blasting is adopted in the hollow segment; and smooth blasting is adopted in the tunnel body segment. The whole section excavation is considered in the tunnel body segment with surrounding rock grade IV; and the face step excavation is adopted for the tunnel body segment with surrounding rock grade V. Explosion parameters were optimized finally. The maximal explosion vibration velocity in the surrounding rock is controlled at 5-10 cm/s. To solve the heat disturbance problem, brine mud is adopted to block up explosion holes for cool and dustproof. The research result indicated the explosion gaseous cool effect when the brine mud medium was adopted reached 70% compared with 55% when the water mud medium was adopted, so the gaseous cool effect was significant.