Abstract: The water supply system outside the tunnel is always frozen and the in-tunnel pipe network is always over-pressurized during extra-long highway tunnel construction (10 to 20 km) in high attitude and cold areas. Thus, a case study is conducted on the Tianshan Shengli tunnel of the Urumqi-Yuli expressway. The normal high pressure water supply system outside the tunnel and the stable high pressure water supply system in the tunnel cannot be effectively implemented. Based on the difficulties in firefighting design of this tunnel, a firefighting design scheme of setting high-level reservoir in tunnel and sectional water supply of pipe network is proposed and discussed in detail. The following conclusions or suggestions are given: (1) The normal high pressure water supply system is beneficial for water supply of extra-long tunnels in high attitude and cold areas. (2) In-tunnel high-level reservoir is recommended. (3) The number, setting distance, and setting attitude of the high-level reservoir built in tunnel can be determined according to the length and slope of the tunnel and related hydraulic calculation results. (4) The normal high pressure water supply system with in-tunnel high-level reservoir successfully addresses serious overpressure of pipe network. These demonstrate that the normal high pressure water supply system with in-tunnel highlevel reservoir is safe, reliable, economic, and environmentally friendly.

Key words: Tianshan Shengli tunnel, high level reservoir in tunnel, firefighting and water supply system, pipe network, overpressure