Abstract: To improve the fire prevention and control level of superlarge section steel shell immersed tunnels in China, a case study is conducted on the ShenzhenZhongshan link immersed tunnel and the fire resistance limit standard of the tunnel is studied using thermalmechanical coupling simulation and material property test. When conducting the fire resistance test of the pipe joint structure and pipe joint, the weak links of the fire prevention structures, such as keel and seam, are considered and the corresponding fire protection technical scheme is introduced. The main conclusions are as follows: (1) The maximum temperature of the inner steel shell of the structure should be controlled within 300 ℃ in case of a fire. (2) The time for OMEGA rubber under 70 ℃ and 100 ℃ shall not exceed 2 and 1 h, respectively, and the maximum temperature shall not exceed 150 ℃. (3) The time for GINA rubber under 100 ℃ shall not exceed 1 h, and the maximum temperature shall not exceed 150 ℃. (4) The pipe joint structure can use a 35mmthick singlelayer fireproof board and an Lshaped joint, and the joint surface is coated with a thermal expansion adhesive. (5) The pipe joint can adopt a doublelayer fire protection system with a 35mmthick fireproof board and a 50mmthick ceramic fiber blanket. The free end of the keel is 500 mm, and the joints are sealed using fireproof glue.

Key words: ShenzhenZhongshan link, immersed tunnel, steel shellconcrete structure, fire resistance limit, fire resistance test, fire protection scheme