| Since1896immersed tube tunnel was built in the USA for the first time，it has ahundred years of history. In China, the research on immersed tube tunnel started quitelate about60’s of last century. However，until now about dozens of tunnels have beenbuilt in Hongkong, Guangzhou, Shanghai, Ningbo, Tianjing, Taiwan and other placesone by one since then.While immersed tube tunnel spans the sea or river and brings convenience topeople, fire as a major disaster of tunnel also occurs frequently. Owing to its structurefeature in pipe joint and segment joint, which needs have the ability of water tightnessand flexibility and usually uses the rubber, the temperature range of its normal work islimited. At the same time, undersea immersed tunnel locates on deep sea or river. Soonce the fire occurred, it will result in the tunnel beyond repaired.The project of Hongkong-Zhuhai-Macao Bridge acts as a tie and communicates onTwe Shores and Three Places. The traffic flow is large and most of the vehicles arecross-boundary vehicles. While the tunnle has characters of closed，narrow，escape andrescue difficulty etc. Once fire occurred in immersed tunnel, it can cause severecasualties and huge economic losses, but also can cause huge social influence. it isnecessary to carry out research abou temperature curve and fire resistance design targetof immersed tunnel. Then put forward the suitable fire protection scheme for the jointand structure of immersed tunnel. It has considerable importance on theoretical andpractical significance for fire protection of immersed tunnel.This paper bases on the national science and technology support program The keytechnology of offshore Special immersed tunnel construction and disaster preventionand mitigation and does the following several aspects work mainly:⑴According to the structure characteristics of immersed tunnel, fire resistanceperformance of immersed tunnel structure and joints are considered respectively and theundersea immersed tunnel fire-resistant target is determined. The temperature of thebottom of concrete structure component and the rebar must be controlled under380℃and250℃(HC curve) or380℃and300℃(RABT curve),while the outsidetemperature of fire is some1200℃. And the joint temperature of tunnel must becontrolled under70℃.⑵Then take some survey about fire protection technology of domestic andforeign and carry out the evaluation of the applicability for fire protection technology.⑶Track the high-temperature test platform and accomplish it. Then a list number of tests with different concrete component and different fire protection scheme are done.Finally the proposal fire protection scheme for immersed tube tunnel is decided. Theproposal is that2×1cm fireproof board for concrete structure component. When itcomes to joints, it is2×1fireproof board with a layer of fireproof cotton plus4×1cmfireproof board as fire-resistivepartition.⑷Numerical computation is performed for the immersed tunnel structure andjoint. It is accomplished that the heat is transmitted from fluid to solid and back to fluid,at the same time, the heat transfer mode from convection to conduction and back toconvection and radiation.⑸Finally the recommended fire protection scheme is decided and optimized withthe consideration of numerical calculation and high temperature test.Research shows that;⑴On HC or RABT curve for two hours, the structure can adopts the fireprotection scheme of2×1cm fireproof board. While, the joint of immersed tube tunnelcan adopt2×1fireproof board with a layer of fireproof cotton plus4cm fireproof boardas fire-resistivepartition. The scheme can meet the basic refractory designed target.⑵Test also shows that the performance of fireproof board is significantly lowerwhen it on fire for70min. So it should be considered on actual project and the boardshould be replaced under fire for1h or more.⑶At the same time, consider the impact force of fire flame，it can cause influenceon the fireproof board of tunnel joint. So it must be reinforced with steel frame, then theinfluence of fire protection caused by mechanical injury of fireproof board which iscaused by the impact force of flame. |
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