Abstract：Research purposes:There are many technical problems in design of the unequal span double－arch tunnel due to its special structure and complex construction technology．Taking the Xinzuofang Tunnel of the second line of the Suining － Chongqqing Railway as the engineering background，the study was done on the key design technologies for the unequal span double － arch tunnel under shallow biasing condition．
Research conclusions:Combined with construction of the Xinzuofang Tunnel，from the study on the key design，construction and waterproof and drainage technologies for the mid－partition wall structure of the unequal span double－arch tunnel，it is concluded: ( 1) During the construction of the unequal span double－arch tunnel，the mid－partition wall is always suffered from the dynamical unequal force，so its stability is crucial to the stability and security of the whole tunnel structure． ( 2 ) The three bench method of the mid － pilot tunnel－right tunnel－left tunnel is more available for construction of such kind of tunnel．(3) The waterproof and drainage technologies along with water blocking can effectively solve the water seepage on the top of middle－partition wall．The key technologies presented in this paper have been used in construction of the Xinzuofang Tunnel，achieving the expected result． The result can be as the reference to the similar works．
Zheng Zongxi，Sun Qiqing．Research on the Construction Technique of the Unsymmetrical Multi － arch and Unsymmetrically Loaded Railway Tunnel［J］． Journal of Railway Engineering Society，2012 (8) : 60－65．
Wang Xiaofang，Li Cunde，Song Yuxiang． Analysis of the Blasting Vibration Effect for Enlargement of Double － arch Tunnel ［J］． Journal of Shijiazhuang Railway Institute，2002(S) : 5－7．
Wang Jun， Xia Caichu， Zhu Hehua， etc． Site Monitoring and Analysis of Non － Symmetrical Multi － Arch Highway Tunnel［J］． Chinese Journal of Rock Mechanics and Engineering，2004(2) : 267－271．
Deng Jian，Zhu Hehua，Ding Wenqi． Finite Element Simulation of Whole Excavation Operation of a Unequal － span Double － arch Tunnel ［J］． Rock and Soil Mechanics，2004(3) : 477－480．
Wang Wei，Huang Juan，Peng Limin，etc． Analysis on the Structure Stability of the Unsymmetrically Loaded and Connecting － arch Tunnel Caused by Different Construction Orders ［J］． West － china Exploration Engineering，2004(10) : 105－108．
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Shen Yusheng， Zhao Yuguang． Site Monitoring and Analysis Reseach on Surrounding Rock Deformation of a Biased Double － arch Tunnel［J］．Highway，2005(4) : 194－198．
2013, Vol. 30 
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