Abstract：Research purposes: During the construction of the railway terminal，when the new or additional railway under － passes the existing road bridge，the factors that affect the safety of existing bridges should be considered carefully in the design and the safety of the existing bridge becomes an important issue in the railway construction because the construction condition is limited． On considering the technical and economic factors， the design schemes for Chongqing －Fuling Railway under － passing the Wutong Overpass Bridge in Chongqing were compared and the best scheme was selected to reduce the negative factors that affected the safety of the bridge for the purpose of providing the references to the similar works．
Research conclusions: In general，when a new or additional railway under － passes the existing road bridge，the scheme should be reasonably selected on consideration of economic，technical，security and other factors． Minimizing the impact of construction of a new or aditional railway on the existing road bridge is crucial to construction of a new or additional railway under － passing the existing road bridge ． The pile － board structure was used for construction of Chongqing －Fuling Railway under － passing the Wutong road bridge to transfer the top load to the bed rock by the pile． In this case，the safety of existing bridge and the stability of the existing subgrade can be ensured ． This scheme is the best one because of minimizing the impact of railway construction on the existing road bridge．
Wei Yongxing． Study on Pile － slab Structure Subgrade for Ballastless Track of Passenger Dedicated Line［J］．Journal of Railway Engineering Society，2008( 4) : 19 －22．
［2］ TB 10001—2005，铁路路基设计规范［S］．
TB 10001—2005，Code for Design on Subgrade of Railway［S］．
Su Qian． Design and Analysis on Pile － Board Structure of Deep Collapsible Loess Ground along Zhengzhou －Xi＇an Passenger Dedicated Railway Line［J］． Railway Construction Technology，2007( 2) : 1 － 4．
2011, Vol. 28 
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