研究目的;在河床裸露、岩面坚硬不平整、深水的条件下桥梁承台多采用钢围堰、全封混凝土阻水进行施 工，当承台底与河床顶面高差较小不足于采用全封混凝土阻水时承台的施工就非常困难，本文研究上述条件 下承台的有效施工方法。
研究方法:以宜万铁路宜昌长江大桥m"墩承台施工为例，采用理论研究和工程实践相结合的方法，对该 桥11#墩承台施工方案、施工工艺、阻水结构的形式进行研究和力学分析。
研究结果:内腔封底双壁钢套箱围堰进行承台施工是一种新方法，在宜昌长江大桥11#墩承台施工中应 用取得了很好的效果。
研究结论:当承台底与河床顶面高差较小，不足以采用全封混凝土阻水时，采用环向封底的圆环形钢围堰 阻水结构施工承台是一种理想的选择。考虑到围堰的安装、下放等问题，采用长方形的内腔封底双壁钢套箱 围堰施工承台是一种不错的、较为实际的选择。
Research purposes ： The water-proofing method of full tremie seal is usually used in the construction of bridge pile cap under the condition of uncovered river bed, hard and inclined rock surface, deep water. But when the height between bottom of bridge pile cap and river bed surface is too little to do the full tremie seal, the construction will be difficult , This paper researches the efficient method under the conditions mentioned above.
Research methods：Take 11# pile cap of Yichang Yangtze River Bridge of Yichang-Wanzhou Railway Route for example, using the method of combining theory analysis and engineering construction, this paper studies the construction scheme , technics and the type of water-proofing structure.
Research results：The steel caisson cofferdam with double-shell and interspace tremie seal in construction of bridge foundation is a new and efficient method, which is used in the construction of 11} pile ,cap of Yichang Yangtze River Bridge and gets a very good effect.
Research conclusions：when the height between bottom of bridge pile cap and river bed surface is too little to do the full tremie seal, the circular cofferdam with ring tremie seal is an ideal method of water-proofing. But hen we take in account the problem of how to install and carry on under water the cofferdam, the quadrate steel caisson cofferdam with double-shell and interspace trimie seal will possibly be a good and practical method
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