武汉青山长江公路大桥南主墩锁口钢管桩围堰设计

Design of Locking Steel Pipe Pile Cofferdam for South Main Pier of Qingshan Changjiang River Highway Bridge in Wuhan

武汉青山长江公路大桥主桥为(350+938+350)m双塔双索面斜拉桥,大桥南主墩基础由大直径钻孔桩及哑铃形承台组成。承台平面尺寸巨大(98.9m×39.5m),埋置深度约15m,需进行超大型深基坑施工。承台采用锁口钢管桩围堰施工方案,围堰平面设计为101.7 m×41.3m的正多边形哑铃结构,总高35m,其中锁口钢管桩长33m,钢管桩顶部设有2m高单壁钢围堰(用以现场根据实时水位进行接高)。围堰共设有3层内支撑,内支撑为1.8m×1.2m的钢箱结构,封底混凝土厚5m,在承台系梁处设计8根1.8m辅助桩以减小封底混凝土应力。采用MIDAS软件对围堰整体及局部受力进行分析,结果表明,围堰结构各项指标均满足规范要求。

The main bridge of the Qingshan Changjiang River Highway Bridge in Wuhan is a cable-stayed bridge with double pylons,double cable planes and with span arrangement（350＋938＋350）m.The foundation for the south main pier of the bridge is comprised of the large diameter bored piles and the huge dimension dumbbell-shape pile cap.The plan dimensions of the pile cap are 98.9m×39.5m,the embedment depth is about 15 mand the construction of the pile cap in the very large and deep foundation pit is therefore needed.The pile cap is constructed,using the scheme of the locking steel pipe pile cofferdam.The cofferdam is designed as a regular polygon dumbbell-shape structure with its plan dimensions being 101.7m×41.3mand total height being35 m,of which the locking steel pipe piles are 33 mlong and on the tops of the steel pipe piles,the2 mhigh single-wall steel cofferdam（for the height extending of the cofferdam in the field according to the real time rising water levels）is arranged.Totally 3tiers of the internal bracings are arranged in the cofferdam,the internal bracings are the steel box structures in dimensions of 1.8m×1.2mand the base sealing concrete for the cofferdam is 5mthick.At the tie beams of the pile cap,8nos.of φ1.8mauxiliary piles are arranged in order to reduce the stress of the base sealing concrete.The software MIDAS Civil is used to analyze the global and local forces of the cofferdam and the results of the analysis demonstrate that the various indices of the cofferdam structure can meet the relevant requirements in the codes.