丹江口水库特大桥钢-混凝土组合围堰施工技术

Construction Techniques of Steel-Concrete Composite Cofferdamof Danjiangkou Reservoir Bridge

丹江口水库特大桥为主跨760 m双塔双索面部分地锚式混合梁斜拉桥,主墩采用整体式承台+大直径群桩基础,主墩承台平面为八边形,尺寸为48 m(横桥向)×26 m(顺桥向)×6.5 m(高),承台底部设置26根直径2.8 m钻孔灌注桩。为适应库区倾斜裸岩地形,降低施工难度及施工费用,主墩围堰采用下部混凝土挡墙围堰+上部单壁钢围堰的钢-混凝土组合围堰方案。下部混凝土挡墙围堰采用衡重式挡墙围堰及抗滑桩挡墙围堰,高3~11 m;上部单壁钢围堰分块设置,其长度与下部挡墙围堰匹配,高8 m。钢-混凝土组合围堰施工时,首先根据地形条件进行挡墙围堰分段,之后采用破碎锤开挖混凝土挡墙围堰基础;混凝土挡墙围堰采用分层、分块施工,顶部圈梁与挡墙围堰同步浇筑;上部单壁钢围堰采用加工厂预制+现场分块安装,并预留竖向型钢接长部分;最后进行单壁钢围堰底部及组合围堰山体连接处止水混凝土施工,完成钢-混凝土组合围堰施工。钢-混凝土组合围堰的应用,有效缩短了基础施工周期,降低了围堰施工难度及施工费用,经济合理,满足现场施工各项要求。

The Danjiangkou Reservoir Bridge is a two-pylon,partially-earth-anchored,hybrid girder cable-stayed bridge with a main span of 760 m.The stay cables are arranged in double cable planes.Supported by 26 bored piles of 2.8 m diameter,the integral octagonal pile caps of pylon piers measure 48 m(along bridge width)by 26 m(along bridge length)by 6.5 m(depth).A type of steel-concrete composite cofferdam,which consists of the lower concrete retaining walls and the upper single-wall steel cofferdam,is applied to accommodate the slant bare rock terrain in the reservoir region,and to reduce construction challenges and costs as well.The lower concrete retaining walls incorporate the counterweight retaining walls and the walls of anti-slip piles,measuring 3 to 11 m deep,while the upper single-wall steel cofferdam,assembled from prefabricated constituents,matches the upper cofferdam in length,with a depth of 8 m.During construction,the retaining walls were divided into multiple zones to suit the geological conditions,crushing hammers were used in cofferdam pit excavation,and the concrete retaining walls were constructed in layers and zone by zone,cast parallel with the top collar-tie beams.The upper single-wall steel cofferdam was prefabricated into segments in the factory and transported to the bridge site for assembly,with the vertical rolled sections reserved for further elongation.The utilization of the steel-concrete composite cofferdam effectively shortened the construction schedule of the foundation,reduced the construction challenges and costs,which was proved an economic option that suited the site environments.