Construction Techniques of Steel-Concrete Composite Cofferdam of Danjiangkou Reservoir Bridge
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.
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