The Yangzizhou Ganjiang River Rail-cum-Road Bridge carries a portion of the Nanchang-Jiujiang High-speed Railway,the main bridge of which is a cable-stayed bridge with a main span of 320 m,two side spans of 144 m and two end spans of 48 m.The superstructure,featuring the ballast rail track,consists of steel trusses that act compositely with steel box beams that form the two levels of decks.The pylon piers,standing within the navigation channel where the riverbed overburden is shallow and the bedrock is hard,are supported on rectangular pile caps that are in turn supported by large-diameter bored piles and short rock-embedded piles.And an interlocking steel pipe pile cofferdam was used to facilitate the construction of the pile cap.The cofferdam of pylon pier G33 measures 54.56 m by 28.52 m,formed of interlocking steel pipe piles measured 28 m long and made from 1 020 mm-diameter auger pipes of Q355B steel.The steel pipe piles are connected with C-T clips.Inside the cofferdam,four layers of inner bracings are installed,each layer of bracings consists of three pairs of diagonals and inclined steel struts in the four corners.The bottom concrete bedding course contributes to load bearing capacity of the cofferdam.During the construction of the cofferdam,the XR360 drilling rig was used to drill holes in the bedrock,after the slurry was displaced with fine sands,the steel pipe piles were driven.The fine sands inside and outside the steel pipe pile were strengthened via high-pressure jet grouting.A smart monitoring system was developed to carry out real-time monitoring of the load bearing behavior and deformation of the cofferdam.The engineering practice proves that the cofferdam structure is safe,effective,easy to be constructed,and has better water retaining effect.
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