Design of Artificial Island Cofferdam for East Anchorage of Shenzhong Bridge Based on Dynamic Increase of Silt Strength
The Shenzhong Bridge of Shenzhen-Zhongshan Link is a three-span steel box girder suspension bridge with a main span of 1 666 m.The east offshore gravity anchorage of the bridge is constructed by an artificial island cofferdam method.The cofferdam was preliminarily designed by a static method,to be a composite structure formed of interlocking steel pipe piles,I-type steel sheet piles and steel box hoops.To improve the material utilization rate,reduce the size of the cofferdam,and address the inconsistent stress among different constituents,the silt strength growth process was analyzed,and an artificial island cofferdam design based on dynamic growth of silt strength was proposed.The first parameters determined include the soil spring stiffness at the supports of the cofferdam as well as the equivalent elastic supporting stiffness of the parallel-steel-wire cable hoops at different construction stages.Subsequently,the response surface method is applied to establish the mapping relationship between different variables at different construction stages(including wall thickness and diameter of steel pipe piles and number of hoops)and control indicators(including maximum stress of steel pipe pile,maximum pile-top displacement and maximum stress of hoops).At last,the design parameters of the cofferdam are modified by the improved particle swarm optimization algorithm.By using the proposed dynamic design,a flexible composite artificial island cofferdam is determined,which consists of interlocking steel pipe piles(with a diameter of 2 000 mm and wall thickness of 18 mm)and I-type steel sheet piles and parallel-steel-wire cable hoops(seven cables,each consisting of 184,φ5 mm steel wires).The maximum stresses of the steel pipe piles in both the dynamic and static states were calculated by the finite element method and compared with the measured values.It is shown that the cofferdam designed by the dynamic method exhibits better load bearing capacity and more consistent stress among different constituents.
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