平潭海峡公铁两用大桥鼓屿门航道桥主墩基础设计

Design of Main Pier Foundations for Guyumen Channel Bridge of Pingtan Strait Rail-cum-Road Bridge

平潭海峡公铁两用大桥鼓屿门航道桥采用主跨364m的钢桁混合梁斜拉桥方案,桥址区水深流急、风大涌险、潮大浪高、地质复杂、冲刷严重、航道等级高、有效作业时间短。为适应该桥桥址气象、水文、地质等条件,考虑通航安全、技术可行及工程经济性等要求,确定采用高桩承台方案,并对3.0m、4.0m、4.5m钻孔桩基础方案进行比选,确定选用4.5m钻孔桩基础方案,按先平台后吊箱围堰的顺序施工。大直径桩基础中各桩采用单独配筋设计;防撞结构由吊箱围堰、V形防撞梁及联结系组成,采用可拆卸式设计,并在围堰外壁设置消波孔;钻孔桩采用KTY5000型动力头钻机,并配制PESF935型中压空压机循环排渣,利用泥浆护壁、锲齿或球齿滚刀钻头钻具切削岩面成孔;采用内径406mm的单导管法施工水下C45混凝土。

The Guyumen Channel Bridge of the Pingtan Strait Rail-cum-Road Bridge adopts the scheme of a steel truss hybrid girder cable-stayed bridge with a main span of 364 m.The construction of the bridge is constrained by the complex geological and hydrological conditions at the bridge site,including deep water,strong currents,heavy winds,hazardous torrents,high tides and turbulent waves,severe scour,high grade of navigational channel and tight efficient operation time.To suit the meteorological,hydrological and geological conditions at the bridge site,by considering the safety and technical feasibility and engineering economy,it was determined that the elevated pile cap scheme be adopted.The pile foundations formed of bored piles respectively with 3.0m,4.0mand 4.5mdiameters were compared,and the foundation scheme of 4.5mdiameter bored piles was finally chosen.The foundation was constructed following the sequence of constructing the platform first and then the suspended box cofferdam.For the foundations of large diameter bored piles,each pile has its own reinforcement design.The collision protection structure was formed of the suspended box cofferdam,V-shaped collision protection beams and lateral bracings,which are able to be dismantled,and wave absorbing holes were drilled on the outer wall of the cofferdam.The bored piles were drilled by the KTY5000 driller and the PESF935 medium and vacant pressure machine for circular dredging.The hole took form by using the slurry wall protection and the gear-tooth or ball end hob cutter to cut the surfaces of the rocks.The C45 tremie concrete was cast by single conduits with an inner diameter of 406 mm.