超大平面沉井基础下沉施工全过程受力特性

Analysis on Mechanics of Super Large Plane Area Caisson Foundation in the Whole Process of Sinking Construction

研究目的:大型沉井基础具有整体性好、承载力强等优点,在桥梁基础中应用广泛。随着桥梁跨度的不断增加,沉井基础的面积也不断增大,给下沉施工中的沉井结构安全与施工控制带来越来越大的困难。本文针对连镇铁路五峰山长江大桥北锚碇超大平面面积沉井基础,对其下沉期间不同阶段施工工艺下沉井结构受力特性进行详细的计算与分析,从而为相应施工控制提供对策。研究结论:(1)随着沉井平面面积的增加,沉井结构在初期施工过程中受弯效应明显,变形量非常小;(2)传统的"大锅底"施工方法不再适合,而需要均匀开挖下沉及中部土体支撑;(3)沉井终沉前摩阻力增大会导致滞沉,空气幕及射水等措施能够有效助沉;(4)提出增加预应力钢束以增强抗裂性及异常工况抵御能力;(5)本研究结论可为类似超大平面沉井基础设计提供参考。

Research purposes： The large caisson foundation has the advantages of good integrity and strong bearing capacity,and is widely used in bridge foundation. With the increase of bridge span,the plane area of caisson foundation is increasing,which brings more and more difficulties to safety and construction control of structure in sinking. Aiming at the foundation of large plane area of the north Anchorage of Wufengshan Changjiang bridge in Lianyungang-Zhenjiang railway,this paper makes detailed calculation and analysis on the mechanical characteristics of sinking caisson structure in different stages,and suggests the corresponding construction control countermeasures.Research conclusions：（1） With the increase of the plane area of the open caisson,the bending effect is obvious and the deformation is very small in the initial construction process.（2） The traditional construction method is no longer suitable,but needs the uniform excavation sinking and the middle soil support.（3） The increase of frictional resistance before caisson sinking will result in hysteresis,air curtain and water injection can effectively help to sink.（4） It is proposed that the resistance to crack and abnormal working condition can be enhanced by adding prestressed steel.（5） The research results can provide reference for the desigh of similar caisson foundation.