宁安铁路安庆长江大桥主塔墩深水基础施工技术

摘要

为实现汛期安全、优质、快速地进行近40 m水深、大流速条件下的每墩37根嵌泥岩97 m的φ3.4 m/3.0 m变径钻孔桩,直径51m、厚8m承台的深水基础施工.宁安铁路安庆长江大桥两主塔墩基础均设计采用外径56 m、壁厚2m,高分别为42.88 m和41.4m的无支撑圆形双壁钢套箱围堰结构进行施工,实现了围堰平台一体化.获得了深水无支撑巨型圆形双壁钢套箱围堰的设计和施工,无导向船的前后定位船锚碇系统实现围堰的精确定位、无覆盖层不平岩面围堰底口处理、钻孔桩护筒底口流砂和坍塌问题的解决、大直径变径钻孔桩清水法钻孔、31m高落差大体积混凝土灌注等关键技术成功应用的经验.%This paper introduces the successful construction experiences of the foundations of two main pylon piers of Anqing Yangtze River Bridge in Nanjing-Anqing Railway under the conditions of 40 m deep water and torrential water flow during flood season. Every foundation is made of 37 drilled piles embedded into mudstone 97 m deep with 3. 4 m/3. 0 m variable diameters, and every pile cap is 8m thick with 51m diameter. The foundation is constructed within supportless double-wall steel-boxed cofferdam with 56m outer diameter, 2 m wall thickness, 42. 88 m and 41. 4 m height respectively, so as to form the integration of the cofferdam and platform. Then, the successful experiences of several key techniques are summarized for the construction of supportless double-wall steel-boxed cofferdam in deep water, such as the accurate positioning of cofferdam by anchor system without guide ship, the treatment of cofferdam bottom, the resolving of quicksand and collapse at pile-casing bottom, the drilling method with clear water for drilling pipe of lager and variable diameter, and the concreting method of mass concrete with 31 m altitude difference.