宁安铁路安庆长江大桥主塔墩深水基础施工技术

Construction Technology of Foundation with Deep Water of Main Pylon Pier of Anqing Yangtze River Bridge in Nanjing-Anqing Railway

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3.4 m/3.0 m变径钻孔桩,直径51 m、厚8 m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2 m,高分别为42.88 m和41.4 m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、31 m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 51 m 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.