赤壁长江公路大桥南塔大型双壁钢套箱围堰施工技术

赤壁长江公路大桥主桥为(90+240+720+240+90)m双边箱钢-混结合梁斜拉桥,南桥塔墩位于长江深水区,基础采用先平台后围堰法施工。围堰为圆端形双壁钢套箱结构,长69.2 m、宽34.6 m、高27.0 m、重2755 t。针对渡汛工期紧张、下放精度高、安全风险高、封底质量控制难等一系列难题,通过采用围堰单元块制造,在墩位钻孔平台散拼,与桩基施工同步的技术,节省工期;采用接高护筒布置贝雷梁及分配梁,千斤顶多点吊挂下放,多点导向限位技术,以保证围堰下放精度;在吊挂自浮状态拼装接高第二节围堰,对称浇筑舱壁混凝土压重及对称吸泥下沉等技术,确保围堰施工安全;采用分区封底技术,保证了封底质量,顺利完成了围堰施工。

Construction Techniques for Double-Wall Steel Box Cofferdam of South Pylon of Chibi Changjiang River Highway Bridge

The main bridge of Chibi Changjiang River Highway Bridge is a cable-stayed bridge with span arrangement of 90,240,720,240 and 90 m.The superstructure consists of two latteral steel boxes,cross beams and concrete slabs.The south pylon is located in the deep water area of the Changjiang River.In the construction of the south pylon foundation,a working platform was built and a cofferdam was employed.The cofferdam,which is a double-wall steel box structure with round corners,measures 69.2 m(length)×34.6 m(width)×27.0 m(depth),weighing 2755 t.Facing challenges of flood threat,high lowering precision requirement,critical safety risk and demanding base-sealing quality control,it was decided that the cofferdam be manufactured in units,assembled on the platform at pier site,in tandem with the pile foundation construction to shorten construction time.The steel casings took form section by section,bailey trusses and spreaders were deployed,multiple jacks were arranged,and multi-point guiding and restricting technique was adopted to ensure the accurate lowering of the cofferdam.When the hanging system was in the self-floating state,the second lift of the cofferdam was installed.The bulkheads were concreted symmetrically for counterbalancing and muds were symmetrically dredged to assist the sinking of the cofferdam,so as to realize safe cofferdam construction.The base of the cofferdam was divided into different regions to ease the base sealing concreting and guarantee the base sealing quality.The cofferdam construction was successfully completed.