嘉绍大桥主墩双壁钢围堰施工技术

嘉绍大桥主航道桥为六塔四索面钢箱梁斜拉桥,6个主墩承台均采用双壁钢围堰方案施工。钢围堰最大直径43.65m,内、外壁间距1.5m,高26m,以中心对称的方式布设8组组合导向定位装置(导向桩+滑动钢牛腿)。钢围堰在加工场内分片制作,在钢护筒与平台桩间搭设拼装平台,采用原位拼装工艺,利用龙门吊一次组拼成型;采用计算机同步控制下沉系统下放,辅以不均衡配载和"倒锅底形"吸泥工艺下沉到位。实践证明,该桥6个主墩钢围堰均顺利下沉到位,平面偏位50～90mm,垂直度小于1/400,均满足规范要求。

Construction Techniques of Double-Wall Steel Cofferdams for Main Piers of Jiashao Bridge

The main shipping channel bridge of the Jiashao Bridge is a steel box girder cable-stayed bridge with six pylons and four cable planes and the six pile caps of the main piers of the bridge were constructed by the double-wall steel cofferdams.The maximum diameter of the cofferdams is 43.65 m,the spacing distance between the inner and outer walls of a cofferdam is 1.5 m,the height of the cofferdam is 26 m and additionally a cofferdam was also provided with eight groups of the combined guiding and positioning devices(guiding piles+sliding steel brackets) arranged in a center-to-center symmetric way.All cofferdams were manufactured piece by piece in the workshop and at a pier site,the assembling platform for the cofferdam was set up in between the steel casings and platform piles and the cofferdam was well assembled in one time by the gantry carne,using the pier site assembling construction technology.The cofferdam was then lowered down by the sinking system synchronously controlled by computer and was sunk down in place by the aid of the unbalanced ballast and the "inverse pan" dredging.Practice proves that the six cofferdams for the main piers of the bridge have been finally smoothly sunk down in place.The plan deviations of the cofferdams are 50～90 mm and the perpendicularity is less than 1/400,which all satisfy the relevant requirements in the codes.