安庆长江铁路大桥3号墩巨型圆围堰气囊下河技术

安庆长江铁路大桥3号墩基础施工采用双壁钢围堰方案,围堰直径达56 m.为实现底节围堰下河,经方案比选,3号墩底节围堰高20.08 m,采用气囊法整体下河.通过在围堰内设置2道相互平行且与围堰井壁连接成整体的钢承重梁结构和底托架结构,作为气囊法整体下河上滑道.根据围堰结构并经计算,围堰滑道下方采用36只φ1.8 m×8.0 m规格的承托气囊.围堰下河场地选在下游一修船厂内,紧邻水边,尺寸约120 m×150m,入水口地面坡度为6.25％.入水口采取挖掘清淤方式形成水深3 m以上的陡坎,避免围堰入水搁浅.围堰下河后临时锚泊,以便完成落放托架和浮运编队工作.

Techniques of Air Bag Method Launching for Huge Circular Steel Cofferdam of Pier No.3 of Anqing Changjiang River Railway Bridge

The foundation of Pier No.3 of Anqing Changjiang River Railway Bridge was constructed by the circular double-wall steel cofferdam that is 56 m in diameter.To launch the bottom lift of the cofferdam,20.08 m in height,down to the river,the different construction schemes were compared and it was determined that the lift of the cofferdam would be integrally launched to the river by the air bag method.Before the cofferdam was launched,two steel load-carrying beams and base bracketing structures were set in the cofferdam,the beams were arranged in parallel with each other and were connected with the walls of the cofferdam and the beams and bracketing structures were used as the upper slipways for the launching.In accordance with the structural features of the cofferdam and the related calculation,36 nos.of the air bags,each in size of 1.8 m×8.0 m,were set underneath the slipways.The site for the launching was chosen at a place in the dockyard that has access road and power supply at the downstream of the river.The chosen site is close to the riverside,the area of the site is 120 m×150 m,the ground gradient at exit of the launching to the river is 6.25% and the exit was excavated into a sharp pit with water deeper than 3 m to avoid that the cofferdam would rush ashore.After the cofferdam was launched to the river,the cofferdam was temporarily moored to wait for the completing of setting of the brackets and floating formation of the cofferdam.