黄冈公铁两用长江大桥主墩基础围堰施工技术

黄冈公铁两用长江大桥主桥为双塔双索面钢桁梁斜拉桥,主墩基础采用双壁钢吊箱围堰法施工。钢吊箱围堰在岸上整体拼装制造,通过测量控制围堰的轮廓尺寸,桩位,上、下导环的位置与同心度等,确保基础施工后主墩钻孔桩及承台施工偏差符合标准要求,并根据实测结果综合分析得出钢围堰的定位精度;采用气囊法下水,将下水坡度从1∶30逐渐调整为1∶5,保证了围堰入水速度及入水滑移距离;利用大马力拖轮设备组合将围堰整体浮运至墩位;利用重力锚碇加定位船系统分初定位、精定位和体系转换3个阶段进行围堰定位,其平面定位精度在5cm内,钢吊箱垂直度在1/1 000内,钢护筒垂直度在1/500内,均满足标准要求。

Construction Techniques of Cofferdams for Main Pier Foundations of Huanggang Changjiang River Rail-cum-Road Bridge

The main bridge of Huanggang Changjiang River Rail-cum-Road Bridge is a steel truss girder cable-stayed bridge with double pylons and double cable planes and the foundations for the main piers of the bridge were constructed by the double-wall steel boxed cofferdams.The cofferdams were integrally manufactured and assembled on bank and by means of survey,the overall dimensions,pile locations and the locations and concentricity of the upper and lower guiding rings of the cofferdams were controlled in order to ensure that the deviations of the bored piles and pile caps of the main piers could comply with the relevant requirements in the standards after construction and to obtain the accuracy of positioning of the cofferdams according to the results of comprehensive analysis of the survey.The cofferdams were launched to the river by air bags by way of gradually adjusting the launching gradient from 1∶30 to 1∶5 so as to ensure the launching speed and sliding distances of the cofferdams.After the cofferdams were launched to the river,they were floated to the pier sites,tugged by the strong house power tug boats and were positioned by the gravity anchors plus positioning barges in three stages of initially positioning,accurately positioning and system transformation.The final accuracy of positioning of the cofferdams in plan is 5 cm,the perpendicularity is within 1/1 000 and the perpendicularity of the steel casings is within 1/500,which all meet the requirements in the standards.