哑铃形超大钢吊箱气囊法下水施工技术

Construction Techniques for Launching Very Huge DumbbellShape Steel Boxed Cofferdam by Air Bag Method

九江长江公路大桥主桥为双塔混合梁斜拉桥,22号墩哑铃形承台采用超大钢吊箱施工,钢吊箱采用气囊法下水。施工时采用1.5m、1.8m规格的气囊,设置了牵引与止速设备、下水后的稳定装置及脱缆设备。经钢吊箱下水工况分析可知:气囊布置合理,气囊承载力及钢吊箱下滑力均满足要求,钢吊箱最终吃水深度4.65m。钢吊箱下水施工时,按间距4m左右布置气囊,对气囊充气后进行松墩、撤墩,启动绞车使箱体向下滑移直至自滑(滑移中采取充、放气的方法调整气囊间距),解除底托板,进行脱扣作业,使钢吊箱快速下水自浮。该桥钢吊箱气囊法下水施工顺利,入水状态及最终吃水深度均与设计相符。

The main bridge of Jiujiang Changjiang River Highway Bridge is a hybrid girder cable-stayed bridge with double pylons and the dumbbell-shape pile cap of Pier No. 22 of the bridge was constructed by the very huge steel boxed cofferdam that was launched to the river by the air bag method. In the process of launching the cofferdam, the air bags of Ф1.5 m, Ф1.8 m were used and the hauling, speed control equipment, the stability device and cable disconnecting equipment for the cofferdam in the river were provided. It was known from the analysis of launching load cases that the layout of the air bags was rational, the bearing capacity of the bags and the sliding forces of the cofferdam could meet the requirements and the final draught of the cofferdam was 4. 65 m. The air bags for the launching were laid out at a spacing of about 4 m and after the bags were filled with air, the cofferdam was released and removed from the temporary supports and the winch started to make the cofferdam slide downward until it would slide by itself （the spacing of the air bags in the launching could be adjusted by filling and releasing air in the bags）. The base plates under the cofferdam were then released and the cofferdam was disconnected to make the cofferdam slide quickly downward the river and float there. With the air bag method as described, the launching of the cofferdam proceeded smoothly and the status and draught of the cofferdam in the river were accordant with those of the design.