Scheme of pressure boost and floating aid for steel open caisson of main ship channel bridge of Hutong Changjiang River Bridge

The main ship channel bridge of the Hutong Changjiang River Bridge is a double-pylon continuous steel truss girder cable-stayed bridge with span arrangement (140+462+1092+462+140) m. The foundations for the main piers of the bridge are all the open caissons, of which the plan dimensions of the caisson top of the main pier No. 29 are 86.9 m×58.7 m and in the plan of the caisson, 24 well holes are arranged. The total height of the caisson of the pier is 115 m and the lower part of the caisson is the steel caisson that is 56 m in height. In the state of free floating, the draught of the steel caisson is 12.5 m, the caisson can not be floated out of the shipyard because of the deep draught and has the risk of grounding in the floating. To reduce the draught of the caisson and to keep the pressure in the air cabins of the caisson stable, the scheme of pressure boost and floating aid for the caisson was proposed, that was, 12 well holes in the caisson were symmetrically closed to make the well holes the sealed cabins. Meanwhile, the active pressure boost system was arranged and the air was injected into the cabins from the tops of the closing cover plates of the well holes. The pressure boost system was composed of the air compressor, main air pipes, branch air pipes, extension air pipes, air pressure meters, check valves, stop valves and liquid level sensors. By the measures of injecting the air for pressure boost and releasing the air for pressure reduction, the air pressure in each cabin was controlled. With the scheme of the pressure boost and floating aid, the steel open caisson of the pier was finally floated out from the shipyard to the pier site only in 3 h and the effect of the scheme implementation was sound. © 2015, Journal Press, China Railway Bridge Science. All right reserved.