Structural Design and Construction of Steel Cofferdams for Pile Caps of Pylon Piers of Jiashao Bridge

The main bridge of the Jiashao Bridge is a cable-stayed bridge having the single pile single column piers,six pylons and four cable planes.The pile cap of pylon pier of the bridge is a circular shape and deeply buried structure that is constructed by way of integrally lowering a cofferdam without bottom.The cofferdam is made up of the lateral wall system,guiding system,internal bracing system and lowering system.The techniques for construction of the cofferdam are summarized herewith from aspects of setting-up of the assembling platform,assembling of the lateral walls,installation of the guiding system and positioning system,arrangement of the lowering system,casting of concrete into the cutting edges and sinking of the cofferdam.The cofferdam is sunk down in four stages of sinking by the self weight of the cofferdam,sinking by water pumped into the cofferdam,casting of concrete into the bulks of the cofferdam,sinking by mud air-lifting and the final time casting of concrete into the bulks and sinking by air-lifting.Practice proves that the construction of the cofferdams of the bridge is quite successful,the vertical and plan position deviations of the cofferdams can all satisfy the relevant requirements in the technical specification.