Construction of Double-Wall Steel Suspension Cofferdams for Jiashao Bridge

The north auxiliary shipping channel bridge of the Jiashao Bridge is a 4-span continuous rigid-frame bridge employing group bored pile and pile cap foundations.In the light of the special hydrologic and geologic conditions of the Qiantangjiang River at the bridge site,the double-wall steel suspension cofferdams are used as the water retaining structures that at the same serve as the formwork for the pile caps in the construction of the foundations.A cofferdams is fabricated in sections and is assembled into an integrity in field.The cofferdam is then lowered to the designed elevation by 4 sets of 100-t hydraulic jacks.After the cofferdam is set in place,the cofferdam base is sealed by tremie concrete and the water inside the cofferdam is pumped out.To ensure the safety of lowering of the cofferdam and casting of the tremie concrete under strong tide and scouring,the transverse stability of the cofferdam is reinforced by installing 2 levels of guiding devices on the side plates and 8 strut bolts on the bottom plate.At present,the base sealing of 8 cofferdams has been completed and the construction of pile caps has been carried out.The deviations of the plan positions of the assembled and lowered cofferdams can comply with the relevant requirements in the technical specification.The base sealing of a cofferdam is successfully completed in one time and no water leakage problem has been found.