Recently, the innovative construction technology of a double-wall steel cofferdam on a floating platform, developed by China Railway 20th Bureau during the construction of the Yangjiawan Yellow River Grand Bridge at the Lanzhou hub of the Lanzhou-Chongqing Railway, won the third prize of the Gansu Provincial Science and Technology Progress Award.

　　The Yellow River Grand Bridge has a total length of 1,442 meters and 42 piers and abutments, including 4 piers in water. Depending on the underwater geological structure, different construction schemes were adopted, including steel boxed cofferdams, "island-building" cofferdams, and secant piles.

　　During construction, China Railway 20th Bureau innovated an assembled platform for double-wall steel cofferdam construction of in-water pier pile caps. The platform consists of multiple floating-body load-bearing steel beams erected on a horizontal load-bearing structure based on the principle of water buoyancy. The horizontal load-bearing structure includes two laterally arranged vessel floating bodies and two parallel longitudinally connecting steel beams. The vessel floating bodies are tightly connected as a whole through the two longitudinal connecting beams, and the multiple floating-body load-bearing beams are all arranged parallel to the longitudinal connecting beams. One to two vessel floating bodies and two longitudinal connecting beams form a rectangular frame-type load-bearing structure with a passage left in the middle for lowering the double-wall steel cofferdam, and the multiple floating-body load-bearing beams form a support platform for supporting the double-wall steel cofferdam. The vessel floating body is a floating support platform formed by connecting a vessel. Then, after underwater bottom sealing with concrete, drilling rigs are erected on the pile cap for drilling.

　　This technology features a simple structure, reasonable design, convenient erection and easy relocation, and flexible use. When lowering large-volume double-wall steel cofferdams, it overcomes shortcomings such as long construction periods, complicated procedures, large inputs of manpower and materials, high construction difficulty, and difficult control during the lowering process, thereby reducing project costs and improving economic benefits. (Huang Chaoquan)