High flow plastic soft land construction difficulties, the use of steel sheet pile cofferdam cofferdam is ideal, steel sheet pile, especially the locking steel plate pile, can effectively block the high flow plastic silt to pit Chung soil, and can effectively form a waterproof curtain, can effectively overcome the supporting method in slope Chung soil crashed ills. For example, the thickness of soft soil in some area is mostly 3~8m, and the following is hard soil. 8~10m long steel sheet pile can be inserted into hard soil, which can overcome the problem of foundation pit uplift and do not have to worry about the side slope of pile bottom in soft soil. Steel plate pile with braces, anchor (or horizontal brace) can effectively control the slope lateral displacement, and the construction period is shortened. The foundation pit support is a temporary project, and the steel sheet pile can be recovered. At present, the construction of the steel sheet pile is generally used, so the cost is not high. In short, the steel sheet pile support scheme has the advantages of safety and reliability, fast construction and cost saving, especially for the high flow plastic soft soil foundation pit enclosure in Ningbo area.