Bridge main pier foundation double-layer steel sheet pile diaphragm wall combined cofferdam construction method

The invention discloses a bridge main pier foundation double-layer steel sheet pile diaphragm wall combined cofferdam construction method, and relates to the field of bridge main pier cofferdam construction, and the method comprises the following steps: S1, main pier cofferdam steel casings are inserted at intervals in the range of a rectangular cofferdam; s2, inner-layer steel sheet piles and outer-layer steel sheet piles are inserted and driven in a framing mode, the bottom ends of the inner-layer steel sheet piles and the bottom ends of the outer-layer steel sheet piles are inserted below a riverbed line, and the inner walls of the inner-layer steel sheet piles and the inner walls of the outer-layer steel sheet piles are both coated with waterproof soil layers; s3, an underwater diaphragm wall is constructed between the inner-layer steel sheet pile and the outer-layer steel sheet pile, and the upper portion of the underwater diaphragm wall and the lower portion of the steel sheet pile have a coincident sec