The invention discloses a seaside ultra-deep soft foundation floating type steel
sheet pile cofferdam and a construction method thereof. The
cofferdam comprises two rows of steel
sheet pile walls, and the space between the two rows of steel
sheet pile walls is filled with backfill to form a wall-soil-wall dam body structure. A replacement sand layer is arranged on a foundation of the
cofferdam, and the two rows of steel sheet
pile walls penetrate through the replacement sand layer and are inserted in a mud layer side by side. The outer side of the steel sheet
pile walls is filled with a
riprap compressing body, and the
riprap compressing body and the replacement sand layer together form a soil and rock compressing structure. Horizontal steel sheet piles are arranged between the two rows of steel sheet
pile walls and perpendicular to the axial direction of the cofferdam. The cofferdam can float on the ultra-deep mud layer, the defect that in the prior art, steel sheet piles need to be inserted in a supporting layer to ensure stability is overcome, the cofferdam is not affected by the thickness of mud on the
surface layer of the foundation, and the application range is wide. The seaside ultra-deep soft foundation floating type steel sheet pile cofferdam is high in stability, short in construction cycle and low in
engineering manufacturing cost, construction quality is easily guaranteed and, the construction difficulty is low.