Deep and thick silt geological cofferdam bottom sealing construction method

The invention discloses a bottom sealing construction method for a cofferdam in the deep and thick silt geology, and solves the problem that the bottom sealing bearing capacity of a deep and thick silt layer is insufficient through successful application of the bottom sealing construction method for the cofferdam in the deep and thick silt geology. According to a previous method, an original foundation surface serves as a bottom elevation reference surface of bottom sealing concrete, the anti-floating and anti-sinking requirements of the concrete are met by increasing the binding power of the concrete, a steel sheet pile cofferdam and a steel pile casing, and the problems that if large-area concrete is adopted, the concrete is increased, and the safety performance of subsequent construction is low are solved. On the original basis, it is ensured that no sludge is deposited on the base face of the bottom sealing base through further sludge suction and dredging, and strength reduction caused by mixing of bottom