Secondary bottom sealing cofferdam

The utility model discloses a secondary bottom sealing cofferdam, which comprises a cofferdam lateral die, a ring beam and an inner support; and the bottom sealing concrete at the bottom of the cofferdam is composed of lower-layer water sealed concrete and an upper-layer dry sealed concrete. The cohesive force between the water sealed concrete and a steel casing is smaller, while the cohesive force between the dry sealed concrete and the steel casing is greater, thereby enhancing the security of the system. Due to application of the secondary bottom sealing cofferdam, the thickness and the amount of the bottom sealing concrete can be greatly reduced, the total height of the design of the cofferdam is further lowered, and with regard to a suspension box-cofferdam, the requirements of strength and rigidity of a bottom die bracket and a bottom die are also lowered. The cofferdam is suitable for larger buildings and construction of underwater buildings with lower water level or frequently-variable water level.