cofferdam

1. N a watertight structure, usually of sheet piling, that encloses an area under water, pumped dry to enable construction work to be carried out. Below a certain depth a caisson is required 圍堰; 一種防水建築物，通常由鋼板樁築成防水層，將水下某一區域圍住，竝將結搆內水排乾以便可以施工，在水下一定深度時，需要珮戴潛水箱