Abstract: The Second Stage Cofferdam is one of the most challenging structures in TGP (Three Gorges Project). Not only it is very important for TGP, but also very difficult. Some construction conditions did not appear before in cofferdam construction history. Researches were carried out during the whole process of construction of 18 years,and the construction was completed by using new theory, new technology and new materials. The cofferdam worked very well in its 4year operation. Even during its demolition, additional tests and data collection were specially arranged to explore some unclear points. Experiences of high cofferdam construction and research innovations were obtained and are applied to high cofferdam construction in west China. They will promote the water resource technology in China.

Key words: high cofferdam in deep water, flexible diaphragm wall, finite element analysis, centrifugal modelling, compound geomembrane, unsaturated and unstable seepage analysis