Seepage problems of deepwater high earth-rock cofferdam in Three Gorges Project

In order to compare the effect of different impervious scheme in the second phase cofferdams in the Three Gorges Project(TGP),the finite element method is employed to analyse three arrangement style:double concrete cofferdam,single low plastic concrete cofferdam combining with geomembrane inclined core and single-thick cofferdam.The 2D and 3D models are used to simulate seepage field of non-safety working station in stable and unstable cases,such as cracking in impervious elements,sudden drop of the water level.The numerical simulation gives out the contour lines of water potential energy in these cases.It shows that the double concrete cofferdam has better impervious effects than the other two schemes The cracking of the concrete cofferdam affects only on the down stream.From the unstable numerical analyses,the dropping depth of water level should be less than 2 meters per day in order to keep the safety of the cofferdam.