Abstract: The side of a hydraulic structure in contact with the water is covered with an impermeable membrane consisting of series of plastics so-called GEOSELLS which feature scales. These are interlocked with each other and then welded together edge to edge, and fixed to the structure by vertical fixings allowing movement of the GEOSELLS. This also favors drainage and initiation of microfissures regularly distributed in the structure. A granular coating is applied to the external surface at a raised temperature. This method is particularly suited to sealing granular rubble structures with or without binder. In rigid structures the binder may be a cement or a cement derivative, possibly a resin ("roller compacted concrete"). In flexible structures the binder may be a resin or a textile with or without reinforcing elements.