2022 – Recent case histories of underwater rehabilitation with geomembranes: in still water and in flowing water

Gabriella Vaschetti, Alberto Scuero, John Cowland – Carpi Tech Carpi Tech, Carpi Asia Pacific

For a safe and sustainable future, dams and related hydraulic structures need maintenance. Preventing, stopping, or minimising seepage is one essential aspect for the safety and the efficiency of dams, reservoirs, canals, hydro tunnels, and shafts. At the beginning of the 1990’s the Carpi geomembrane technologies already adopted for two decades in all types of hydraulic structures were subjected to intensive in-house research and joint research with independent entities, with the aim of developing systems that could be installed underwater on the upstream face of leaking dams and hydraulic structures in general. The underwater geomembrane technologies thus developed started being adopted on a full scale in 1997 and have been used ever since to repair the full face of dams, or specific leaking areas, or failing joints. As underwater installation expertise in still water increased, based on its 40 years of experience in lining canals with geomembranes, Carpi explored the possibility of extending the underwater geomembrane technology to canals, which often cannot be dewatered, or can be dewatered only at great inconvenience and high cost. Studies and research led to the creation of SIBELONMAT®, a geomembrane system that can be installed in flowing water, avoiding outage of the canal. SIBELONMAT® is a mattress formed by two watertight geomembranes, prefabricated in a factory, and then deployed underwater on site, to line the entire cross section of the canal or only parts of it, and joined underwater to the adjacent SIBELONMAT® mattresses by a patented system with heavy duty watertight zips. The mattresses are then filled with cement grout providing the permanent ballast and anchorage for the bottom geomembrane that provides watertightness, while the top geomembrane confines the grout. SIBELONMAT® has been installed in three pilot projects, the most recent of which with an improved version incorporating a monitoring and leak location system. This paper addresses objectives, design, characteristics, and installation aspects, by presenting the two most recent underwater projects: in still water, at Studena, a 55 m high buttress dam in Bulgaria, and in flowing water at Kembs embankment, which is part of the Grand Canal d’Alsace, a navigation canal in France. Some information on further development that is being carried out to transform the SIBELONMAT® to reduce underwater works costs is also presented.