Half a century of deep cutoff walls in Hydro-Québec dams and dykes

On a given river system, the first sites to be developed for dam construction are those with the best foundations. Eventually, the more difficult foundation conditions need to be tackled. Over the past 60 years, many deep to very deep cutoff walls have been constructed in the alluvium at several Hydro-Québec dams and dykes, including their cofferdams. Construction techniques, equipment capacities, quality control techniques, in-situ properties of the materials, and the general behaviour of the main retaining structures over the last 60 years are summarized together with thoughts on current research into improved materials.