Special repairs to the Bersimis-1 generating tunnel walls to increase power production: a case study

• Published in: Canadian journal of civil engineering Vol. 28; no. 3; pp. 411 - 418
• Main Authors: Mirza, J, Mirza, M S, Roy, V, Lemire, C, Saleh, K, Tremblay, S
• Format: Journal Article
• Language: English
• Published: Ottawa, Canada NRC Research Press 01.06.2001; National Research Council of Canada; Canadian Science Publishing NRC Research Press
• Subjects: Applied sciences; Buildings. Public works; Dams and subsidiary installations; Durability. Pathology. Repairing. Maintenance; Electric power plants; Environmental aspects; Exact sciences and technology; Hydraulic constructions; Protective coatings; Repair (reinforcement, strenthening); Tunnels; Tunnels, galleries; Canada; Quebec Canada; Surface cleaning; Hydroelectric power plant; Headwater tunnel; Construction parameter; Plugging; Inspection; Material selection; Slime; Finite element method; Abrasion resistance; Concrete construction; Numerical simulation; Economic aspect; Rehabilitation; Protective coatings
• ISSN: 0315-1468; 1208-6029
• DOI: 10.1139/l01-005

The intake concrete tunnel at Bersimis-1 generating station is coated with a black sticky substance (slime) approximately 5 mm in thickness. Since the tunnel is 12 km long and has an average internal diameter of 9.45 m, the deposit represents a considerable obstacle to the production of electric power. The resulting loss of power generated is estimated to be around 39 MW per year, valued at 71 million dollars. Inspections in 1979, 1981, and 1983 showed that simply cleaning the surfaces would reduce the power losses but the slime built up again after a few years. A thin, smooth protective coating, containing anti-slime agents, compatible with the existing concrete could protect the surfaces against erosion and limit the slime deposit and its harmful effect on power production. The 1993 inspection provided an opportunity both to analyze the concrete, the slime itself, and the water and to experiment with the various methods of cleaning the surface and applying the different coating products. In 1994, 11 other products were selected for the specified characteristics and applied on concrete pipes and installed at two different locations: one consisted of submerged concrete specimens in the Bersimis river and in the second test setup, the products were installed by creating an artificial environment similar to the tunnel conditions using the tunnel water. The results showed that some products do not resist these conditions. Abrasion resistance tests in the laboratory confirmed these observations. One of the eleven products, a polymer-modified cement-based mortar, passed the submersion test and was applied to a small surface area (125 m 2 ) of the tunnel during a generating station shutdown in 1995. The thickness of the mortar required to cover the walls of the tunnel was between 2 and 3 mm. The total cost of repairing with the mortar was estimated to be between 10 and 11 million dollars. The size of the tunnel, its restricted accessibility, cleaning, ecological disposal of the slime, and the large quantities of material to be applied to cover the entire tunnel added to the complexity of the project.Key words: intake tunnel, power production, protective coating, slime deposit, surface cleaning.