Innovative Repairs Restore Spillway Pier
The Slave Falls Generating Station is located on the Winnipeg River, about 35 km east of Lac du Bonnet, Manitoba. The generating station is more than 70 years old, making it one of Manitoba’s oldest power stations. The first unit went into service in 1931, three years after initial construction began on the $8.3 million-dollar facility. By the time construction was completed in 1948, eight vertical propeller type turbine generators were in service with a combined capacity of 68 MW. Today, the generating station has an average annual generation of 499 million kWh. The transmission lines provide 138 kV of energy to the City of Winnipeg in Southern Manitoba, Canada.
Problems that Prompted the Repair
After 87 years of use, the existing spillway was showing significant signs of age and demand for much-needed upgrades to maintain public safety, meet Canadian Dam Association (CDA) safety requirements and extend the service life of the structure.
The structure owners initially anticipated a Winter 2017 start date with repairs completed during Winter 2018. However, as more tests were performed by the rehabilitation project team it became evident that the structure required far more than planned traditional concrete repairs. Concrete core extraction and non-destructive testing by NDT Corporation (Sterling, Mass.) using their innovative impact echo/pulse velocity array revealed more significant deterioration than originally believed.
Working closely with Vector Construction Manitoba Division and the rest of the rehabilitation team, a new comprehensive repair plan was developed that would rehabilitate the pier and extend its service life by 20 years. A new cofferdam and scaffolding were placed to provide access to the structure. Polyurethane grout was injected into cracks in the existing concrete to limit water seepage. The damaged concrete was removed and a new containment wall was placed using high performance concrete.
To further complicate the project requirements, subfreezing temperatures required the piers to be heated and hoarded so that new critical path schedule with a March 31, 2018 deadline was successfully met.