An aging dam structure located in Mission, British Columbia, Canada was in need of upgrades and reinforcement to prevent a critical failure in the event of an earthquake. In addition, equipment in the dam’s powerhouse—built in the 1930s—was obsolete and could not provide the required amount of output, so it needed to be replaced.
The Ruskin Dam is a 110-meter-long (360.9-foot) and 59-meter-tall (193.6-foot) concrete gravity type. The dam creates a reservoir (Hayward Lake) with a 42,000,000 cubic meter (34,050 acre-foot) capacity and its spillway is an ogee-type that consists of seven radial gates. The dam's powerhouse is immediately adjacent on the river's eastern bank and contains three 35-megawatt turbine-generators.
West Coast Cutting & Coring Group Ltd. was awarded the demolition contract. The concrete sawing and drilling work involved the cutting and removal of four existing piers, the bridge deck and sections of the spillway. Other tasks included cutting free old generators, intakes, gate slots, draft tubes and creating new steps on the spillway for new pier forms. In addition, deep hole drilling was specified for the installation of seismic anchoring and the spillway surface required scarifying for reinstatement.
There were a number of factors complicating this job, both from an environmental aspect and in terms of specifications. A large portion of the work was done on the face of the dam spillway, which was on a 60-degree slope with limited access. In addition, it was specified that there be a 1-inch tolerance for the form work. Compounding the level of difficulty of the project, the reservoir below the work area contained salmon that were spawning, so protection of this wildlife and water within the reservoir had to be considered when planning the work.
20 million pounds of concrete was saw cut and removed above and below water, 5,000 holes cored to depths of up to 12 meters (39.4 feet), 697 square meters (approximately 7,500 square feet) of surface scarified—completed in phases over a three-year period.
West Coast Cutting & Coring Group Ltd. successfully completed the project ahead of schedule and with zero lost time injuries.