Abstract:
This paper explores two recent case histories involving major rock excavation and hydro power engineering projects. The Mayo B hydro power project is located in the Yukon, Canada. An unstable, 25 m (80 foot) high rock slope, comprised of relatively weak, low-grade metamorphic bedrock, was remediated to mitigate risks to the intake structure below. The Pointe du Bois hydro power project is located in Manitoba, Canada. Extensive drill and blast bedrock excavation was necessary to construct new spillway approach and discharge channels, in granite to granodiorite bedrock. Trial drill and blast programs were conducted to optimize the methods for excavation, while adhering to strict roughness criteria required to satisfy the finished channel hydraulic design. The results and benefits of constructing these projects are briefly presented. Rock excavation and rock slope stabilization measures employed are described and illustrated by a series of figures and photographs.
Introduction
An existing intake, tunnel and powerhouse generating 5 megawatts (MW) of hydroelectric power, was constructed near Mayo, Yukon, in the 1950s. In 2010, the Owner, Yukon Energy Corporation, decided to proceed with the construction of the Mayo B project, involving construction of a new two-unit 10 MW powerhouse, a 300-m (985 foot) long intake tunnel, and 3.6 km (11,810 feet) of steel penstock. Completed in 2011, the project increased hydroelectric power generation capacity at this site from approximately 5 megawatts to 15 megawatts. The main benefits of the project include assisting with the saving of approximately $10 million (CDN) in annual diesel power generation, subsequently resulting in a reduction in greenhouse gas emissions of approximately 25,000 tonnes per year.
Manitoba Hydro undertook the construction of the new spillway at the Pointe du Bois project, involving deep excavations in hard granitic bedrock. The new spillway replaces approximately 100-year old facilities that consisted of 97 smaller sluiceway bays, all of which were manually operated. The new spillway structure includes a discharge channel that has a curved shape, with vertical bedrock walls. The walls measure 690 m (2265 feet) in length on the outer curve, and 430 m (1410 feet) on the inner curve. The maximum depth of spillway channel bedrock excavation is approximately 24 m (79 feet). The average width of the spillway channel is 120 m (395 feet). The bedrock excavation works were completed in 2014.
