HPP Glendoe - Rock Mechanical Aspects for Large Span Underground Powerhouse

The Glendoe scheme, presently under construction near Fort Augustus, near Inverness, by Scottish and Southern Energy (SSE), will be the first major conventional hydropower scheme to be constructed in the U.K. for the last fifty years and will generate up to 100 MW of electricity. The project will be the most efficient in the U.K. in terms of water to power production. The net head is 605 m, which is the highest head of any UK hydro scheme. The contractor executing the construction works, including the tunnels, underground powerhouse and dam, is the Hochtief Glendoe JV - led by Hochtief. Poyry Energy Ltd is the contractor's designer. Jacobs is advising the client.
After a short general description of the project, this contribution focuses on various rock mechanical design issues for the cavern powerhouse (PH). Located around 250 m below ground level it will incorporate a single 100 MW Pelton turbine. The size of the cavern excavated is (L x W x H) 47 m x 20 m x 33 m. Powerhouse and transformer caverns are designed as intersecting. Layout, shape and rock support were designed to optimize overall costs. Powerhouse detailed design commenced in June 2006, excavation commenced in January and finished in April 2007 ahead of schedule.