Excavation of World’s Largest Underground Powerhouse

The LG-2 site is located in the nordic region of northwestern Quebec and is the principal installation of the La Grande River hydroelectric power development. As such, it presents formidable problems in organization, logistics, contract administration, and construction techniques. The powerhouse contains 16 generating units; each of 333 mw and required 3,650,000 cu yd (2,792,000 m3) of rock excavation. The rock is granitic gneiss typical of the Canadian shield region and is of exceptionally good quality. Rock support is entirely by rock bolts with shotcrete used locally. Roof arch deformation is minimal. Considerable specialized excavation equipment was used. Rock pillars at the intake and rock ledges to support the main overhead cranes in the powerhouse complex were successfully carved by controlled blasting. Economies in excavation were achieved by relying on field control by a geotechnical team rather than design conservation.