Construction du barrage OA-11 sur la rivière Eastmain

Abstract

The OA-11 dam is the most important earth structure of the Eastmain – Opinaca – La Grande (EOL) project within the "La Grande" hydroelectric complex at James Bay, Quebec. Three rivers were diverted to the La Grande River to increase the hydroelectrical potential of LG-2 power plant. Dam OA-11, 33.2 m high, has a zoned section with an impervious central core. The soil conditions of the existing overburden along the 3214 m dam axis were very variable.The presence of pervious overburden at considerable depth along the dam axis makes it necessary to use an impervious cutoff under most of the length of the dam. On the right shore, a slurry trench was therefore built. It is 1.5 m wide, 2180 m long, and varying in depth from 3 to 22.7 m. In the river bed, the dam was built on an embankment pad of granular material pushed into the water and compacted by vibroflotation. A cast-in-place concrete wall was constructed to insure a cutoff through the pervious soils of the pad and foundation. This diaphragm wall is 595 m long, 0.6 m thick, and varying in depth from 2.6 to 35.7 m.This paper describes the different phases in dam construction with emphasis on techniques used for river closure. Key words: dam, compaction, construction, diversion, closure, cast-in-place concrete wall, river, slurry trench, vibroflotation.