La tranchée à boue lourde du barrage OA-11

Abstract

The OA-11 dam is the most important impounding structure of the Opinaca reservoir created by the water diversion of the Eastmain, Petit Opinaca and Opinaca rivers to the La Grande River to increase the hydroelectric potential of the LG-2 power plant. With a maximum height of 32.2 m and a crest length of 3214 m, this earthfill dam was built on relatively pervious fluvio-glacial deposits that made it necessary to use two impervious deep cutoffs (a slurry trench and a cast-in-place concrete panel wall). On the right shore, a slurry trench, 2180 m long, 1.5 m wide, and varying in depth from 3 to 22.7 m, was built.This paper describes the different construction phases of the slurry trench with emphasis on excavation and backfilling, and quality control. The slurry trench performance has been assessed in terms of the pore pressures developed in the foundation and at the toe during and after reservoir filling. Key words: dam, construction, cutoff, excavation, foundation, backfilling, soil–bentonite mixture, slurry trench, treatment.