Construction of the Bennett hydro development

Abstract

The Bennett dam forms a reservoir with a volume of 71 km 3, of which the useful storage is 37.5 kin3," the length of the reservoir is 360 kin, and the surface area is 14,000 km 2. The dam is located in a canyon whose flanks and base are composed of sedimentary rocks, intercalating beds of sandstones and shales with interlayers of coal up to 1 m thick. The bedrocks are covered by lacustrine deposits containing clay and sand. Construction of the hydro development began in the fall of 1961 by decision of the government o f the province of British Columbia.The temporary residential village, subsidiary enterprises, a small air field, and roads within the construction area were built in 1962-1963, and the access road, about 85 km long, connecting the construction site with the railroad, was reconstructed. At this time three diversion tunnels, each 760 m long and 14.4 m in diameter with a concrete lining, were driven in the right bank. In September 1963 the river was dammed, after which construction of the 36-m-high earth cofferdam and preparation of the dam foundation began. The loose deposits and weathered rock were removed, with the exception of the foundation of the upstream cofferdam, which became a part of the upstream shoulder of the dam.To prevent subsequent differential settlement of the dam, the step slopes of the canyon flanks were flattened to 1: 1, the considerable depressions in the core abutment zone were filled with concrete, and all roughnesses on the flanks were gunited. Under the entire core of the dam the rock was grouted to a depth of 18 m. A grout curtain up to 20 m wide and up to 105 m deep was made along the entire dam front.