Authors: V. Bhardwaj, R. Halim, A. D. McAndrew, G. N. Cook, B.J. Osiowy
Canadian Dam Association Conference, Winnipeg, September 2008
Abstract
Cutoff walls are used to control seepage through dam foundations. A bentonite slurry trench cutoff wall, built in 1971, has successfully controlled seepage through a portion of the Butnau Dam at the Kettle Generating Station. This wall was 185 m long, 1.8 m wide, with a maximum depth of 18.6 m, and was the first of its kind built in Manitoba. Now almost forty years later, another slurry cutoff wall will be required below the Main Dam for the proposed 1485 MW hydroelectric development at the Conawapa Generating Station. The proposed cutoff wall at Conawapa is approximately 150 m long, 1 m wide, with a maximum depth of 35 m and is designed to block seepage through an alluvium filled deep trough below the dam’s foundation. It is designed utilizing advancements in both technical design tools and construction methodology that have become progressively available since the cutoff wall construction at the Butnau Dam.
The design is carried out using finite difference numerical analysis computer software Fast Lagrangian Analysis of Continua (FLAC). Using FLAC, the Main Dam, cutoff wall and its foundation were modelled to assess the long term performance characteristics. Various scenarios were modelled to determine the most suitable type of cutoff wall for the design. The final design will be integrated with Conawapa’s 3D geological and hydrogeological models. Knowledge and experience gained from the recent cutoff wall construction of the Shikwamkwa Dam in Northern Ontario, using specialized heavy equipment, is expected to be applied at Conawapa.
