Authors: C.R. Donnelly, D.G. Protulipac, B.S.A. Tatone, Lassonde Institute, U of T, & C.Clark, Brookfield Renewable Power
Abstract
As a result of ongoing foundation seepage problems, a decision was made to replace the aging Shikwamkwa Dam located
near the town of Wawa in Northern Ontario. Construction of the new 35m high zoned embankment dam followed a
challenging fast-track design and construction approach with the dam completed in the fall of 2005, five months ahead of
schedule (Donnelly et al. 2007). This paper focuses on an evaluation of the hydraulic efficiency of the 21,000-square-metre
plastic concrete cut-off wall constructed beneath the new dam.
The hydraulic efficiency was analyzed with the aid of two-dimensional finite element seepage analyses based of
geotechnical models created based on the results of drilling investigations and laboratory permeability testing. The models
were calibrated by adjusting the geometry and hydraulic conductivity of the foundation materials (within the expected range
of uncertainty) such that the hydraulic head profiles obtained from the seepage analyses closely matched the measured
piezometric readings. Following calibration of the models, the hydraulic efficiency was calculated in terms of head
efficiency (Casagrande 1961) and flow efficiency (Terzaghi and Peck 1967). The new cut-off demonstrated a head
efficiency of 97.5% to 98% and a flow efficiency of 94% to 99.5% which are approximately 5% to 10% above the average
efficiency of fifteen similar concrete panel cut-off walls constructed elsewhere in the world, indicating that the new cut-off
wall meets and exceeds all of the design expectations.
