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Keewatinohk Bipole III Converter Station

Keewatinohk Bipole III Converter Station
Date: 2015

The Keewatinohk Converter station is located in Northern Canada and, when completed, will help supply hydroelectric power to the province of Manitoba.
AGRA Foundations Limited was chosen to provide deep cast-in-place piles for building foundations in extremely difficult conditions including harsh climate, frozen ground, large cobbles and boulders, ice lenses and sub-surface water. Some of the piles were to extend up to 22 m below ground and required double casing, splicing of cages over the holes and the construction and installation of greases, poly wrapped sono-tube.


The overall stratigraphic condition of the site consists of peat and organic material overlaying a complex and varied intermediate soils unit, clay till and bedrock. Supplemental geotechnical investigations discovered deeper permafrost and frozen soils than originally assumed. The frozen soils and ice lenses discovered were observed at significant depths within the dense till layer at various locations. Significant amounts of ice were also observed in several building locations. The estimated depth of thaw sensitive soils at these locations is 15 m below final grade (top of granular pad).

Solution:

To resist the potential downdrag forces realized by 15 m of thaw sensitive soils, the piled foundations for each of these structures had to be installed below the depth of the thaw sensitive soils. The larger the diameter of the pile, the larger the potential downdrag load, and therefore the deeper the pile embedment below the thaw sensitive soils. A 600 mm diameter cast in place pile would need to be located approximately 20 - 22 m below ground. To do so, long, double casing had to be carefully installed without the aid of a crane, and greased, poly wrapped sono-tube had to be installed for each pile to further help reduce the frost heave.