A Geotechnical Study of Glacially-Rafted, Weak, Clearwater Formation beneath a Tailings Dam, Fort McMurray Region, Alberta

This paper outlines an investigation into the distribution and geotechnical properties of glacial rafts derived from the detachment, transportation and emplacement of Clearwater Formation beneath a planned tailings dam in the Fort McMurray region, Alberta. The glacial rafts are weak clay-shales that typically display similar geotechnical properties and fabric to that of their parent material. The glacial rafts are shown to have low residual strengths and potential for a high pore pressure response that may influence the design and performance of the tailings dam.

The geology and hydrogeology of the tailings dam site are influenced by a buried, infilled, glacial channel called the Kearl Channel. The channel has eroded substantial portions of the Clearwater Formation and the underlying McMurray Formation and has influenced the deposition of glacial sediments in the northern part of the dam footprint. The Clearwater and McMurray Formations subcrop within the margins and to the south of the channel.

Geotechnical investigations and the inspection of excavation faces have identified glacially-displaced Clearwater Formation and associated Clearwater-derived till beneath the dam footprint. The diagnostic characteristics and typical geotechnical parameters for the rafts are presented with hypotheses for formation, transportation and deposition mechanisms. Uncertainty and the implications of the glacial rafts on the tailing dam design are addressed.

Bayliss, A.I., L. Philip, D. Hepp and S. Martens. 2013. “A Geotechnical Study of Glacially-Rafted, Weak, Clearwater Formation Beneath a Tailings Dam, Fort McMurray Region, Alberta,” in: Canadian Dam Association 2013 Annual Conference, Montreal, Quebec, October 5-10, 2013. Ottawa: Canadian Dam Association.

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