Author
J. Ouellet, J. Hatley, S. Greensted, and M. Harper
Date
September 10, 2013
Publication
WTC 2013: World Tunnel Congress
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The authors completed a study for a new mine shaft in Saskatchewan’s Athabasca Basin where ground freezing is desired to reduce water inflows. Constraints were imposed on the design in terms of allowed water leakage (less than 10 m3/hour) inside the shaft. Since the shaft goes through highly permeable formations, water control measures were incorporated into the design. Ground freezing was selected as the most reliable and proven method for the sinking and a hydrostatic liner design was implemented. While exploring various technological options available for providing a fully hydrostatic liner, the authors came up with a new design concept that offers a more cost-effective solution while meeting all design constraints.

A new approach was developed for the membrane construction in order to resolve the issues created by the freezing conditions existing at the excavation walls. The membrane material requires a subgrade of shotcrete to smooth the irregular rock excavation surface. A working hypothesis was proposed by the lead author whereby the shotcrete base layer would serve to create a suitably smooth surface as well as provide a warm surface area for an extended period of time needed for spraying and curing of the three membrane coats.