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TitleEvaluation of threshold freezing conditions for winter road construction over discontinuous permafrost peatlands, subarctic Canada
AuthorSladen, W E; Wolfe, S A; Morse, P D
SourceCold Regions Science and Technology vol. 170, 102930, 2019 p. 1-11,
Alt SeriesNatural Resources Canada, Contribution Series 20180329
Mediapaper; on-line; digital
File formatpdf; html
ProvinceNorthwest Territories; Nunavut
NTS85I/09; 85I/10; 85I/11; 85I/12; 85I/13; 85I/14; 85I/15; 85I/16; 85P/01; 85P/02; 85P/03; 85P/04; 85P/05; 85P/06; 85P/07; 85P/08
AreaTibbitt Lake; Cameron River; Gordon Lake; Tibbitt to Contwoyto Winter Road
Lat/Long WENS-114.0000 -112.0000 63.5000 62.5000
Subjectssurficial geology/geomorphology; geophysics; Nature and Environment; Science and Technology; Transport; permafrost; ground ice; periglacial features; organic deposits; peatlands; ice conditions; ice thickness; snow; floods; temperature; ground temperatures; logging techniques; thermal analyses; surface waters; lakes; Canadian Shield; road construction; road safety; air-freezing degree-day index
Illustrationslocation maps; tables; time series; profiles; plots
ProgramClimate Change Geoscience, Permafrost
Released2019 11 02
AbstractWinter roads provide an important transportation service in northern regions. The Tibbitt to Contwoyto Winter Road (TCWR), traversing subarctic Canada, is the busiest heavy-haul road in the world with as many as 10,900 truckloads per season. In addition to lake-ice thickness, trafficability on the TCWR depends upon adequate freezeback of overland portages, which are primarily peatlands underlain by discontinuous permafrost. We investigate threshold requirements for the initiation of winter road operations in this region and assess the use of a recommended 305 °C-day air-freezing index (FDD305a) value as an operational predictor of ground freezing at 30 cm depth, the desired depth to allow winter road construction to commence. Snow compaction and flooding were found to enhance freezeback of portages with early winter overland flow having a similar effect. The majority of winter road portages were not adequately frozen to a depth of 30 cm by FDD305a. Our results indicate that for drained and wet peatlands in this discontinuous permafrost environment, an FDDa threshold of 1100 °C-days is more appropriate than the 305 °C-day threshold. However, TCWR winter road operators presently plan the construction of the winter road by a calendar date rather than by evaluation of the air-freezing index. This practice results in a conservative approach to the start of the construction season, close to 1100 °C-days with a higher percentage of sites frozen to 30 cm depth than would be if the 305 °C-day air-freezing index was used as a guideline. In addition, the use of low-pressure vehicles for snow compaction during the start of the construction season is an effective adaptation practice to accelerate freezing penetration.
Summary(Plain Language Summary, not published)
Winter roads are seasonally constructed roads servicing remote communities and resource development sites in northern Canada. The lake ice and frozen ground provide stable surfaces for vehicular traffic that would otherwise not be possible. Guidelines require 30 cm of frozen ground to support heavy equipment and use 305 air freezing degree-days (FDD305a) as the threshold to start winter road construction over land. This paper investigates the ground thermal conditions at 30-cm depth in discontinuous permafrost peatlands on and off right-of-way along the Tibbitt to Contwoyto Winter Road (TCWR). During the study period, the FDD305a threshold was insufficient for frost penetration to 30-cm depth in wet peatlands typical of the subarctic Canadian Shield. The current calendar date threshold used by the TCWR does however, provide sufficient time for adequate frost penetration.