Geomechanical Properties of Muskeg (Peat)

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Canada has more muskeg (peat) covered land than any other country in the world, covering 18% of the land area, primarily in northern areas of the country. The common view of muskeg in geotechnical engineering is that it should be avoided as a foundation material whenever possible. However, avoidance is not always an option, particularly for linear, continuous structures such as those required for roads, railways and pipelines. As resource and infrastructure development continues to expand, particularly in northern Canada, it is anticipated that the number of engineering projects involving peat will only increase. In northern Alberta, older infrastructure constructed over muskeg has been subjected to large increases in traffic over the past decade, and this has resulted in widespread and ongoing stability and settlement issues. Muskeg forms by the process of terrestrialization. This process starts at the margins of a shallow body of water, and due to the acidity, anoxic conditions and temperature of the water, the decay of the plant material is slowed to a pace at which it begins to accumulate and fill in the lake. This results in a range of peat formations, depending on the type of accumulated plant material, the state of decay and the access to oxygen. Muskeg has been described as an “ordinary extraordinary material” (Hobbs 1986). This highlights the fact that peat exhibits similar traits and correlations between geotechnical engineering properties and classification properties as mineral (particulate) soils (and thus ordinary); but with values for these properties that are greatly different from mineral soils (thus extraordinary). One example of this is the strength of peat, which is remarkably high given its exceptionally high water content. Muskeg also demonstrates a high degree of variability spatially as well as between different formations within a single region. Due to its complex nature, muskeg foundations pose unique problems for construction and maintenance of infrastructure constructed on top of it. Several important gaps in the understanding of the fundamental engineering properties of muskeg were identified during previous and current research conducted by the applicant. These gaps include 1) a quantification of the variability of muskeg properties, and the effect of this on the selection of muskeg properties for the construction and remediation of infrastructure; 2) a model for the time-dependent deformation behaviour of muskeg under embankment loading which results in the large settlements; and 3) a complete characterization of the anisotropic strength and stiffness properties of muskeg which are fundamental to the determination of the stability of muskeg foundations. The results of this research are expected to contribute to the safety and reliability of infrastructure in Canada, reduce construction cost by the better prediction of the properties of muskeg and a reduction of the maintenance requirements for the structures currently constructed on muskeg.