Defining the operational strength of peat (muskeg)

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Muskeg and peat soils cover 18% of Canada's landmass and is primarily concentrated within the northern regions. A strong understanding of the engineering properties of muskeg is important for the construction and maintenance of transportation infrastructure in these regions. Defining the strength of highly fibrous peats is still elusive, as peat linearly strain harden and thus does not develop a maximum value that can be defined as a strength. Further, traditional geotechnical testing methods used to evaluate peat cannot evaluate tensile stresses generated by the fibrous structure. My research and a review of others' led to the hypotheses that highly fibrous peat, inclusive of the full effects of fiber reinforcement, fails at a tensile stress state; testing at this stress state can be accomplished with triaxial tests with extension stress paths; and the strength of this type of peat is poorly defined by a Mohr-Coloumb surface. Thus, Objective i is to quantify the tensile stresses generated within fibrous peat and fiber reinforced soils; specifically, how tension in fibers are incorporated into strength and manifest in the mechanism of failure. This research will evaluate the effects of fibers in peat and fiber reinforced clays, and then develop an understanding of how this tensile behaviour of fibrous soils manifests for bearing capacity. My past PhD student and I observed the seasonal increase of pore pressure (u) in peat beneath railway embankments well above hydrostatic pressure followed by a rapid decrease. This was found to be the result of gas generation and is controlled by temperature. The presence of gas and increased pore pressure was found to push fluid flow as a thermally driven consolidation mechanism and reduce effective strength. This led to the hypothesis that the estimated increases of mean temperature from 1.4oC to > 4oC for northern Alberta over the next 30 years will result in longer periods of accelerated degradation and thermally driven consolidation and that this sensitivity to temperature has the potential to negatively impact northern infrastructure. Thus, Objective ii is to evaluate the regional susceptibility of peat to gas generation and thus thermally driven consolidation and reduced strength; and to quantify the sensitivity of the rate of gas generation to increased temperatures that have been observed and predicted for these regions. Three sites in different regions of Canada will be instrumented to measure u resulting from gas generation at the start of the research program. The data and thermal modeling will determine the temperature profiles resulting from the differing climate change scenarios and evaluate the potential for increased degradation and associated gas generation. This study will further develop a fundamental understanding of the properties of muskeg and peaty soils, and thus impact the development in northern regions and the safety and reliability of Canada's infrastructure.