Thermo-Hydraulic-Mechanical Properties of Frozen and Thawing Soils

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The North is forty percent of Canada’s land mass. With world-class mineral, oil and gas deposits, the North is a place of tremendous economic opportunity. Sustainable resource development in the North requires to design and build infrastructures such as access roads, water retaining structures, pipelines, mining installations, ports, airports and buildings. The North is also on the front line of climate change impacts and adaptation. Strong environmental protection is an essential component of sustainable development, especially in a permafrost environment. Adequate protection is provided if the freeze-thaw effects are well understood and adapted to the climate change trends. This research proposal addresses several issues: • Thaw-consolidation in a two of three dimensional environment; • Creep behaviour of ice-rich soils at temperatures higher than -1 °C; • Shear strength of thawed materials and slope stability. Thaw-consolidation Morgenstern and Nixon (1971) have studied the thaw-consolidation process in a one-dimensional formulation and using analytical techniques with its inherent simplifications. Their analysis showed that the pore pressure distribution in the thawed soil can be related to the thaw-consolidation ratio, R, which is a parameter coupling thaw rate and rate of water drainage away from the thaw front. The main assumption was that the thawed soil did not settle until thaw was complete. Needless to say that thaw settlements van reach up to 70% in ice rich soils and neglecting settlement during the analysis leads to overly conservative design. This research proposal uses modern computing tools to derive a solution in which the processes are fully coupled. Flex-PDE will allow to couple drainage in the thawed soil, thaw front propagation and consolidation with a moving boundary at the surface in one, two or three dimensional environments. New pore pressure charts will be established and a methodology for analysis specific problems (foundations, roads, pipelines and earth dams, slope stability in thawing slopes) will be proposed. Creep behaviour of ice-rich soils at temperatures higher than -1°C When a frozen soil is subjected to a load, it will respond with an instantaneous deformation and a time-dependent deformation. The rate effects are temperature- and stress-dependent and vary with the amount of ice present in the frozen soil. In the literature one finds a significant amount of data for frozen soils are temperature lower than -1°C. However, considering a climatic change of several degrees per hundred years, more study need to be conducted for ice-rich soils at temperatures higher than -1°C. This is particularly important for the case of slopes in which ice lenses have formed parallel to the sloping ground. These slopes may display creep rates as high as 2m/year, identically to the behaviour of glaciers in the Swiss Alps. Laboratory tests will be conducted in environmental chambers controlled to a specific temperature with a variation of less than 0.05°C in order to obtain creep parameters and constitutive equations. Flex-PDE will be used to study the behaviour of slopes and other structure using the parameters at high temperatures. Shear strength of thawed soils The proposed research will also investigate the relationship between shear strength and degree of pore pressure dissipation in thawing soils. Little data is available and is needed for adequate design during thaw for ensuring stability of structures built on permafrost.