Characterization of soil behaviour for earthquake engineering applications

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Fundamental understanding of soil behaviour has mainly been derived from laboratory tests under fully drained or fully undrained conditions, and along specific stress paths. In reality, in-situ stress paths would be dictated by variations in all three principal stresses, and deformation would invariably involve simultaneous changes in pore-volume and pore-pressure. While drained and undrained approximations might be applicable to specific situations depending on the permeability of the soil and the loading rate, there are several instances during which such approximations will not yield satisfactory results. Consequences of instability (in soils) can be catastrophic, and attempts to safeguard against lifeline failures and to mitigate damage in the event of earthquakes often result in huge economic costs. Current seismic design approach is generally conservative as it relies primarily on empirical data to assess the liquefaction hazard. Better understanding of the behaviour of soils under actual in-situ loading paths and drainage conditions is essential to successfully characterize the response of soil masses during earthquakes. Such an understanding will enable the formulation of comprehensive models that will lead to reliable predictions of the response of the geotechnical structures under imposed loads. Better understanding of the effects of environmental factors on soil behaviour is essential to pursue resource development in the north, and to address concerns related to global warming and sustainable development. Site characterization methods that consider simultaneous changes in pore volume and pressure will yield more meaningful results. The outcome of the proposed research will directly contribute to the safety of mine tailings, and hydro dams, and enable confident designs in problematic soils across the country. The objectives of the proposed research are to assess the effects of initial state, the generalised stress path, and partial drainage on the static and seismic response of soils. A systematic study that isolates, and explores each of these variables will be undertaken to provide a fundamental understanding of the effects shear-volume coupled deformation on the constitutive relations, and liquefaction susceptibility. The effect of generalised initial stress conditions, stress path, and the degree of drainage on the stress-strain behaviour of soils and their instability characteristics will be assessed using triaxial, simple shear, and hollow cylinder tests. In addition, the effects of particle shape, over consolidation, and free-thaw cycles on the mechanical behaviour of soils will be assessed. A better understanding of these effects will enable numerical tools to confidently characterize the anticipated field behaviour. Both monotonic and cyclic tests will be carried out under load, and displacement controlled loading modes to properly simulate the anticipated field loading. Triggering of liquefaction will be considered not only as a result of undrained loading, but also under partially drained conditions and under scenarios involving expansive drainage.