Characterization of soil behaviour for earthquake engineering applications

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Current seismic design approach is generally conservative as it relies primarily on empirical data to assess the liquefaction hazard. As a result, attempts to safeguard against possible lifeline failures during earthquakes often result in huge economic costs. Better understanding of the behavior of soils under actual in-situ loading paths and drainage conditions is essential to properly characterize the response of soils during earthquakes. It will enable the formulation of comprehensive models that will lead to reliable predictions of the response of the geotechnical structures under imposed loads.******Fundamental understanding of soil behavior has mainly been derived from laboratory tests under fully drained or fully undrained conditions 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 yield sufficient accuracy under specific situations, there are several instances during which such approximations will not yield satisfactory results. ******Insights into the liquefaction phenomena have generally been elicited by simulating the propagation of body waves (often a vertically propagating s-wave). But, a large number of liquefaction failures occur due to surface-wave loading. At present virtually nothing is known about whether current understanding applies to liquefaction due to surface waves (e.g., Rayleigh wave) or combined body waves (simultaneous p- and s-waves). The proposed research is the first ever attempt to simulate the stress conditions due to Rayleigh (or simultaneous p- and s-) waves using a hollow cylinder torsional shear (HCT) device. This is a completely new line of inquiry in experimental research and our laboratory is one of the very few in the world that can explore the response of soils along such complex stress paths.******Proposed research on the effects of 3D loading paths on Leda clay also contains several novel and innovative elements. The new HCT sample trimmer will allow using a given high-quality undisturbed Leda clay specimen (obtained using the Laval sampler) for one HCT test, and up to 12 triaxial or 8 simple shear tests (or a combination of the two). This is the first such attempt ever where an HCT specimen is prepared while preserving the inner core for triaxial and/or simple shear tests.******Improved understanding of the effects of environmental factors on soil behavior 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 infrastructure, mine tailings and hydro dams.**