Multiphysics modelling and photogrammetry applied to the study of Champlain clays and their geotechnical properties

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Champlain clays underlie a large part of the densely populated Saint Lawrence River valley in Eastern Canada. These clays are known for their high sensitivity to remoulding and their high compressibility. These properties often lead to costly earthflows and large settlements for structures.***Novel experimental methods and numerical modelling tools offer new opportunities in the study of Champlain clays and their geotechnical properties. Multiphysics modelling (e.g., finite-element code COMSOL) allows different phenomena to be coupled, complex boundary conditions to be applied and user-specified differential equations to be solved. On the experimental side, image analysis techniques, like photogrammetry, allow displacement fields to be evaluated and used in the calibration of numerical models. The applicant proposes to apply these techniques in three research projects.****The first project will combine micropaleontology and multiphysics modelling to determine the effect of initial or depositional pore water salinity on clay sensitivity. Microfossil assemblages will be used to estimate the clay depositional salinity for sites in Lachenaie, Quebec. These initial salinity profiles will be validated in a coupled COMSOL-PHREEQC model of the chemical evolution of the pore fluid since the Champlain Sea retreat.****In the second project, photogrammetry will be used to monitor the deformation induced by a circular footing in the laboratory. The footing will rest on an artificial Champlain clay layer instrumented with pore pressure and displacement transducers. Digital cameras will be used to take pictures of the clay surface as it deforms. Displacements will be calculated with VMS, a photogrammetry software package. The experimental data will be used to calibrate a geomechanical model in COMSOL.****In the third project, COMSOL will be used to verify the impact of climate change on the geotechnical engineering of Champlain clays. Pore pressure data collected in Lachenaie since 2012 will be modelled using COMSOL and data from nearby weather stations. Boundary conditions based on climate change models for Southern Quebec will be applied in the numerical model to evaluate the impact of climate change on slope stability and settlement.****Training geotechnical engineers that are familiar with Champlain clays remains a top priority for the geotechnical community of Eastern Canada. The Saint-Jude earthflow of 2010 bears witness to ever-present difficulties in predicting Champlain clay behaviour. The three projects will introduce a new numerical analysis tools (COMSOL). The projects will lead to a better understanding of Champlain clay properties and a new family of photogrammetric methods for structure monitoring in the field.***