Advanced Constitutive Modelling of Soils for Characterization of Seismic Hazard through Nonlinear Dynamic Simulations

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The geological conditions in Eastern Canada make the assessment of seismic hazard challenging. Soft soil layers, such as sensitive clays, atop the bedrock can develop large strains, significantly amplify ground motion, and cause the motion to propagate much further than other geological settings. For example, in the 1988 Saguenay earthquake, the Montreal-Est Hotel de Ville was damaged and had to be torn down despite being situated 300km away from the earthquake's epicenter. The clay layer beneath the building was 17m thick, which was assessed to be the main cause of the building's demise. The seismic waves can also cause seismically induced landslides in sensitive clays because they are susceptible to cyclic softening, which is characterized by a loss of stiffness induced by cyclic loading.******The tendency of a site to amplify or de-amplify ground motion is estimated either with simulations (site response analyses) or empirical site factors. Simulations can be performed using linear, equivalent linear, or nonlinear methods. Nonlinear simulations have proven to be more precise than equivalent linear simulations at shear strains greater than 0.1%, but they require complex constitutive models and are more computationally demanding. Empirical site factors are generally based on a combination of recorded ground motions and equivalent linear simulations. For soft soil profiles, these site factors can be inaccurate and unsafe because of the limitation of equivalent linear simulations and the lack of soft soil profiles in the database of recorded ground motions. These kinds of site factors are derived to capture only 1D site effects, but multidimensional site effects such as basin effects and topographic amplification can also govern site response. Such complex effects can only be captured through 2D or 3D nonlinear simulations, but the latter are complicated because existing constitutive models often require a complex calibration process and often do not model the dynamic behaviour of soils properly, especially at large strains.******The first short term objective is to create two constitutive models for both site response analysis and problems involving cyclic softening adapted to the need of practitioners, where engineers can input a desired behaviour, instead of complex parameters. The second short term objective is to provide regression models for 1D and 2D site factors by combining data and nonlinear simulations, which will reduce uncertainty and thus correct the bias toward soft soil profiles. The third short term objective is to derive a regression model, based on existing cases and simulations, for the probability of the failure of slopes in sensitive clays under earthquake loading. The long term objectives are to gain a better understanding of seismic hazard and to provide better tools to the industry to facilitate the assessment of seismic hazard.