Physical Modelling of Instability in Granular Soils and Tsunami Hazards Associated with Coastal Slope Failures

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Treflik-Body, Erica J.
tsunami hazards , submarine landslides , landslide generated waves , granular collapse , physical modelling
Coastal mass failures such as submarine and subaerial landslides have the potential to create significant tsunami hazards. As an inherently coupled solid-fluid interaction problem, accurate assessment of these hazards requires an understanding of the triggering mechanisms of failure to predict the consequential wave generation upon impact. With respect to triggering mechanics, failures of submarine slopes have been observed to occur at perplexingly low inclinations, which could be a result of soil instability. In this study, large-scale tilt table testing under dry and submerged conditions were conducted with imbedded shear stress and strain sensors to quantify the constitutive behaviour and pore pressure response of loosely placed sand leading up to and during instability. Multiple instability events were observed in the dry specimen whereas a single instability event at lower inclinations occurred for submerged samples at the same initial void ratio. The pore water pressure response following instability was consistent with the material coefficient of consolidation for liquified soils. Wave consequences were explored through large scale granular collapse experiments conducted with a new vertical lifting gate facility. Granular columns under varying levels of submergence were released and the wave generation, propagation and runup were captured through wave capacitance gauges and cameras. Both the seaward- and landward-directed waves associated with fully submerged failures were quantified. The observed seaward wave amplitudes agree with existing empirical relationships developed from small scale testing and a new analytical solution for the landward wave amplitude is presented. A sample of these large-scale tests were numerically simulated using a coupled DEM-LBM model, which adequately captured the landward and seaward wave characteristics and behaviours.
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