Wave generation due to the collapse of partially and fully submerged granular columns in large-scale laboratory experiments

Abstract

Under changing climate, coastal regions are increasingly vulnerable to a variety of hazards, including rapid subaerial and submarine landslides. These hazards can generate tsunamis and dense turbidity currents, which threaten both onshore and offshore infrastructure. Due to the complex geomechanics of failure, limited physical modelling has been conducted that encompasses both the triggering of granular landslides and subsequent waves associated with partially and fully submerged mass failures. Further, experimental modelling of submerged failures has primarily focused on the waves generated in the direction of failure (seaward) and not on the waves formed above and behind the failure (shoreward). To this effect, a series of large-scale granular collapse experiments were conducted by releasing 0.75 m and 0.5 m tall columns of 9.25 mm nominal diameter river stone into reservoir depths ranging from 0.20 m to 1.10 m to explore the wave generation and runup processes in both seaward and shoreward directions. The columns were released by a pneumatically-actuated vertically rising gate designed for the 2.10 m wide and 1.20 m high glass-walled flume. The gate lifts rapidly in 0.7 s, which enables the instantaneous loss of support of the source volumes and results in granular collapse. The wave amplitude is measured using wave capacitance gauges and the failure mechanics are captured with high speed cameras. Overall, the wave amplitudes measured in these highly instrumented large-scale physical models are in good agreement with empirical relationships developed in a previous study using smaller-scale models. The large-scale experimental results provide insight and opportunity to develop relationships between the initial column submergence depth and the magnitude of the shoreward propagating waves, which has previously not been explored. Connecting the amplitude of the waves with the tsunamigenic potential for partially to fully submerged granular materials will assist in understanding risk to offshore infrastructure and communities in coastal regions.