Scouring Around Multiple Structures in Extreme Flow Conditions

Abstract

As world population increases, coastal areas experience an increase in human occupancy. These community locations come with a greater risk of impacts due to extreme natural events. Tsunami, being one of the most unpredictable and most devastating types of extreme hydrodynamic events, received significant attention over the past decades due to the recent extreme events (2004 Indian Ocean, 2010 Chile, 2011 Japan, 2018 Indonesia). The focus of this thesis is on investigating scour around structures generated by tsunami. Scouring was found to be one of the greatest sources of building damage during the 2011 Tohoku Japan Tsunami and, at the date of the redaction of this thesis, this phenomenon is still little understood by the scientific community. The main objective of this thesis is to study the change in scouring when multiple buildings are constructed in close proximity, as opposed to individual elements such as in the case of all previous studies focussed on tsunami-induced scour. This topic was first investigated by the candidate with the use of a numerical model, FLOW-3D, using the large eddy simulation approach and the Nielsen (1992) bed load sediment transport model. The model results showed a significant increase in scouring when a second building was located along the same transversal plane as the building investigated. Then, three structure arrangements were investigated in a comprehensive physical experiment conducted in the new Dambreak Flume of Hydraulic Laboratory of the University of Ottawa, Canada, to study the effects of (1) upstream constriction, (2) lateral spacing and (3) sheltering on tsunami-induced scour. All three structure arrangements showed a significant effect on tsunami-induced scour. A secondary project was conducted in collaboration with the Technical University of Braunschweig, Germany, and the Leibniz University Hannover, Germany. This large-scale physical experiment, performed in the Large Wave Flume of the Leibniz Institute Hannover, Germany, was used to investigate three different research phenomenon that influence tsunami scouring: (1) the wave drawdown on scour around structures, (2) the evolution of flow eddies and (3) the change in the soil’s pore pressure.