Hydrodynamics and Associated Scour around a Free-Standing Structure Due to Turbulent Bores

authored by

Philippe April-LeQuéré, Ioan Nistor, Abdolmajid Mohammadian, Stefan Schimmels, Alexander Schendel, Nils Goseberg, Kim Mario Welzel, Clemens Krautwald, Jacob Stolle

Abstract

Forensic engineering field surveys conducted in the aftermath of large-scale tsunamis documented the presence of deep local scour holes around structures caused by extreme inundation occurring during such events. The mechanisms leading to scour in extreme flows are still not well understood, as several physical phenomena influencing the spatiotemporal extent of scour have not been adequately investigated. The authors have conducted an experimental test program that has employed a large square column in the Large Wave Flume of
the Coastal Research Center, Germany, while they also used a state-of-the-art numerical model (FLOW-3D) to numerically reproduce the experimental results. An investigation of the turbulent flow structures observed around the impacted structure showed that these flow structures are largely responsible for the sediment transport during the runup phase, but the turbulent energy was far less intense during the draw-down phase. The weakness of the turbulent structures observed during drawdown indicates that a different physical phenomenon than the one corresponding to the inflow phase is responsible for the sediment transport experienced during inundation drawdown. Due to the rapid low-
ering of the flow depth during the drawdown phase of tsunami inundations, a loss of excess pressure occurs because of the upward pressure gradient forming within the soil. However, the pore pressure measurements taken inside the soil in the physical experiment indicate no sign of upward pressure gradient on the inshore side of the column, which is an observation that is incongruent with previous similar studies and previous theoretical concepts. This difference was explained by a layer of soil that remained with a low water content throughout the test
because the column was installed on dry sand with low permeability, a condition never tested before for pore pressure change caused by tsunami-like waves

Organisation(s)

Coastal Research Centre
Ludwig-Franzius-Institute of Hydraulics, Estuarine and Coastal Engineering

External Organisation(s)

University of Ottawa
Technische Universität Braunschweig
INRS Universite d'avant-garde

Type

Article

Journal

Journal of Waterway, Port, Coastal and Ocean Engineering

Volume

148

No. of pages

17

ISSN

0733-950X

Publication date

09.2022

Publication status

Published

Peer reviewed

Yes

ASJC Scopus subject areas

Water Science and Technology, Ocean Engineering, Civil and Structural Engineering

Electronic version(s)

https://doi.org/10.1061/(ASCE)WW.1943-5460.0000717 (Access: Closed)