Failure Mechanisms and Local Scour at Coastal Structures induced by Tsunamis

Article


Jayaratne, R., Premaratne, Buddhika, Adewale, Abimbola, Mikami, Takahito, Matsuba, Shunya, Shibayama, Tomoya, Esteban, Miguel and Nistor, Ioan 2016. Failure Mechanisms and Local Scour at Coastal Structures induced by Tsunamis. Coastal Engineering Journal. 58 (4), p. 1640017.
AuthorsJayaratne, R., Premaratne, Buddhika, Adewale, Abimbola, Mikami, Takahito, Matsuba, Shunya, Shibayama, Tomoya, Esteban, Miguel and Nistor, Ioan
Abstract

On March 11 2011, an exceptionally large tsunami event was triggered by a massive earthquake offshore, the northeast coast of Japan, which affected coastal infrastructure such as seawalls, coastal dikes and breakwaters in the Tohoku region. Such infrastructure was built to protect against the Level 1 tsunamis that previously hit the region, but not for events as significant as the 2011 Tohoku tsunami, which was categorized as a Level 2 tsunami [Shibayama et al. 2013]. The failure mechanisms of concrete-armoured dikes, breakwaters and seawalls due to Level 2 tsunamis are still not fully understood by researchers and engineers. This paper investigates the failure modes and mechanisms of damaged coastal structures in Miyagi and Fukushima Prefectures, following the authors' post-disaster field surveys carried out between 2011 and 2013. Six significant failure mechanisms were identified for the coastal dikes and seawalls affected by this tsunami: 1) Leeward toe scour failure, 2) Crown armour failure, 3) Leeward slope armour failure, 4) Seaward toe and armour failure, 5) Overturning failure, and 6) Parapet wall failure, in which leeward toe scour being recognized as the major failure mechanism in most surveyed locations. The authors also propose a simple practical mathematical model for predicting the scour depth at the leeward toe of the coastal dikes, by considering the effects of the tsunami hydrodynamics, the soil properties and the type of structure. The key advantage of this model is that it depends entirely on quantities that are measurable in the field. Furthermore this model was further refined by conducting a series of hydraulic model experiments aimed to understand the governing factors of the leeward toe scour failure. Finally, based on the results obtained, key recommendations are given for the design of resilient coastal defence structures that can survive a level 2 tsunami event.

Keywords2011 Tohoku tsunami; Coastal structures; Post-disaster field surveys; Scour failure; Failure modes and mechanisms; Mathematical model; Scour laboratory experiments
JournalCoastal Engineering Journal
Journal citation58 (4), p. 1640017
ISSN0578-5634
1793-6292
Year2016
PublisherWorld Scientific Publishing
Accepted author manuscript
License
Accepted author manuscript
Accepted author manuscript
Digital Object Identifier (DOI)doi:10.1142/S0578563416400179
Publication dates
Print09 Dec 2016
Publication process dates
Deposited19 Oct 2016
Accepted19 Oct 2016
Accepted18 Oct 2016
FunderJapanese Ministry of Education, Culture, Sport, Science and Technology
Great Britain Sasakawa Foundation
University of East London
Japanese Ministry of Education, Culture, Sport, Science and Technology
Great Britain Sasakawa Foundation
University of East London
Copyright informationElectronic version of an article published as, Failure Mechanisms and Local Scour at Coastal Structures induced by Tsunamis, Coastal Engineering Journal, 58(4): 1640017, 10.1142/S0578563416400179 © 2016 World Scientific Publishing Company http://www.worldscientific.com/worldscinet/cej
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