Combined abutment and contraction scour in compound channels for extreme flood events

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dc.contributor.advisor Melville, BW en
dc.contributor.advisor Friedrich, H en
dc.contributor.author Xiong, Xiaozhou en
dc.date.accessioned 2017-04-05T02:44:56Z en
dc.date.issued 2016 en
dc.identifier.uri http://hdl.handle.net/2292/32464 en
dc.description.abstract In this PhD project, the combination of abutment and contraction scour is investigated to better understand the scour mechanisms and scour patterns for extreme floods. Close-toreality scour events were physically simulated using models built at 1:45 and 1:30 geometric scales of two-lane bridge prototypes. Scour and flow-measurement experiments under submerged orifice and overtopping flows were carried out. To better understand the effect of vertical contraction on abutment scour, free surface flows were also investigated for similar experimental conditions. The majority of the experiments were carried out in compound channels, simulating abutments set back from the main channel. Spill-through abutments were used in the live-bed scour regime, and both spill-through and wing-wall abutments were used in the clear-water regime. In addition, to better understand the effect of contraction length on abutment scour, and also to verify the long contraction theory for apron-protected, abrupt abutments, a series of long contraction experiments were carried out with vertical-wall abutments. Several major conclusions can be drawn from the results of this project. For the investigated conditions, results show that vertical contraction significantly affects the flow pattern, the temporal development of scour and the final scour bathymetry. Comparing with submerged orifice flows, flow relief of the overtopping flows has a small effect on the near-bottom turbulence and the scour. Flow patterns at the initial state are found to correlate with scour patterns at the equilibrium state. In the bridge section, a “retreating” behaviour of the main channel bank is observed; at the equilibrium state, the side slope of the “retreated” main channel bank is observed to be invariant, presenting a simple geometric relationship between the depth of the scour hole and its location. For unprotected abutments, scour is centred at the upstream corner of the abutment, regardless of contraction length; and for apron-protected abutments, scour differs significantly with contraction length. Numerical and physical modelling work is required in the future to broaden the knowledge of abutment and contraction scour. Also, further research is required to improve the scour countermeasure design for abutments under pressure flows. en
dc.publisher ResearchSpace@Auckland en
dc.relation.ispartof PhD Thesis - University of Auckland en
dc.relation.isreferencedby UoA99264954413702091 en
dc.rights Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated. Previously published items are made available in accordance with the copyright policy of the publisher. en
dc.rights.uri https://researchspace.auckland.ac.nz/docs/uoa-docs/rights.htm en
dc.rights.uri http://creativecommons.org/licenses/by-nc-nd/3.0/nz/ en
dc.title Combined abutment and contraction scour in compound channels for extreme flood events en
dc.type Thesis en
thesis.degree.discipline Civil and Environmental Engineering en
thesis.degree.grantor The University of Auckland en
thesis.degree.level Doctoral en
thesis.degree.name PhD en
dc.rights.holder Copyright: The author en
dc.rights.accessrights http://purl.org/eprint/accessRights/OpenAccess en
pubs.elements-id 621087 en
pubs.record-created-at-source-date 2017-04-05 en


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