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Three dimensional method for monitoring damage to dolos breakwaters

dc.contributor.advisorSchoonees, J. S.en_ZA
dc.contributor.authorTulsi, Kishan Rameshen_ZA
dc.contributor.otherStellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.en_ZA
dc.date.accessioned2016-12-22T13:17:44Z
dc.date.available2016-12-22T13:17:44Z
dc.date.issued2016-12
dc.identifier.urihttp://hdl.handle.net/10019.1/100122
dc.descriptionThesis (MEng)--Stellenbosch University, 2016.en_ZA
dc.description.abstractENGLISH ABSTRACT: Ports are frequently protected by breakwaters which are designed to withstand harsh environmental conditions over long periods of time. However, in most cases, they gradually or suddenly deteriorate before they reach their design life. In order to extend the design life of breakwaters, regular damage investigations and timeous repairs are required. One of the important aspects is calculating the severity of damage to breakwaters. Traditionally, breakwater inspection has been done using aerial photographs and underwater imaging to accomplish these investigations. Breakwaters are systematically divided into inspection stations and photographs are taken to inspect and assess the damage. The photographs are then visually compared with the previous inspection photographs to identify changes. This is difficult to achieve as it is not always possible to get the helicopter exactly in the same position on every survey and highly dependent on the skill of the helicopter pilot. Another difficulty is taking underwater images near the breakwater due to poor visibility and wave breaking. A major disadvantage of the aerial photographic method is that it only provides a two dimensional (2D) picture of the breakwater above water. The inter-tidal zone on a breakwater slope is where damage usually occurs. It is difficult to capture data in this zone, particularly due to wave action, which results in poor visibility. Ideally, a method is required to capture and assess damage above and below water. High resolution laser scanning and acoustic technologies are available to inspect breakwaters above and below water. These are light detection and ranging (LIDAR) and multibeam echo sounders respectively. The South African coastline has few significant embayments’ that can provide natural shelter from the high energy wave regime on the coastline. Consequently, South African ports require protection in the form of heavy armoured breakwaters and seawalls. Maintenance of these defences is critical for the safe functioning of these ports. Rapid assessment of damage to breakwaters and seawalls which is cost e↵ective is necessary to ensure that repairs are undertaken timeously. This study explores the use of LIDAR and multibeam echo sounders, instead of the traditional aerial photography, to assess damage to breakwaters in general. Three dimensional (3D) data analysis using LIDAR and multibeam echo-soundings (as investigated in this thesis) is aimed at providing a more realistic method to quantify damage above and below water rather than two dimensional (2D) photographs. The objective of this study was to evaluate the accuracy of a 3D method using the LIDAR and multi-beam echo sounder data to quantify damage to dolos breakwaters above and below the water surface (including the inter-tidal zone). This was aimed towards the development of the 3D eroded volume method (3D method). The investigation began with an idealized undamaged model breakwater slope in a laboratory experiment comparing the repeatability of the 3D method with sequential scans and the photographic method in an attempt to compare the deviation in repeatability of data captured. Thereafter three degrees of artificial damage were created to the slope of the model breakwater in the form of settlement, intermediate damage and failure of a localized area of the dolos armour layer. The 3D method was then applied to a 3D physical model study of the spur breakwater at the root of the Table Bay main breakwater. Field data of the spur breakwater were then captured with the 3D method and compared with the most recent 2D aerial photographic survey. More than two decades of 2D aerial photography damage assessment data of the spur breakwater were available to establish a baseline. The 3D method data captured were compared with the visual 2D field data to determine the 3D methods accuracy. The comparison of the cumulative damage progression monitored by the visual 2D photographic method with that calculated by the 3D method, showed that there is a good correlation between the two damage quantification methods. The cumulative percentage damage obtained from the 2D visual analysis records has a mean di↵erence of 10% in comparison to the 3D method. The results of the 2D and 3D methods di↵er in cases of small settlements and larger displacements. This study has led to an advance in the quantitative 3D assessment of di↵erent degrees of damage to breakwaters with dolos armour units above and below water. The 3D method used to assess the extent of damage to a breakwater was compared against the conventional visual method described by Phelp (1995). A marginal variation between the two methods was found, however the 3D method which quantifies 3D eroded volume is recommended for future breakwater investigations to provide a better quantifiable above and below water assessment.en_ZA
dc.description.abstractAFRIKAANSE OPSOMMING: Hawens word gewoonlik beskerm deur golfbrekers wat ontwerp word om storm toestande oor n lang tydperk te weerstaan. Weens moeilik voorspelbare golftoestande gebeur dit dat golfbrekers (veral rotsvul tipe golfbrekers) geleidelik of skielik skade ondevind voor hul ontwerp leeftyd. Om te verseker dat golfbrekers hul stabiliteit behou, is dit belangrik dat gereelde inspeksies/opnames gedoen word om moontlike skade te identifiseer om sodoende tydige herstelwerk te kan doen. Van uiterse belang met die inspeksies is dat skade gekwantifiseer word om die graad van skade te definieer.. Tradisionele metodes om die skade van golfbrekers bo water (en gedeeltelik onder water) te dokumenteer sluit in lugfotos vanaf voorafbepaalde vaste posisies vanuit n helikopter. Hierdie opnames word dan visueel vergelyk met vorige opnames om veranderinge tussen opnames te identifiseer. Hierdie metode het bepaalde leemtes soos byvoorbeeld dat die voorafbepaalde vaste posisies van waar fotos geneem moet word, moeilik deur deur n helicopter gehandhaaf kan word. Verder is dit moeilik om goeie kwaliteit fotos te verkry in die onderwater gedeeltes weens golfbreking en swak sigbaarheid deur die water. ’n Groot leemte van die lugfoto-metode is dat dit slegs ’n twee-dimensionele beeld (2D) van die golfbreker dokumenteer. Die inter-getysone op ’n golfbreker helling is die gebied waar die meeste skade gewoonlik voorkom. In die sone is dit moeilik om die data op betroubare inligting te bekom weens golf aksie en swak sigbaarheid. Daarom is dit nodig om ’n metode te ontwikkel wat skade beide bo en onder water e↵ektief en kwantitatief kan bepaal. Ho resolusie laser skandering en akoestiese tegnologie is beskikbaar om die golfbrekers bo en onder die water in drie dimensies (3D) op te meet. Dit sluit in die sogenaamde LIDAR metode (wat bebruik maak van laser posisie bepaling) en die ”Multi-beam echo sounder” metode. Suid Afrika se kuslyn het net ’n paar beduidende baai-gebiede wat natuurlike beskerming teen ho energie golwe vanuit die suidelike oseaan bied. As gevolg hiervan benodig Suid Afrikaanse hawens grootskaalse gofbreker beskerming in die vorm van bewapende golfbrekers en see mure. Onderhoud van die stukture is van uiterse belang om veilige gebruik van die hawens te verseker. Dit is daarom nodig dat hierdie gofbreker strukture dikwels en op n gereelde basis ondersoek word vir moontlike skade om derhalwe herstelwerk, waar nodig, betyds te doen. Hierdie studie het die gebruik van LIDAR en multi-straal eggo-peiling metode ondersoek om die skade aan golfbrekers in 3D te bepaal. Hierdie metodes is gebruik omdat dit veranderinge in die oppervlakte van n golfbreker in 3D kan opmeet die ontblote oppervlakte van n golfbreker kan met hierdie metodes baie na aan kontinu in die x-, y- en z-vlakke vasgel word. Die doel van hierdie studie was om die akkuraatheid te evalueer van n 3D metode deur gebruik te maak van die LIDAR en multi eggo peilings data om die skade van n Dolos (golfbreker) bo en onder die water oppervlakte te kwantifiseer (insluitend die getysone). Hierdie ondersoek was gerig om n 3D erosie volume metode (3D metode) te ontwikkel. Die ondersoek is begin met n ge-idialiseerde onbeskadigde Dolos model golfbreker helling in ’n laboratorium eksperiment waar die herhaalbaarheid van die 3D metode saam met die fotografiese metode bepaal is. Dieselfde heraalbaarheids evaluering is gedoen met drie grade van skade wat kunsmatig aan die model golfbreker se helling aangebringsis nl. versakking, tussen stadium skade en faling van n lokale gedeelte van die Dolos beskermingslaag. Die 3D metode was hierna toegepas op ’n 3D fisiese model van n gedeelte van die bestaande Tafelbaai se hoof golfbreker. Veld-data van dieselfde gedeelte van die Tafelbaai se golfbreker was daarna versamel met die 3D metode en vergelyk met die mees onlangse lugfotos van dieselfde gedeelte van die golfbreker. Meer as twee dekades se lug-fotografiese data van die golfbreker skade was beskikbaar om ’n grondslag te vestig vir die ondersoek. Die data van die 3D metode en die data verkry van die lugfotos (2D metode) is hierna vergelyk om die akkuraatheid van die 3D metode te bepaal. Hierdie vergelyking het getoon dat daar ’n sterk korrelasie tussen die 3D metode en die lugfoto metode is. Die kumulatiewe persentasie skade verkry van die 2D lug-foto metode het ’n gemiddelde verskil van 10 persent met dit verkry van die 3D metode. Die resultate het wel afwykings tussen die twee data stelle getoon. Die afwykings was gevind waar daar klein versakkings en groot verplasings voorgekom het. Die studie het gelei to die verbetering in die kwantifisering van skade aan Dolos golfbrekers deur middel van n 3D metode wat die skade aan n golfbreker in terme van die volume skade bo en onder water bepaal. Hierdie 3D metode is vergelyk met die konvensionele visuele metode, wat beskryf word deur Phelp (1995). ’n Minimale variasie tussen die twee metodes was gevind. Aangesien die 3D metode n beter kwantitatiewe skade bepaal in terme van volume skade bo en onder water, word dit aanbeveel vir toekomstige golfbreker monitering.af_ZA
dc.format.extentxix, 141 pages : illustrationsen_ZA
dc.language.isoen_ZAen_ZA
dc.publisherStellenbosch : Stellenbosch Universityen_ZA
dc.subjectBreakwaters -- Deteriorationen_ZA
dc.subjectBreakwaters -- Maintenance and repairen_ZA
dc.subjectThree-dimensional imagingen_ZA
dc.subjectUCTDen_ZA
dc.titleThree dimensional method for monitoring damage to dolos breakwatersen_ZA
dc.typeThesisen_ZA
dc.rights.holderStellenbosch Universityen_ZA


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