Hydraulic stability of Cubipod armour units in Breakingconditions Lien Vanhoutte

149 Pages·2009·11.6 MB·English

Hydraulic stability of Cubipod armour units in
Breakingconditions

Lien Vanhoutte

Promotor: Prof. Josep Medina (UPV Valencia)
Co-Promotor: . Prof. dr. ir. Julien De Rouck

Masterthesis to obtain the degree:
Master of Science in Civil Engineering

Laboratory of Ports and Coasts, Polytechnic University of Valencia
Departement of Civil Engineering, Ghent University
Academic year 2008-1009
i
Preface
I would like to thank my tutor of this project Prof. Medina for giving me the great opportu-
nity to make my (cid:28)nal year project at the Laboratory for Ports and Coasts of the Polytechnic
University of Valencia, and for his guidance throughout the project.
Special thanks also to Prof. De Rouck as my Erasmus-coordinator and co-tutor of this thesis
for providing the possibility of this abroad experience.
Deep gratitude goes to Guille, for his guidance throughout the project, for sharing his ex-
perience, for helping me with every single doubt, for encouraging me and helping me out in
the stressful moments. A warm thanks as well to Jorge, Vicente, Kike, Mireille, Steven, CØsar
and Pepe, for providing a very nice working space in the laboratory.
Finally I want to thank my parents, my sisters, friends, and (cid:29)at mates in particular, for
their support and many hours of listening during this thesis.
COPYRIGHTS
The author grants the permission for making this thesis available for consultation and for
copying parts of this thesis for personal use.
Any other use is subject to the limitations of the copyright, speci(cid:28)cally with regards to the
obligation of referencing explicitly to this thesis when quoting obtained results.
1st of June 2009,
Lien Vanhoutte
ii
Overview
Hydraulic stability of Cubipod armour units in
breaking conditions
Author: Lien Vanhoutte
Master thesis to obtain the degree of Master of Civil Engineering
Academic year 2008-2009
Tutors:
Prof. Josep R. Medina, Laboratory of Ports and Coasts, Polytechnic University of Valencia
Prof. Julien De Rouck, Department of Civil Engineering, Ghent University
Summary
In this report, the study of the new armour unit, Cubipod, designed by the Laboratory of
Ports and Coastas of the Politecnic University of Valencia, is described. The general stability
of mound breakwaters are discussed and an overview of di(cid:27)erent existing armour elements is
given. Further, the wave height distribution in shallow water is analysed theoretically and
compared with the obtained results. An experimental study of the Cubipod armour unit is
carried out on a physical scaled mound breakwater model in breaking conditions. Results on
re(cid:29)ection and damage progression are presented and compared with previous similar tests in
deepwater conditions. A (cid:28)rst estimation of the hydraulic stability coe(cid:30)cient of the Cubipod
in breaking conditions is proposed. The results show that the Cubipod has low re(cid:29)ection and
high hydraulic stability.
Keywords: Cubipod - armour unit - mound breakwater - hydraulic stability - breaking
conditions
H C
YDRAULIC STABILITY OF UBIPOD ARMOUR
UNITS IN BREAKING CONDITIONS
L.Vanhoutte1
Supervisor(s): J.R.Medina2,J.DeRouck3
1Masterthesisstudent,FacultyofEngineering,GhentUniversity,Belgium
2Professor,Lab.ofPortsandCoasts,PolytechnicUniversityofValencia,Spain
3Professor,FacultyofEngineering,GhentUniversity,Belgium
Abstract—InthisMasterthesisanexperimentalstudyoftheCubipodar- TheCubipodarmourunitisdesignedtobenefitfromthead-
mourunitwascarriedoutonaphysicalmodelbreakwaterinshallowwater. vantages of the traditional cube, but to correct the drawbacks.
TheCubipodisanewarmourunit,designedbytheLaboratoryofPortsand
Therefore,thedesignoftheunitisbasedonthecubeinorderto
CoastsoftheUniversidadPolitcnicadeValencia. Asthewaveheightisan
obtainhisrobustness. TheprotuberancesoftheCubipodavoid
importantvaluewhendesigningmoundbreakwaters,theoriesestimating
themaximumwaveheightinbreakingconditionswerestudiedandcom- face-to-face settlement and increase the friction with the filter
paredwiththemeasuredresultsintheLaboratory. Resultsonreflection layer as can be seen in figure 1. They avoid sliding of the ar-
anddamageprogressionwerepresentedandcomparedwithprevioussim-
mourelementsandthus,HeterogeneousPackingandlossofel-
ilartestsindeepwaterconditions. Anestimationofthehydraulicstability
KD coefficientoftheCubipodinbreakingconditionswasproposedusing ementsabovethestillwaterlevelisreduced. Allthisindicatesa
theVirtualNetMethod[2]. TheresultsshowthattheCubipodhaslowre- higherhydraulicstabilityofCubipodsincomparisonwithcube
flectionandahighhydraulicstability.
elements,whichwasprovedinearlierexecutedtests[3].
Keywords—Cubipod-armourunit-moundbreakwater-hydraulicsta-
bility-breakingconditions
I. INTRODUCTION
Mound breakwaters play an important role in the protection
of harbours. They have many failure modes, but the most im-
portantoneisthelossofhydraulicstabilityofthearmourlayer
under wave attack. This can be caused by direct extraction of
armourunits,orbyexcessivesettlementcausingHeterogeneous
PackingofthearmourlayerasdescribedbyGomez-Marton&
Medina[2].
Generally, mound breakwaters are placed in shallow water Fig.1. Thenewarmourunit:theCubipod
and thus subjected to breaking conditions. An important fac-
tor influencing the hydraulic stability is the maximum incident
III. EXPERIMENTS
wave height. Hydraulic stability of armour layers has been in-
tensively studied in literature and several formulae have been Regular experiments on five different physical model break-
proposedforpredictingarmourdamage. Thefirstmodelswere waterswerecarriedoutinthe2Dwaveflumeofthelaboratory
onlyvalidforstationaryconditions. In1988,VanderMeer[8] ofPortsandCoastsinthePolytechnicUniversityofValencia.A
proposed a first formula for irregular waves. Medina [7] pro- sectionwithadoublelayerofCubipods,onewithasinglelayer
posed a method applicable to nonstationary conditions, based ofCubipods,eachwithandwithouttoebermwereconsidered.
onanexponentialmodelforindividualwavesofthestorm. The Finally,experimentswerecarriedoutonasectionconsistingof
mostfrequentlycitedarmourstabilityformulawaspublishedby acubelayercoveredbyaCubipodlayer.
Hudsonin1959[4]forregularwaves,andlaterpopularizedfor The unit weight of the Cubipods is 128g, and they have a
irregularwavesbySPMusingtheequivalencesH1/3 andH1/10 densityof2300kg/m3. Thewaterdepthchangesfrom30cmto
asrepresentativeofthewaveheight. 42 cm near the model. For every water depth different periods
wereconsidered,lancingwaveswithincreasingwaveheightfor
II. ARMOURUNITS
everyperiod. Thewaveheightwasincreaseduntilbreakingoc-
Originally, harbours were built with wooden or stone con- cured. Registered wave heights were separated in incident and
structions. The continuous growing of the harbours meant a reflectedwaveswiththeLASAV-method(Figueres&Medina
need for higher stones and design of artificial concrete armour [1]), and the reflection coefficient was obtained as CR [%] =
units was forced. Many different breakwater armour units ex- H /H . Damage progression was analysed visually, establish-
r i
ist, each with their own advantages and disadvantages. Their ing the damage levels Initiation of Damage, Iribarren Damage
characteristicshaveanimportantinfluenceonthehydraulicsta- andDestruction,aswellasquantitatively,usingtheVirtualNet
bilityofthemoundbreakwaterandexplainswhyimprovement MethodproposedbyGmez-Martn&Medina[2],whichallows
anddevelopmentofarmourunitsisstillanimportantsubjectof tomeasurealsothefailuremodeofHeterogeneousPacking,and
research. notonlyextractionofarmourunits.
IV. RESULTS for a double layer of Cubipods with toe berm and KD=23 for
a single layer were found. K =18 was found for a combined
A. Breakingwaveheight D
armour layer with cubes and Cubipods. Comparison between
The incident wave height is an important factor influencing thedamageprogressionindeepwaterconditionsandinshallow
thedesignofcoastalstructures. Anoverlyconservativeestima- watershowsusthatK inshallowwaterislessthanindeepwa-
D
tion of this value can greatly increase costs and make projects terconditions. Waveswithhigherenergyreachthebreakwater,
uneconomical, whereas underestimation could result in struc- whichmeansthatthedamage willinitiateearlierthanindeep-
turalfailureorsignificantmaintenancecosts.Ashortstudycon- waterconditions. InFig. 3,thedamageprogressionforthedif-
cerning the maximum wave height in breaking conditions was ferent breakwater sections are shown, with D the linearized
0,2
executed. dimensionless damage proposed by Medina [6] and indication
Different theories exist to estimate this maximum value. oftheInitiationofdamageandInitiationofIribarrendamage.
Many theories however, overestimate this value. Further, they
suppose mostly that the energy from the broken waves is con-
centratedinthebreakingwaveheight,whichmeansthatallthe
brokenwaveshavethebreakingwaveheightinthesurfingzone.
Thisstatementhoweverdidn’tcorrespondwiththereality. The
energy from the broken waves was distributed back over the
smallerwaveheightsinthedistribution. InFig. 2isthetheory
ofLeRoux(2007)[6]showntoestimatetherealwaveheights.
The estimation is similar to the measured values, however, he
underestimates the breaking wave height and supposes a con-
stant wave height after breaking, independent of the wave pe-
riod.
Fig.3. Lineariseddimensionlessequivalentdamageasafunctionofdimension-
lesswaveheightforthedifferentstudiedbreakwatersections
V. CONCLUSION
Calculatingamoundbreakwaterinbreakingconditions,spe-
cial attention has to paid to the maximum wave height. Many
existing theories overestimate this wave height, which can re-
sult in uneconomical results. According to the executed tests,
theCubipodprovestohaveahighhydraulicstabilityinbreak-
ing conditions and shows to be a very promising armour unit,
withasimpleandrobustshape,aneasyplacementpatternanda
highhydraulicstabilitycomparedwithotherarmourunits,also
inbreakingconditions.
VI. BIBLIOGRAPHY
(1)Figueres,M.&Medina,J.R.:Estimationofincidentandreflectedwaves
Fig.2. GraphicshowingthetheoryofLeRoux(2007)[5]toestimatethewave
usingafullynonlinearwavemodel. Proc. ofthe29thCoast. Eng. Conf.,pp.
height,comparedwiththemeasuredresultsintheLaboratory
594-603,2004.
(2)Gomez-Martin,M.E.&Medina,J.R.:Analisisdeaverasdediquesentalud
B. Hydraulicstability conmantoprincipalformadoporbloquesdehormigon.VIIIJorn.Espaolasde
Ing.deCostasyPuertos,2005.
The reflection coefficient differs between 10% and 30% for (3)Gomez-Martin, M.E.&Medina, J.R.: Cubipodconcretearmourunitand
HeterogeneousPacking.ProcofCoast.Structures,ASCE,2007.
kh>1,5andincreasesuntil50%forsmallkhvalues. Forhigh
(4)Hudson:Laboratoryinvestigationofrubblemoundbreakwaters. J.Wtrwy.,
kh values, the type of armour layer has a big influence on the Port,Coast.andOc.Division,85(3):93-121,1959.
reflectioncoefficientandasinglelayerreflectslessenergythan (5)LeRoux,L.: Asimplemethodtodeterminebreakerheightanddepthfor
a double layer. For small values of kh, however this influence differentdeepwaterheight/lengthratiosandseafloorslopes. CoastalEngr. 54,
271-277,2007.
decreases and becomes nil. Reflections coefficients in shallow
(6)Medina,J.R.,Hudspeth,R.T.andFassardi,C.: Breakwaterarmordamage
water is lower than in deepwater conditions because the crest duetowavegroups.J.Wtrwy.,Port,Coast.andOc.Engrg.,ASCE,120(2),pp.
breaksandalotofenergyisdissipatedwhichmeanslessreflec- 179-198,1994.
(7)Medina,J.R.:Waveclimatesimulationandbreakwaterstability.Proc.ofthe
tion.
25thCoast.Eng.Conf.,ASCE,pp.1789-1802,1996.
Damage analysis resulted in a higher hydraulic stability for (8) Van der Meer, J.W.: Suitable wave-height parameter for characterizing
sectionswithtoeberm,becausethereisnoincreaseofporosity breakwaterstability.J.ofWaterw.,Port,Coast.andOc.Eng.,ASCE,114(1):66-
80,1988.
at the bottom of the breakwater. Those are the common built
breakwatersections. HydraulicstabilitycoefficientsofK =28
D
Contents
Extended abstract ii
List of Figures ix
List of Tables xiii
1 Introduction 1
2 Stability of Mound Breakwaters 4
2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.2 A Short History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.3 Analysis of the stability of a mound breakwater . . . . . . . . . . . . . . . . . . 9
2.3.1 General stability of a mound breakwater . . . . . . . . . . . . . . . . . . 9
2.3.2 Heterogeneous packing . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.3.2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.3.2.2 Heterogeneous packing. . . . . . . . . . . . . . . . . . . . . . . 12
2.3.3 Damage criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
2.4 Quantization of the stability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
2.4.1 Formula to calculate the stability of a mound breakwater . . . . . . . . 16
v
Contents vi
3 Armour Units 18
3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
3.2 History: the armour units since the 50’s . . . . . . . . . . . . . . . . . . . . . . 19
3.3 Classi(cid:28)cation of armour units . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
3.4 A new armour unit: The Cubipod . . . . . . . . . . . . . . . . . . . . . . . . . 28
3.4.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
3.4.2 Idea . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
3.4.3 Concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
4 Wave height in breaking conditions 33
4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
4.2 The surf zone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
4.3 Types of breaking waves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
4.4 Models to estimate the wave height distribution . . . . . . . . . . . . . . . . . . 36
4.5 Maximum wave height in breaking conditions . . . . . . . . . . . . . . . . . . . 38
5 Experimental setup 43
5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
5.2 The Test Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
5.2.1 2D Wave Flume . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
5.2.2 Wave Generation System . . . . . . . . . . . . . . . . . . . . . . . . . . 44
5.2.3 Wave Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
5.2.4 Energy dissipation system . . . . . . . . . . . . . . . . . . . . . . . . . . 48
5.2.5 Data Processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
5.3 Calibration of the wave (cid:29)ume . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
5.4 Experimental Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
Contents vii
5.4.1 Physical characteristics of the studied model . . . . . . . . . . . . . . . . 50
5.4.2 Construction of the physical model . . . . . . . . . . . . . . . . . . . . . 54
5.4.2.1 Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
5.4.2.2 Control of the material characteristics . . . . . . . . . . . . . . 56
5.4.2.3 Construction of the model . . . . . . . . . . . . . . . . . . . . . 59
5.4.2.4 Reconstruction of the model . . . . . . . . . . . . . . . . . . . 61
5.4.2.5 Placement of the sensors . . . . . . . . . . . . . . . . . . . . . 63
5.4.3 Experiments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
5.4.3.1 Realized experiments . . . . . . . . . . . . . . . . . . . . . . . 64
5.4.3.2 Experimental procedure . . . . . . . . . . . . . . . . . . . . . . 65
5.4.4 Procedure to analyse the data . . . . . . . . . . . . . . . . . . . . . . . . 66
5.4.4.1 Separating the incident and re(cid:29)ected waves: LASA V . . . . . 66
5.4.4.2 Analysis of the waves: LPCLAB 1.0. . . . . . . . . . . . . . . . 67
5.4.4.3 Analysis of the re(cid:29)ection coe(cid:30)cient . . . . . . . . . . . . . . . 69
5.4.4.4 Analysis of the damage progression. . . . . . . . . . . . . . . . 70
6 Results 77
6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
6.2 Calibration of the wave (cid:29)ume . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
6.3 Interpretation of the theories calculating the maximum wave height . . . . . . . 80
6.4 Hydraulic stability of the mound breakwater . . . . . . . . . . . . . . . . . . . . 85
6.4.1 Wave re(cid:29)ection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
6.4.1.1 The re(cid:29)ection coe(cid:30)cient in function of kh . . . . . . . . . . . . 85
6.4.1.2 The re(cid:29)ection coe(cid:30)cient in function of Ir . . . . . . . . . . . . 87
6.4.1.3 Comparing with the re(cid:29)ection coe(cid:30)cient in deepwater . . . . . 88
Contents viii
6.4.2 Damage analysis on the armour layer . . . . . . . . . . . . . . . . . . . . 93
6.4.2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
6.4.2.2 Qualitative analysis . . . . . . . . . . . . . . . . . . . . . . . . 93
6.4.2.3 Quantitative analysis . . . . . . . . . . . . . . . . . . . . . . . 96
7 Conclusions 102
A Terminology of the experiments 104
B Wave (cid:29)ume 106
C Working of the AWACS 108
D Seperation of incident and re(cid:29)ected waves 113
E Calculation of the initial porosity 115
F Example of a test report 116
G Test results 119
Bibliography 130
List of Figures
2.1 Mound Breakwater failure modes de(cid:28)ned by Bruun . . . . . . . . . . . . . . . . 10
2.2 The two most important failure modes by mound breakwaters: extraction of
armour elements and heterogeneous packing. The classical view vs. the hetero-
geneous packing view . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
3.1 Face to face (cid:28)tting by cubes reducing the friction with the (cid:28)lter layer . . . . . . 19
3.2 A selection of the existing concrete armour units . . . . . . . . . . . . . . . . . 23
3.3 A new armour element: the Cubipod . . . . . . . . . . . . . . . . . . . . . . . . 28
3.4 Drop test results of Cubipods compared with cubes showing the lost weight . . 30
3.5 Penetration of the Cubipods in the armour layer . . . . . . . . . . . . . . . . . 30
3.6 The separating e(cid:27)ect of the protuberances avoiding the face-to-face arrangement 31
3.7 Example of placement in a depository of Cubipods . . . . . . . . . . . . . . . . 32
3.8 The casting system designed by SATO and the tongs for movement and man-
ufacture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
4.1 Types of breaking waves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
4.2 Distribution of the wave heights by breaking, concerning that all the broken
wave heights will have the breaking wave height in the sur(cid:28)ng zone . . . . . . . 37
4.3 Distribution of the breaking wave heights over the distribution of the unbroken
waves (Goda [46]) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
ix