7212019 Breakwater Stability With Damaged Single Layer Armour Units Rover Et Al

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BREAKWATERBREAKWATERBREAKWATERBREAKWATERSTABILITYWITHDAMAGEDSINGLELAYERARMOURUNITSSTABILITYWITHDAMAGEDSINGLELAYERARMOURUNITSSTABILITYWITHDAMAGEDSINGLELAYERARMOURUNITSSTABILITYWITHDAMAGEDSINGLELAYERARMOURUNITS

RicharddeRoverDeltaMarineConsultantsrderoverdmcnlHenkJanVerhagenDelftUniversityofTechnologyhjverhagentudelftnlArnoudvandenBergeDeltaMarineConsultantsavandenbergedmcnl

BasReedijkDeltaMarineConsultantsbreedijkdmcnl

INTRODUCTIONAtbreakwaterandseawallprojectsatPortStFrancisandScarborough breakageofsingle layer armour unitswasobservedItisgenerallyassumedthatbreakageofsinglelayerarmourunitshasasignificantnegativeeffectonthehydraulic stability of a rubble mound breakwater Thesignificantdecreaseofinterlockingcapacityandmassofthe broken units would lead to displacement of theseunits and surrounding units The broken parts of thedamaged units would act like projectiles The waveswould ldquothrowrdquo thesebroken partsback and forth tothearmour layer More armour unitsmay breakdue to theimpact of these broken parts leading to rapid damageprogressionofthearmourlayerandfinallytofailureofthe

total construction Thisdamage behaviourhashoweverneverbeenconfirmedOBJECTIVEThemain objective ofthisresearch isto determine theeffect of single layer armour unit breakage on thehydraulic armour layer stability and potential damageprogressionPHYSICALMODELA 2-dimensional model of a rubble mound breakwaterwithatypicalcrosssectionistestedinawaveflumeatDelftUniversityofTechnologyThearmourlayerconsistsofmodelXblocarmourunitswithanominaldiameterDnof277cmandadesignwaveheightHdof10cm

Figure1ndashclusterofbrokenXblocarmourunits(inred)FromeverymodelXbloc unitthatsimulatesa damaged

unitonenoseorlegiscutoffThedetachednoseorlegisglued back on the unit with a sugarwater solution toplace the units in the armour layer When exposed towater the sugar dissolves again simulating the brokenunitsinrealityascloseaspossibleTESTINGSET-UPIrregularwaveswithaJonswap-spectrumareusedduringthetestseriesThewaveheightisincreasedfrom80uptill 190ofthedesignwaveheight ata constant waterdepthof055mandawavesteepnessof0045Different

configurationswithbrokenunitsaretested075or15oftheunitsaroundstillwaterleveloveraheightof2HdarebrokenThedamagedunitsareplacedinclustersof 5 units or individual Their position is varied withrespecttothestillwaterlineEXPERIMENTALRESULTSFor all test series with broken units start of damageoccurredat significant lowerwave heights compared toan armour layer with no broken units However failureoccurredatapproximatelythesamewaveheightsasforan armour layer with no broken units Increasing thepercentageofbrokenunitsornumberofbrokenunitsinaclusterhadonlyaminoradditionalnegativeeffectonstart

ofdamageandfailureThepositionofthedamagedunitsaround the stillwater line overaheight of2Hdgavenodifference in influence of the broken units on start ofdamageandfailureThemajorityofthedetachednosesandlegsshowedlittletonomovementandstayedinthearmour layeror even tend todigthemselvesin the firstunderlayerCONCLUSIONS

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Figure2ndashgeneraldamagebehaviourfordifferenttypesofarmourlayer

The damage progression of an armour layer withdamaged units is long and gradual compared to thedamageprogressionofanarmourlayerwithnodamagedarmourunitsThistypeofdamageprogressionlookslikethedamageprogressionofanarmourlayerconsistingofrip-raprockOnlyafewbrokennosesand legsshoweddisplacementduring the test series Itis therefore unlikelythatunderinfluence of the waves the broken parts will act asprojectilesdamagingotherunits