the morris island lighthouse phase i foundation

The Morris Island Lighthouse Phase I Foundation Stabilization Project

Submittal for Pile Buck International, Inc.

Submitted by: Taylor Bros. Marine Construction Inc. &

WPC Inc.

Morris Island Lighthouse Foundation Stabilization Phase 1 March 23, 2009 Submittal for Pile Buck Article

Taylor Bros. Marine Construction Company & WPC Inc. of 14

CompanyName:TaylorBros.MarineConstruction,Inc.MemberofPDCAChapter:SouthCarolinaChiefExecutiveOfficer:JuliusTaylor,Jr.,PEEntrySubmittedBy:JuliusTaylor,III(TaylorBros.Marine)&JoshAdams(WPCInc.)CompanyName:TaylorBros.MarineConstruction,Inc.Address: Taylor Bros. Marine Construction, Inc.

135 Oak Road

City:Beaufort State:NC Zip:28516WebPage:www.taylorbrothersmarine.comPhone:252‐728‐2525Mobile:910‐622‐3770Email:[email protected],[email protected]:MorrisIslandLighthouseFoundationStabilizationPhaseIProjectOwner:U.S.ArmyCorpsofEngineersProjectStartDate:April20,2007 CompletionDate:March28,2008



PROJECTSUMMARYThe Morris Island Lighthouse is an iconic, historic structure in Charleston, SC. Sinceconstructionofthelighthousewascompletedin1876,ithasenduredten(10)hurricanesofClass Iorgreater, the1886Charlestonearthquake, andbombingat theendofnearbyFolly Beach during World War II. However, construction of jetties at the entrance ofCharlestonHarbor to improve shipping access from1878 to1896 started the erosionofMorrisIsland.Inthe1890’s,thelighthousewasapproximately2,700ftfromtheshoreline(Figure1a).By1938,theshorelinewasatthelighthouse(Figure1b)andtheexposureofitsfoundationtotheAtlanticOceanbegan.

(a)circa18761 (b)circa19382 (c)5/20073Figure1.SelectedMorrisIslandLighthousePhotographswithTime.

Theexposureofthelighthousefoundationtotheoceanhasledtothedeteriorationoftheunderlying timber piles and timbermatting on which the structure is founded. A steelsheetpilecofferdamwasinstalledaroundthelighthousein1939toprotectthelighthousefoundation.However,overtheyears,thosesheetpileshavecorrodedawayabovethemudline,onceagainexposingthelighthousefoundation.Overtime,thetimberpilesunderthelighthouse have become severely degraded, compromising the foundation integrity andmovingthelighthousetowardscollapse.InordertoprotectandstabilizetheMorrisIslandLighthouse from further damage, a steel sheet pile cofferdam was designed by the U.S.ArmyCorpsofEngineers.Thisdesignconsistedofringof46ftlongPZ‐40sheetpileswithadiameterof72ftandaprotectiveriprapbarrier.ThenewPZ‐40sheetingwasinstalledwithin6ftoftheexistinglighthousefoundation.This project showcases the following: that driven piles can be installed in hazardousmarine conditions safely and effectively; how collaboration between a pile drivingcontractor and an engineering firm dispelled themyth that installation of sheetingwithvibratoryhammers in sandsdamage adjacent structures; and thatdriven sheetpiles arenoweffectivelyprotectingahistoriclighthouseinCharleston,SC.1Photographcourtesyofhttp://www.uscg.mil/hq/g‐cp/history/WEBLIGHTHOUSES/LHSC.html.2 Photograph courtesy of savethelight.org. 3 Figure taken by WPC personnel.



MEETINGTHECHALLENGEOFADIFFICULTJOB:Currently,thelighthouseisapproximately1,600ftfromtheshoreline(Figure1c).Figure2presents the shorelines in 1854 and 1979 relative to the lighthouse in plan view. TheexposureofthelighthousefoundationtotheAtlanticOceanhadseverelydeterioratedthetimbercomponents(i.e.timberpilesandtimbermatting)ofthelighthousefoundation,asshowninFigure3.

Figure2.MorrisIslandShorelinesrelativetoCharlestonHarborJetties(Courtesyofhttp://www.wcu.edu/coastalhazards/Libros,afterZarillioetal.,1985).

Figure 3. Composite Plan View of Confirmed Missing Timber Piles and Grillage (After Sheridan, 1999; ICC, 2001; and Hajduk et al., 2007).



A total of 136 PZ-40 sheet piles by 46 ft long were installed to create the cofferdam. The steel sheeting required 16 mils (two coats) of coal tar epoxy polyamide on the top 15 feet of each sheet (i.e. to the mud line). Each sheet also had one each 24 pound zinc anode welded to it at the 15 foot paint interface line. The basic design concept is presented in Figure 4. The contract also called for the removal of the concrete debris from the 1939 repair, the installation of a geo-textile filter cloth below the riprap barrier, and the installation of six (6) 12-inch square pre-stressed concrete (PSC) piles to be used as the foundation of a new boat access dock.

Figure 4. Morris Island Lighthouse New Sheet Pile Cofferdam Conceptual Design. ThefollowingchallengessurroundedtheinstallationofthePZ‐40sheetpilingaroundthehistoricstructure:

� Access to the Lighthouse: Access to the lighthouse is difficult due to changes intides, which average 6 ft difference between low and high tides, waves, windconditions,andthedepositionofsandbarsaroundthelighthouse.Figure5showstypicalwaveconditionsaroundtheMorrisIslandLighthouse.

Figure5.TypicalwaveconditionsatMorrisIslandLighthouse.



Ajack‐upbargewasselectedforusetoovercomethetideandwavechallengesandprovidedasteadycraneandworkplatformfortheinstallationofthePZ‐40sheetingandassociatedHPpilingforthetemplate.Thejack‐upbargeispresentedrelativetothelighthouseinFigure6. Accessingthejack‐upbargeviasmallboat,andmovingthejack‐upbargestillremainedproblematicduringhighseadays.

Figure6.Jack‐upBargeatMorrisIslandLighthouse(takenfromtopofLighthouse).

� BuriedObstacles:Remnantsoftheoldlighthousebuildingfoundations,walls,andportionsofthe1939repairwerelocatedaroundthestructure.Allofthisdebriswaslocated belowMean LowTide,with a substantial portion below the existingmudline.Figure7showsafoundationfromtheoldlightkeepersresidencevisibleatlowtide.

Figure7.ExistingDebrisaroundLighthouse.



While some of the debris could be located at low tide, the exact location of themajority of these obstacles was unknown. The debris around the lighthousepreventedthe installationofseveralPZ‐40sheetpiles to therequiredembedmentwith the originally selected vibratory hammer (an APEModel 50). An extensivepile‐probing program, consisting of driving and removing HP piles concentricallyaroundthelighthouse,wasimplementedtodeterminetheextentofthedebrisfieldaround the lighthouse. The results of this pile‐probingprogramare presented inFigure8.Afteranextensiveevaluationofdifferentoptions,suchasremovalofthedebris andexpansionor contractionof the sheetpile cofferdam, thedecisionwasmadetoincreasethesizeofthevibratoryhammertoanAPEModel150andutilizeagravitydrophammeronstubbornpilesand“punch”throughthedebris.Thisoptionwas successfully implemented. TheAPEModel150performedverywell, and thedrophammerwasusedonabout20extrastubbornlocations.AdditionaldetailsofthevariousoptionevaluationsarepresentedintheCostSavingMeasuressectionofthissubmittal.

Figure8.PileProbingProgramResults.

� PotentialDamagetoaHistoricStructure:Giventheproximityofthenewsheetingto the historic lighthouse and the compromised nature of the existing lighthousefoundation, thepossibilityof the sheetpile cofferdam installation causingdamage



wasamajorconcern. Therefore,thespecificationscalledforthedevelopmentofaVibrationControlPlan(VCP)andpre&postconditionsurveysofthestructure.Thepre‐conditionsurveysofthestructureshowedthatthestructurehadextensivecracking throughout and an existing rigid body lean. In addition, computermodelingof the lighthousewasconductedtodetermine itsnatural frequencies. Asystemofdocumentingandcategorizingtheexistingcrackswasdevelopedandtheexistingleanmeasured.AnexampleoftheexistingcracksispresentedinFigure9,whileFigure10presentsacompilationofleanmeasurementsinplanviewthroughtheyears.

Figure9.DocumentedExistingInteriorCracksfortheMorrisIslandLighthouse.



Figure10.ExistingLeanMeasurements(PlanView).

Based on the pre‐condition survey results, computer modeling, analysis oflighthouseexistingdocumentation,andvibrationanalysisusingdatafromthePDCADrivenPileGroundVibrationCaseHistoryDatabase,anextensive instrumentationplan was developed that would monitor the lighthouse during all constructionactivities, to includedrivenpile installation. The instrumentationwouldmeasurestructuretilt,existingcrackmovement,vibrations,andenvironmentalfactorssuchastemperature,windspeedanddirection,etc.Thismonitoringdatawasplacedona website to be viewed by all interested parties. Figure 11 shows the datamonitoringwebsite.



Figure11.MorrisIslandLighthouseDataMonitoringWebsite.DESCRIPTIONOFPILETYPESANDUTILIZATION:Thefollowingdrivenpileswereusedforthisproject:

� 72ftDiameterSheetPileCofferdam:PZ‐40by46ftlongwith16 mils (two coats) of coal tar epoxy polyamide on the top 15 feet of each sheet (i.e. to the mud line).

� TemplatePiling:HP12x53steelpileswithlengthsfrom30ftto40ft.� TemporaryDockPiling:Two(2)12¾inchODby0.313W.T.by25ftlongOpen

EndedPipe(OEP)Piles� PermanentDockPiling:Six(6)12‐inchsquarePre‐StressedConcrete(PSC)pilesx

46ftlong.INNOVATIONINCONSTRUCTIONTECHNIQUESORMATERIAL:Thisprojectinvolvedupgradingaprovensolution(i.e.cofferdamswithsteelsheetpiling)withcurrentcorrosionprotectiontechniques(sacrificialanodes,protectivecoating,andarip‐rapbarrierwithunderlyinggeotextiles).The1939sheetpilerepairiswidelycreditedwith saving theMorris Island Lighthouse. However, it was not designed to account fordecadesofcorrosionandsubsequentlyfailed. ThecurrentcofferdamdesignaccountsforthisoversightandshouldprotecttheMorrisIslandLighthousefordecadestocome.UNIQUEAPPLICATIONOFPILESORDESIGNCONSIDERATIONS:



This project, which is essentially the installation of large sheet piling with a vibratoryhammer in loose, poorly graded sands directly next to a historic structure with acompromised foundation, couldbe conceivedby thosewithoutproper knowledge as theworse case application for driven piles. Critics against driven piles stated that thisapplication of sheet piling installedwith a vibratory hammerwould generate vibrationsthat would settle the nearby sands and/or resonate the historic structure, causingirreparable damage. However, the use of engineering knowledge, specifically the datawithinthePDCADrivenPileCaseHistoryDatabase,andanextensivemonitoringprogramshowedthatvibrationsgeneratedfromvibratoryhammerdrivensheetpilingnearhistoricstructures can be managed. The monitoring plan showed that while the Lighthousemovedoverthecourseoftheproject,thesemovementsdidnotcorrelatetodrivenpilevibrationsandthatthecompletionofthesheetpilecofferdamstoppedthelighthousemovement.Inessences,thesheetpilecofferdamprotectionstartedworkingimmediately.CONSTRUCTIONPROBLEMSANDSOLUTIONS:As stated in theMeeting the Challenge of a Difficult Job section of this submittal, theprojectmetwiththreemajorconstructionproblems.Thefollowingisasummaryoftheseproblemsandtheirsolutions.AccesstotheLighthouse:Solvedbytheuseofajack‐upbarge.Buried Obstacles: Solved by the use of a bigger vibratory hammer combined with aconventional drop hammer to “punch” through debris following debris mapping and adetailed analysis of various options. Additional details are provided in the in the CostSavingMeasuressectionofthissubmittal.PotentialDamagetoaHistoricStructure:Solvedbyconductinganexhaustiveanalysisofthe structure and the effects of potential ground vibrations generated during the pilinginstallations. ThedatafromthePDCADrivenPileCaseHistoryDatabasewasusedinthisanalysis. Figure12presentsthepredictedvibrationswithdistancefortheAPEModel50vibratoryhammer.AlsopresentedinFigure12arevariousvibrationcriteria,thedistancefromthenewPZ‐40sheetpilingtotheold1939sheetpiling,andthedistancefromthenewPZ‐40sheetpilingtothelighthousefoundation.



Figure12.PredictedvibrationsfromAPEModel50VibratoryHammer(developedusing

PDCADrivenPileCaseHistoryDatabase).COSTSAVINGMEASURES:After obstructions were encountered during PZ‐40 installation with the APE Model 50vibratory hammer that prevented the sheet piling from being installed to the requiredembedment depth, the pile probing program previously describedwas implemented. Itshouldbenoted that theseobstructionswerenotaddressed in theprojectspecifications.Afterthecompletionofthisprobingprogram,severaloptionswereevaluatedtofinishtheproject. Data used to evaluate each option included: vibration estimates, pre‐conditionsurveyresults,computermodelingresults,andthemonitoringdatauptothatpointintime.Thefollowingisabriefsummaryoftheevaluatedoptions:

� LargerDiameterCofferdamWall.Thisoptionwouldsignificantlyincreaseprojectcostsfromadditionalsheetingandinstallationandstillwouldencounterdebris(asshown in the probing plan in Figure 8. In addition, the project timeframewouldhavetobeincreased.

� ShorterDiameterCofferdamWall. Thisoptionwouldplace thePZ‐40sheetpilingnexttothe1939repairsheetpiling.Whilethiswouldreducethenumberofsheetsand thereforeproject costs, theengineeringanalysis showed that the remnantsofthe 1939 sheet piling were most likely significantly assisting in supporting thelighthouse compromised foundation. Therefore, itwas decided to not potentiallyjeopardizethelighthousebydecreasingthecofferdamdiameter.



� Cut Off Piles at Refusal. This option would provide poor protection for the

lighthouseandpotentiallyplacetheintegrityofthecofferdamatrisk.

� ExcavateandRemoveDebris. Thisoption couldpotentially exposemoreof theexistinglighthousefoundationtotheAtlanticOceanaswellasundermineit.

� AttempttoDriveThroughDebris.Afterdetailedvibrationanalysisusingthedatacollected from themonitoringprogram, itwasdetermined that a larger vibratoryhammer (APE Model 150) could punch through the debris without generatingharmfulvibrations.Thisoptionwaschosenandsuccessfullyimplemented.

The engineering evaluation of the various options showed that driving with a largerhammerandkeepingtheoriginaldesignwasthecost‐effectiveoptionforthisproject.SENSITIVITYTOTHEENVIRONMENT:Aspreviously described, theMorris IslandLighthouse is awell‐knownhistoric structurelocatedneartheentrancetoCharlestonHarbor.Overtheyears,thelighthousehasbecomeiconic to Charleston. The inability to replace this structure was noted in the projectspecifications,whichrequiredthedevelopmentofadetailedVibrationControlPlanaswellaspreandpostconditionsurveys.Inaddition,theprojectwaslocatedneartheentrancetooneof thebusiestseaportsontheU.S.Easternseaboard. Therefore,additionalrulesandregulationsrelatingtoconstructionnearshippinglaneshadtobefollowed.IMPLEMENTATIONOFSAFETYINITIATIVES:Safetywasof theupmost concern for thisproject, given thedifficultworking conditions.Therefore, a rigorous project safety programwas developed that exceeded theUSArmyCorpofEngineerssafetyrequirements. Despiteworkinginanextremelychallengingandhazardous environment, Taylor Bros. Marine received a U.S. Army Corps of EngineersContractor’sSafetyAwardfortheproject.BENEFITSTOTHEPUBLICOROWNER:Asshowninthestructuremonitoringdataoverthecourseoftheproject,theinstallationof the sheet pile cofferdam provided immediate protection to the lighthouse. Inaddition,theinstallationofthePZ‐40sheeting,associatedtemplatepiling,andvariousdockpilingdidnotdamagethestructure.Thiswasverifiedbythepost‐conditionsurvey,whichshowed no significant damage to historic lighthouse occurred during the project. Anexample of the protection provided is presented in Figure 13, which shows a wavebreakingonthesheetpilecofferdam.ThenewPZ‐40 steel sheetpile cofferdamprovides thehistoricMorris IslandLighthousewith the protection is needs from the Atlantic Ocean, allowing future foundationstabilizationandrenovationworkandforfuturegenerationstoenjoyitsbeauty.



Figure13.WavesbreakingovertheMorrisIslandLighthouseSheetPileCofferdam.DrivenPilesProtectingthePast,HelpingPreservetheFuture.

the morris island lighthouse phase i foundation

Documents