Pre-piling - NGI

Geo-Engineering gatheringOffshore EnergySubsea MetrologyThe key for pre-piled offshorefoundations

Pre-piling - Sequential mass installationPre-installation of Piles using mobile piling template (GeoSea)Transit of jackets or tripodsLifting/stabbing the structuresinto pre-piled foundationsTopside completion

Pre-piling…How to make it fit?Illustration from OWEC Tower ASTypical Installation Tolerances:• Driving piles with max 200mmdifference in elevation & max 1° tilt• Horizontal positions given by tolerancesin piles guides on template• ”As driven” pile top elevations measuredwith better than 10mm accuracy

”Smart” Piling TemplatesQuattro pod jackets (OWEC)Tripods (OWT)

Critical operations – Monitoring controlFiberOpticGyroBiaxialinclinometer

Instrumentation of a piling framePrecision in Rough conditionsNo pile drivingPile drivingSensor endurance during driving

Did it work?2009 Alpha Ventus - 6 off OWEC Quattropods installed by Norwind/GeoSea2010 Ormonde - 42 off OWEC Quattropods installed by GeoSea2011 Thornton - 49 off OWEC Quattropods installed by GeoSea2011 Borkum West - 41 off OWT Tripods installed by GeoSeaPresently 511 pre-piled piles have been installed all inside the tight tolerances.NGI have been responsible for pile driving monitoring and “As installed”metrology. Today all monitoring systems are remote operated without anyROV/Diver subsea intervention required.

Caisson foundations for OWT’sMonitoring control during installation – Vertical but OK?For pre-piled quattropod foundationsthe leveling tolerances are +/-10mmDistorted base mayintroduce significantstress in structuralmembers

Caisson foundations for OWT’sMonitoring control during installationStatoil’sSleipner T jacket2.0Suction penetration phasePenetration depth (m)2.53.03.54.04.55.0Ø 15m “Buckets”0 20 40 60 80 100Suction pressure (kPa)-60 -40 -20 0 20 40 60Elevation differencebetween suction piles (mm)

An extreme event on tape!Long term Performance monitoringDraupnerFirst Jacket without piles heavily instrumentedfor design verificationDraupner platforms

New Year’s Eveat the Draupner platform 1995

The ”Big Bang” recordingsWave impact like a Sledge hammerWave height (m)20151050-5-10Accelerometeron DeckAcceleration in wave direction (m/s 2 )0.50.40.30.20.10-0.1-0,2-0.3-0.4-0.5Deck impactFoundation response0 5 0 1 0 0 1 5 0 2 0 0 2 5 0 3 0 0 3 5 0 4 0 0Accelerometeron Foundation

The ”Big Bang” recordingsFoundation Response20Wave height (m)151050-5-10Monster waveDifferential water pressure (kPa)100806040200-20-40-60-80-100Over pressure (Toe foundation)Suction (Heel foundation)0 5 0 1 0 0 1 5 0 2 0 0 2 5 0 3 0 0 3 5 0 4 0 015MN18MN

Thank you for your attention !