Geotechnical Challenges in Offshore Engineering BE in Civil Engineering (UCD 2005) Dr. David Igoe PhD in Offshore Pile Design (UCD 2009) Delivering the most progressive, reliable, and efficient Postdoctoral Researcher (UCD 2010 – 2015) BE PhD CEng MIEI Head of Offshore at GDG (2016 – Present) geotechnical designs across a wide variety of situations. Engineers Ireland / ICE Presentation 2017 – David Igoe
Overview Introduction Key Geotechnical Challenges Monopiles Jacket Structures Gravity Base Foundations Research Projects PISA (Pile Stability Analysis) Pile Ageing DemoGravi3 Other Projects Conclusions Engineers Ireland / ICE Presentation 2017 – David Igoe
Introduction Engineers Ireland / ICE Presentation 2017 – David Igoe
Offshore Wind Engineers Ireland / ICE Presentation 2017 – David Igoe
Offshore Wind European Offshore Wind Installations up to 2015 (EWEA) Engineers Ireland / ICE Presentation 2017 – David Igoe
Offshore Wind Economics Pre 2015, average price >€100 / MWh July 2016 - Borssele 1&2 wind won at €72 per MWh (Dong Energy) Oct 2016 - Kriegers Flak won at €60 per MWh (Vattenfall) Dec 2016 – Borssele 3&4 won at €54.5 / MWh (Van Oord / Shell) March 2017 - Engineers Ireland / ICE Presentation 2017 – David Igoe
Offshore Wind Economics Pre 2015, average price >€100 / MWh July 2016 - Borssele 1&2 wind won at €72 per MWh (Dong Energy) Oct 2016 - Kriegers Flak won at €60 per MWh (Vattenfall) Dec 2016 – Borssele 3&4 won at €54.5 / MWh March 2017 – First Subsidy-free offshore wind bid – Dong Energy Engineers Ireland / ICE Presentation 2017 – David Igoe
Offshore Wind – Geotechnical Engineering Challenges Foundation Design Monopiles Lateral Loading Cyclic Loading Tripods / Jacket Structures Pile Axial Loading Ageing Cyclic Loading Gravity Base Shallow Foundations Cyclic Loading Engineers Ireland / ICE Presentation 2017 – David Igoe
Offshore Wind – Geotechnical Engineering Challenges Foundation Design Monopiles Lateral Loading Cyclic Loading Tripods / Jacket Structures Pile Axial Loading Ageing Cyclic Loading Gravity Base Shallow Foundations Cyclic Loading Engineers Ireland / ICE Presentation 2017 – David Igoe
Monopile Design Traditional Monopile Design Lateral Pile Response typically using 1D FE ‘p - y’ approach Engineers Ireland / ICE Presentation 2017 – David Igoe
Monopile Design Traditional Monopile Design Lateral Pile Response typically using 1D FE ‘p - y’ approach API ‘p - y’ curves derived from small diameter (0.6m diameter), slender pile tests – Not suitable for monopiles typically >4m API approach thought to be conservative for monopiles Implemented in 1D FE model software (e.g. LPile / Oasys ALP) Engineers Ireland / ICE Presentation 2017 – David Igoe
Offshore Wind – Geotechnical Engineering Challenges Engineers Ireland / ICE Presentation 2017 – David Igoe
Monopile Design - ULS Monopile Design – ULS case When large extreme load hits structure - Structural and Soil Integrity Checks. Including scour corrosion and cyclic degradation due the environmental and turbine loading. Ensure deflection/rotation does not become excessive (<2 degrees) Pile Length Check – Change in length should not significantly effect mudline rotation – 10% criteria Engineers Ireland / ICE Presentation 2017 – David Igoe
Monopile Design - SLS Monopile Design – SLS case Ensure permanent accumulated rotation due to cyclic loading does not exceed specified tolerance – typically 0.5 degrees Hettler approach Values of t and Neq are calculated from rainflow counting of a BSH storm event 0.16 < t < 0.22 (Seed et al.) Neq typically <15 Engineers Ireland / ICE Presentation 2017 – David Igoe
Monopile Design – FLS & DLS Monopile Design – FLS & DLS case Structural fatigue checks - Materials within structure to last beyond specified design life. Fatigue check performed using linearized ‘p - y’ springs Should include driveability analysis – Stresses and blowcounts from driveability analysis used in structural fatigue checks Dynamic check to ensure natural frequency of structure lies outside excitation frequency bands to avoid resonance. Engineers Ireland / ICE Presentation 2017 – David Igoe
Monopile Research – PISA project PISA Overview Led by Dong Energy and funded through the Carbon Trust Offshore Wind Accelerator program Academic Work Group involving Oxford, Imperial College and UCD Total Budget ≈ £3m over 2.5 years. Started in August 2013 Project aim was to develop a new design methodology for laterally loaded piles for the offshore wind industry Two Pronged Approach Campaign of Monopile field tests 3D FE modelling of field tests and parametric study Engineers Ireland / ICE Presentation 2017 – David Igoe
Monopile Research – PISA project PISA Overview Field testing began with pile installation in October 2014. Final load testing completed 24th July 2015. Two test sites with 14 pile tests performed at each site DM6 DM7 DL1 DM5 12m DM4 DR1 DM9 21m DS1-4 DM3 DM2 DM1 DL2 Engineers Ireland / ICE Presentation 2017 – David Igoe
Monopile Research – PISA project RAMSTROKE LOAD CELL - LCL STICK UP INCLINOMETERS - SUI DISPLACEMENT M/H TRANSDUCERS - LVDT AH PH AL PL z EXTENSOMETERS - IPE INCLINOMETERS - IPI L FIBRE OPTICS - FOS PIEZOMETERS - PZT D Engineers Ireland / ICE Presentation 2017 – David Igoe
Monopile Research – PISA project Engineers Ireland / ICE Presentation 2017 – David Igoe
Monopile Research – PISA project Engineers Ireland / ICE Presentation 2017 – David Igoe
Monopile Research – Blessington Tests Blessington Monopile Research 15 Piles - Lateral Static Load Tests 3 Piles - Lateral Cyclic Tests Engineers Ireland / ICE Presentation 2017 – David Igoe
Monopile Research – RWE Vibro Tests Other Monopile Research RWE Vibro Project 5 x 4.5m Diameter Pile Tests Comparison between vibrated and impact driven installation Vibrated Installation can: Reduce time of installation Reduce noise and environmental impact to sealife Reduce Cost Engineers Ireland / ICE Presentation 2017 – David Igoe
Monopile Design Optimisation - GDG Engineers Ireland / ICE Presentation 2017 – David Igoe
Offshore Wind – Geotechnical Engineering Challenges Foundation Design Monopiles Lateral Loading Cyclic Loading Tripods / Jacket Structures Pile Axial Loading Pile Ageing Gravity Base Shallow Foundations Cyclic Loading Engineers Ireland / ICE Presentation 2017 – David Igoe
Tripods / Jacket structures – Pile Axial Loading and Ageing Axial Pile Design Jacket structures reasonably well known – challenge for design optimisation Jackets piles primarily resist overturning moments through ‘push - pull’ (tension and compression) axial loading API main text approach uses traditional earth pressure (Beta) approach in sands and total stress (alpha) approach in clays for estimating shaft friction. Database research indicate CPT based method preferable (ICP, UWA, NGI, Fugro) – offer better reliability and more optimised design ICP, UWA, NGI, Fugro methods included in API design guide commentary section and are in theory preferred method ICP method has been used by shell UK for the past 10 years Engineers Ireland / ICE Presentation 2017 – David Igoe
Tripods / Jacket structures – Pile Axial Loading and Ageing 3 Normalised Capacity, Q/Q ICP Pile Ageing 2.5 ICP Intact Ageing Characteristic Primary item of debate in various parts of the 2 offshore engineering community (OTC, API/ISO Blessington 1.5 meetings, ISFOG 2015) Dunkirk 1 EURIPIDES Hound Point 0.5 Padre Island Shaft capacity of piles seen to increase by up to I-880 0 250% over 120 days after installation 1 10 100 1000 Time after Driving (Days) Initial testing performed by Imperial College. Later tests by UWA, UCD and Norwegian Geotechnical Institute (NGI) show similar findings. Engineers Ireland / ICE Presentation 2017 – David Igoe
Tripods / Jacket structures – Pile Axial Loading and Ageing 60 Pile Ageing 50 Required Pile Length (m) In theory, up to 50% on pile length can 40 be saved allowing for 90 days ageing 30 Typically piles are driven first 20 After >30 days jacket structures / Tripods 10 are installed 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 After >90 days Turbines are installed Location No. Max loading will occur a minimum of 90 Pile Required Length (10-days) Pile Required Length (90-days) 70% days after pile installation 60% Huge potential for cost and steel savings 50% Percentage Saving Further Research required for savings to 40% be realised 30% 20% 10% 0% 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Location No. Engineers Ireland / ICE Presentation 2017 – David Igoe
Tripods / Jacket structures – Pile Axial Loading and Ageing Engineers Ireland / ICE Presentation 2017 – David Igoe
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