ENERGIES MARINES RENOUVELABLES: Géotechnique & FondationsHong DOAN & Denys BORELRencontre des partenaires WeAMEC du 7 avril 2017

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Ground model - Making the Development Site Transparent

Desk top study Geophysical Surveys Insitu Testing (CPT)

Boreholes sampling & testing Lab Testing and Analysis Interpretation and IntegrationEngineering Ground Model

Engineering Analysis and Design Optimised design

Starting Point

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Ground model - Multi-Disciplinary Integration

Ground Model

Public Domain

Analogous Sites/Previous ExperienceGeotechnical Data

Documents understanding of site geological evolution

GIS Database

Metocean

Geophysical Data

Engineering Analysis

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Ground model approach

Seabed Features

Sand/gravel bedforms Boulders

at seabed

Uneven seabed

Exposed bedrock

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Variablesoil conditionse.g. channels

Variable bedrockprofileCoarse

materialincludingboulders Competent

stratae.g. evaporites

Subsurface Features

Weatheredzone

Ground model approach

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Ground model approach

Mobileseabed /

scour

Obstruction to caisson

Variablepenetrationfor different

piles

Shallow refusal

Bucklingof pile

Foundation Constraints

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Foundation Constraints Register

� Documents potential constraints to foundation installation / behaviour

� Ground Model is used in order to identify, map, characterise and predict ground conditions

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How?

1. Geophysical survey2. Soil investigation

• drilling & sampling / coring• in-situ testing

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How? Examples – UXO survey

ROV video footage confirms the geophysical interpretation

Seabed Features

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How? Soil investigation: Basic Principle

High quality sampling & in situ testingrequire a fixed reference / seabed

From a jack-up rig(self elevating platform)

From a floating support

Boreholefrom a vessel / barge

with heavecompensated

drillstring +

seabed frame

wireline seabed

modules & equipmentsfor

In situ testing or

sampling

~ conventional borehole

with casing betweenplatform deck

and seabed

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How? Soil investigation: Operations modes

Seabed based

Downhole in drill pipe

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How? Soil investigation: New seabed systems drilling & testing

Seafloor Drilling Technology

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How? Soil investigation: Laboratory for Advanced Testing

� Fugro laboratory for advanced soil testing located in UK + France

� Advanced equipment for cyclic and dynamic testing� 32 automated stress-path systems� 10 cyclic simple shear systems (DSS)� 10 cyclic triaxial systems (up to 300mm in sample diameter )� 3 resonant column apparatuses� Bender element capability in triaxial cells and DSS/CSS� Axial and radial small-strain measurement capability� Mid-height pore pressure capability

� Accredited for soil testing by UKAS to ISO 17025

Fugro laboratory for advanced soil testing

Fugro automated stress path triaxial systems

Fugro cyclic simple shear (DSS) sample cell

Fugro sample for triaxial testing with axial and radial strain measurement

Design of Offshore Foundations for Wind Turbines

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French Marine Energy Market - Fixed Offshore Wind

AO1 Saint Brieuc

AO1 Courseulles

AO1 Fécamp

AO1 Saint Nazaire

AO2 Yeu Noirmoutier

AO2 Dieppe Le Treport

AO3 Dunkerque

AO3 Ile d’Oléron

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French Marine Energy Market - Floating Offshore Wind

Leucate

Gruissan

Faraman

Provence Grand Large

Groix

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TIDAL energy

WAC: Wave Energy Converters :

OTEC: Ocean Thermal Energy Converter

French Marine Energy Market

Other Energies

Image: ©DCNS

Image: ©DCNS

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Site characterisation for offshore Windfarm Development

Feasibility and licence application Consent and FEED studies Detailed design and

procurement Construction and commissioning

2011 Phase 1 geotechnical investigation

Foundationconcept

2011 DTSPreliminary

ground model

2013 Phase 2 geotechnical investigation

De-risking+

Foundationconcept

validation

2015 Phase 3 geotechnicalinvestigation

+ advanced labtesting

Final groundmodel for

Foundationdesign

2013 Export cable

investigation

Burialassessment

Andcable landing

2013 Inter array cable

investigation

Burialassessment

+Cable

Micro routing

2016Onshore large scale

pile tests & engineering study

to confirm:

Driveability in rock

Behaviour of monopile in

rock

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General Considerations

� Must be cost-efficient

� Strict guidelines for certification (e.g. DNV-GL, LR) and approval authority BSH (for German projects)

� Natural frequency fn should not be close to excitation frequencies to avoid resonance (Natural Frequency Analysis NFA and Fatigue Limit State FLS)

� Safety against failure in the Ultimate Limit State (ULS)

Consideration of extreme loads (50-year wave and wind forces – BSH storm load)

� Meet Serviceability Limit State (SLS) requirements

Must consider the effects of long-term cyclic loading (from wind and wave loads)

� Installation and de-installation

Offshore WTG Design – Geotechnical Requirements

Typical WTG Cost Distribution (Kuehn et al., 1998)

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Monopile Design – Geotechnical Requirements

Design Considerations

– Natural frequency (FLS and NFA) decisive for design

• Soil-structure stiffness response for relevant load range (dynamic, low-amplitude)

– DNV-GL, BSH requirement:

• Effects of cyclic loading shall be explicitly considered in ULS and SLS design (as a function of number of cycles and load amplitudes)

– Limitation of pile lateral displacement (SLS)

• Rotation at seabed level for lifetime duration < 0.25°

– ULS verification should consider design 50-year storm load case• BSH 35-hour cyclic storm load case

– Installation through pile driving

• Large-diameter/thin-walled piles more prone to buckling and damage (e.g. installation in very dense sand or glacial till)

www.lorc.e-kvator.com

Monopile Foundation

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Jacket Design – Geotechnical Requirements

Design Considerations

– Axial cyclic tension resistance – driving factor for design of piles

– DNV-GL, BSH, DIN 1054 requirement:Effects of cyclic loading shall be considered in ULS and SLS design

Fugro Procedure

– Automatised software CYCLOPS

– Cycle-by-cycle analysis of axial displacement accumulation

– Provides site-specific cyclic t-z (shaft friction-axial displacement) curves

Dong et al. (2012)

Tripile and Jacket Foundations

Pile resistance forces to tension loading (Achmus & Müller , 2010)

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Gravity Base – Geotechnical Requirements

Information on this slide is confidential and shall not be communicated without Fugro’s permission

Gravity Foundations

Design Considerations

– Combined VHMT loading : torsional forces can reduce bearing capacity

- Effects of consolidation (strength increase) on stability

– Reduction of soil strength and stiffness due to cyclic loading (ULS, SLS)

– Typical requirement δ < 0.25°to 0.5°

– SLS verification needs to consider:• Consolidation and creep• Post-strorm reconsolidation settlement• Shear-induced deformation• Lateral variability

– Scour protection , seabed preparation and/or skirts normally required

Weight

Thornton Bank OWF

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Suction Bucket – Geotechnical Requirements

Design Considerations

Capacity:- Effects of cyclic degradation - Capacity under compressive, tension and prolonged

tension

Displacement:- Effects of cyclic degradation- SLS verification needs to consider

- Consolidation and creep- Lateral variability- Shear-induced deformation

Installation:- Is suction (water pressure) sufficient during

installation? Can the bucket penetrate to required depth? Risk of plug uplift?

Suction Buckets/Multi-Pod Foundations

SPT (2014)

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Fugro Methodology for Cyclic Bearing Capacity Analysis

CLR = 1 (1-way loading)

CLR = >>1 (2-way loading)

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Floating Offshore Wind – Anchor Design Process

Client specifies Client and/or Fugro• Mooring / metocean conditions• Type of mooring system• Type of moored object

Permanent (FPSO, FSO, FPI)Temporary (MODU, barge, etc)

• Mooring line characteristics• Anchor loads (quasi-static / dynamic)

intact / damaged / transient• Specifications and applicable codes

LocationSite conditionsBathymetryGeophysical data / Geohazards /Geological data / Geotechnical data

Suitable anchor

Anchor sizingAnchor performanceInstallation requirementsLong term behaviour (creep, consolidation, cyclic…)

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Floating Offshore Wind – Anchor Types

ACTIVITY IN R&D

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R&D projects

SOLCYP : French acronym for Piles under Cyclic SOLicitationsLeading by Fugro, Dr Alain PUECH

CITEPH :Gassy soils, Laboratory testing and numerical modelingARSCOP: High pressure pressiometer

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SOLCYP OBJECTIVES

SOLCYP’s Objectives:

� understand the physical phenomena conditioning the response of piles subject to vertical and lateral cyclic loads

� quantify the effect of cyclic loadings on the response and capacity of piles

� define a methodology to assess the behaviour of cyclically loaded piles

� develop design methods sufficiently flexible in use to remain compatible with the nature of the structure and the severity of the cyclic loading

� initiate prenormative actions with a view of introducing the proposed methodology in national (and international) codes or professional guidelines

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SOLCYP - Response of soil-pile system under axial loading (1)

Extensive experimental database gathered from:

� In situ tests in two experimental sites : Merville (stiff to very stiff over-consolidated clay) and Loon-Plage (dense to vey dense fine sand)

� Centrifuge tests in IFSTTAR (formerly LCPC) : model pile tests in Fontainebleau sand

� Calibration chamber in 3S-R laboratory and in collaboration with Imperial College : highly instrumented pile in Fontainebleau sand

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SOLCYP - Response of soil-pile system under lateral loading (2)

Experimental P-y curves :� y(z) : Displacement obtained by double-integration the moment data� P(z) : Soil Reaction obtained through double derivation of the moment data

Typical P- y curve in clay Typical P- y curves in sand

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SOLCYP - Response of soil-pile system under lateral loading (2)

Global analyses Local (beam column) analysesDerive degredation laws dependingon cyclic loading parameters for : - Pile head displacement (yn)- Maximum Bending Moment (Mmax,n)

Derive degraded P-y curves from static “standard” P-y curves

Pile design under lateral cyclic loading

Thank you