OSIG

Report
Offshore Site Investigation & Geotechnics Sub-Committee - SUT
Mick Cook - Mick Cook Limited – Chairman
OSIG – Offshore Site Investigation & Geotechnics Committee
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Guidance Notes - Chronology
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Originally commenced 2005
Re-commenced Sept’ 2011
1st draft issued for review Aug’ 2012
Review meeting at TCE Sept’ 2012
Feedback incorporated and document re-structured
Draft 2 issued for comment April 2013
Feedback incorporated
Document finalised and prepared for printing May
2014
 Launch July 14th 2014
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OSIG Renewables Guidance Notes
Sub-committee
NAME
COMPANY
Andy Barwise* 1
Gardline
Will Cleverley* 1
OWC
Mick Cook* 2
Independent Consultant
Ray Hobbs* 1
Independent Consultant
Tony Hodgson* 1
Fugro
Leo James 2
RPS Energy
Chris Jenner 3
Mainstream
Neil Morgan* 1
Lloyds Register
Alastair Muir Wood *1
DONG
Richard Orren* 2
Senergy
Julian Osborne* 1
Vattenfall
Rupert Rowland* 1
Subsea 7
Charles Wark 1
RWE
* = OSIG committee member, 1 = Geotech Eng, 2= Geophysicist, 3 = Environmental Scientist
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Why do we need Guidance Notes?
 Offshore renewables present new challenges
 Offshore SI is a specialist area requiring
specialist input
 Why are these issues important?
– Foundations: ~25-40% of CAPEX
– Cables: ~80% of insurance claims in offshore wind
 Mitigate safety, environmental & commercial
risk
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Examples of offshore renewable sites
•Wind turbine generator
sites
• Hydrokinetic device
sites
•Substation platform
sites
•Cable routes
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Oil & Gas vs Renewables- a question of
scale (?)
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High energy…difficult sites
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Guidance Notes: Objectives
 To provide non-specialists with information on
issues to be considered and practices to be
adopted
 To provide a framework for specialists
 To aid survey planning & execution
 To mitigate safety, environmental and
commercial risks inherent in any offshore project
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Guidance Notes: Guiding Principles
 To aid cost-effective, fit-for-purpose offshore site
investigation (geotechnics and geophysics)
 Sufficiently generic to cover most offshore
renewables developments
 International
 Reference to existing guidelines
 Solely marine/offshore
 Include in-field and export power cables
 Learn from previous guidelines
 Best practice
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OFFSHORE SITE INVESTIGATION AND GEOTECHNICS COMMITTEE
GUIDANCE NOTES FOR THE PLANNING AND EXECUTION
OF GEOPHYSICAL AND GEOTECHNICAL
GROUND INVESTIGATIONS FOR
OFFSHORE RENEWABLE ENERGY DEVELOPMENTS
( May 2014)
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Contents
 Introduction
 Part 1 - Planning
– Managing geological and geotechnical risk
– The ground model
– Planning and offshore ground investigation
 Part 2 - Execution
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General
Geophysical investigation
Geotechnical investigation
Positioning
Data integration, interpretation & reporting
 Glossary
 Appendices
– References, Codes, Standards and Guidance Notes
– Geohazards
– Geotechnical testing methods
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2 Part structure – Planning & Execution
 Part 1 – Planning – this section presents a strategy that
developers are recommended to follow in the planning of
ground investigations and is aimed at practitioners with
minimal experience of geophysical and geotechnical
investigations.
 Part 2 – Execution – this section presents key aspects
that should be considered when performing such ground
investigations. It is aimed at readers actively involved in
the day-to-day management and application of ground
investigations and is designed as an aide-mémoire.
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Managing geological and geotechnical risk – Section 2
 Central to project viability
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Costs
Design
Schedules
Construction methodologies
H&S
Environmental issues
 Reference to Clayton (2001) – why are ground
related risks so high
 Typical hazards
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Hazards and their impact – Appendix 2
Key features to be assessed by means of survey and geotechnical investigations
Man-made features:
• Pipelines: on or buried below the
seabed
• Communications cables
• Wrecks, including ships aircraft &
submarines
• Wellheads and abandoned well
locations
• Unexploded ordnance (UXO) and
related debris, previously deployed or
dumped
• Navigation or metocean buoys
• Archaeological remains
• Miscellaneous debris
• Power and umbilical lines & cables
• Waste, chemical or other dumping
grounds
• Jack-up rig footprints
• Rock dumps
• Scour protection material
• Gravel extraction areas
• Export and intra-array cables
• Wind turbines, wave, tidal arrays
• Manifolds and templates
• Platforms: active, abandoned, or
toppled
• Anchorage
Natural seabed features:
• Seabed topography and relief
• Seabed sediments
• Sand: banks, waves, and mega- ripples
• Glacial features including iceberg plough
marks, flutes and moraines
• Rock outcrops, pinnacles and boulders
• Seabed channels and scours
• Peat
• Gravel beds
• Hard grounds / cemented sands
• Submerged forest or terrestrial palaeolandscape
• Unstable or steep slopes
• Gas vents and pockmarks
• Collapse features
• Fluid expulsion features
• Chemosynthetic communities
• Fault escarpments
• Reefs
• Mud: flows, gullies, volcanoes, lumps,
lobes
• Slumps
• Diapiric structures
• Gas hydrate mounds
Subsurface geological features:
• Sedimentary sequences
• Stratigraphy
• Buried infilled channels
• Hard grounds / cemented sands or
buried land surfaces
• Gravel beds
• Boulder beds
• Rock head or igneous intrusion near
seabed
• Peat
• Erosion and truncation surfaces
• Shallow water flow zones / loose
sands
• Glacial features incl. drumlins, loess
and moraines
• Faults - tectonic or glacigenic
• Shallow gas charged intervals
• Gas chimneys
• Salt or mud diapirs and diatremes
• Buried slumps and mass transport
complexes
• Gas hydrate zones and hydrated soils
Note: The order of significance is likely to depend on the area of the world and the previous experiences of specific environments; surveys are
performed in order to identify what is present – other man made or geological hazards may be present that are not included on this list. A risk and
impact assessment is required to determine whether a hazard present is a risk to development.
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The ground model – Section 3
 Iterative and continuous process throughout life
cycle
 Level of risk inversely proportional to level of
knowledge
 What is a ground model
 Use of the ground model
 Development of the ground model
 Desk study
 Ground investigation programme
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A typical process of understanding
ground conditions – Figure 1
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Example ground investigation process flowchart
for an offshore wind development – Figure 2
Analysis of Regional
Geology
Review the Developer’s
Requirements
Foundation Selection
Shortlisting
Undertake a Desk
Study
Prepare the
Ground Model
Database
Input Data from Section
3.4
Other Surveys
e.g. Metocean,
Environmental,
Archaeological,
etc.
Survey Planning &
Risk Assessment
Reconnaissance
Ground
Investigation &
Testing
Geophysical and
Geotechnical Scope of
Work
Geohazard
Assessment
If required
Factual & Interpretive
Reports
Integrated
Interpretation &
Evaluation
Other Studies
e.g. Foundation
selection/construction,
cabling
Update the
Ground Model
Database
Site Specific Data
Survey Planning &
Risk Assessment
Detailed Ground
Investigation &
Testing
Geophysical and
Geotechnical Scope of
Work
OSIG – Offshore Site Investigation & Geotechnics Committee
Factual & Interpretive
Reports
Update the
Ground Model
Database
Geohazard
Assessment
Site Specific Data
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Example timeline for an offshore wind farm project.
Site investigation phase – Figure 3
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Planning an offshore ground investigation – Section 4
 Aims and objectives
– End users/stakeholders
– Design codes/national standards
 Type of investigation
 Scope of investigation
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Generator and sub-station foundations
Installation and maintenance
Inter-array cables
Export cables
Shore crossings
Data collection structures
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Geophysical vs Geotechnical
Benefits
Limitations
Geophysical Investigations
Wide range of data acquired simultaneously from
one vessel
Large areal coverage in short time – efficiency
Continuity between specific point locations
Wide range of depth of sub-bottom investigation
Remote sensing tool that requires ground
truthing
Qualitative results subject to interpretation
Some systems very weather/noise sensitive
Geotechnical Investigations
Range of systems for different soils and
applications
Quantitative results used for engineering design
Physical measurement of soil and rock properties
Generally, less weather sensitive than geophysics
OSIG – Offshore Site Investigation & Geotechnics Committee
Single data point, may need many locations to
investigate an area
'Slower' acquisition rates than geophysics
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Part 2 – Execution, General – Section 5
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HS&E
Competent personnel
Developer’s representatives
Contractor and vessel/rig selection
Data and information management
– Geospatial data provision
– Standards
 Offshore data processing, analysis and
interpretation
 Developer/contractor liaison
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Geophysical investigation – Section 6
 Reference to other guidance notes
 Equipment used, application, operational issues
and constraints
 Sub-bottom profiling systems
 Time/depth conversion
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Schematic layout of geophysical equipment – Figure 4
Courtesy Osiris Projects
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Geotechnical investigation – Section 7
 Scope of geotechnical works
 Advantages/disadvantages vessel/rig types –
Table 4
 Data coverage – example best practice
geotechnical work scopes for different
foundation types and construction vessels –
Table 5
 Geotechnical data requirements
 Types of sampling and in situ test data – Table 6
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Structure and foundation types – Figure 5
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Positioning – Section 8
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Use of GPS
Reference to existing guidance
Tidal reduction
In-water sensor positioning
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Data integration, interpretation and reporting – Section 9
 Holistic approach
 Integration essential
 Co-ordination over prolonged periods of
investigation
 Limitations
 Report deliverables
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Feedback/comments
Reviewers
Including
British Geological Survey
Certification Authorities/Warranty Surveyors
Bureau Veritas, DnV, GL, Global Maritime,
Intertek, Lloyds Register
China Renewable Energy Engineering Institute
Consultants
Developers
DONG, EDF, E.On, Forewind, GDF Suez,
Iberdrola, Mainstream, Scottish Power, RES, SSE
Renewables, Statoil, Vattenfall
Engineering contractors/consultancies
OSIG
UK, USA, Australia (> 50 members)
Installers
RenewableUK
Survey Contractors
The Crown Estate
Universities
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Acknowledgements and thank you
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RenewableUK
The Crown Estate
China Renewable Energy Engineering Institute
OSIG
OSIG sub-committee
Lloyd’s Register
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Guidance Notes
 Free download from SUT web-site from Tuesday
15th July 2014:
www.sut.org
 Hardcopies available £15 per copy from SUT.
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For more information contact:
www.sut.org
Or
OSIG sub-committee Chairman
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