Offshore Wind Accelerator Suction Installed Caisson Foundations for Offshore Wind: Design Guidelines February 2019 TABLE OF CONTENTS TABLE OF CONTENTS ................................................................................................................................. i LIST OF TABLES ......................................................................................................................................... v LIST OF FIGURES ...................................................................................................................................... vi LIST OF APPENDICES ............................................................................................................................... vii Disclaimer .............................................................................................................................................. viii Acknowledgements ................................................................................................................................. ix 1. Introduction ............................................................................................................................ 1 1.1 Objectives .................................................................................................................... 1 1.2 Offshore Wind Accelerator background ..................................................................... 1 1.3 Suction Installed Caisson Foundations (SICF) background .......................................... 1 1.4 Stakeholders ................................................................................................................ 2 1.5 Extents and limitations ................................................................................................ 2 1.6 Document structure .................................................................................................... 3 2. Terminology, Notations and Abbreviations ............................................................................ 4 2.1 Terminology................................................................................................................. 4 2.2 Conventions ................................................................................................................. 7 2.3 Abbreviations .............................................................................................................. 7 3. Design Principles ...................................................................................................................10 3.1 Safety philosophy ......................................................................................................10 3.2 Limit states ................................................................................................................10 3.2.1 Ultimate Limit State (ULS) ...................................................................................10 3.2.2 Accidental Limit State (ALS) .................................................................................11 3.2.3 Fatigue Limit State (FLS) ......................................................................................11 3.2.4 Serviceability Limit State (SLS) .............................................................................11 3.3 Design Optimisation ..................................................................................................12 3.4 Design by LRFD (partial safety factor) method .........................................................13 3.4.1 Approach .............................................................................................................13 3.4.2 Load and material factors for WTG foundations .................................................14 3.4.3 Load and material factors for offshore substation foundations .........................15 4. Site Geotechnical Conditions ................................................................................................16 4.1 Site characterisation requirements ...........................................................................16 February 2019 – Issue 1.0 | i 4.2 Geotechnical hazards ................................................................................................17 4.3 Geophysical survey ....................................................................................................18 4.4 Geotechnical survey ..................................................................................................19 4.5 Ground model ...........................................................................................................21 4.6 Geotechnical parameters for design and installation ...............................................21 4.7 Special considerations for selection of soil parameters............................................22 4.8 Clustering...................................................................................................................23 5. Foundation Loading ..............................................................................................................24 5.1 General ......................................................................................................................24 5.2 Interfaces between model elements ........................................................................24 5.2.1 Sign convention ...................................................................................................24 5.2.2 Load reference point (interface point) ................................................................25 5.3 Foundation load components ...................................................................................25 5.4 Load cases .................................................................................................................25 5.5 Load generation and modelling.................................................................................26 5.5.1 Design process .....................................................................................................26 5.5.2 Integrated Load Analysis (ILA) / Coupled approach ............................................27 5.5.3 Sequential Load Analysis (SLA) / Uncoupled approach .......................................27 5.5.4 Comparison of Integrated and Sequential Load Analysis ....................................28 5.6 Foundation damping .................................................................................................29 5.7 Extraction of loads acting on SICFs ............................................................................30 5.7.1 Relevant load characteristics ...............................................................................30 5.7.2 Reporting .............................................................................................................31 6. Installation Design ................................................................................................................32 6.1 Installation design and risk management .................................................................32 6.2 Penetration resistance ..............................................................................................32 6.2.1 Mechanism-based methods ................................................................................34 6.2.2 CPT-based methods .............................................................................................36 6.3 Touch down and self-weight penetration .................................................................37 6.4 Suction installation ....................................................................................................38 6.4.1 Limits to suction pressures ..................................................................................38 6.4.2 Installation tolerances – penetration and verticality ..........................................41 6.5 Trial installations .......................................................................................................42 6.6 Non-homogenous soils for installation .....................................................................42 February 2019 – Issue 1.0 | ii 6.6.1 Installation in layered or heterogeneous soils ....................................................43 6.6.2 Installation in other materials .............................................................................43 6.7 Multi-chamber designs ..............................................................................................44 7. Site Installation Operations ..................................................................................................45 7.1 Criticality ....................................................................................................................45 7.2 Instrumentation ........................................................................................................45 7.3 Seabed preparation and scour protection ................................................................46 7.4 Lowering through splash zone (venting) and touchdown .........................................47 7.5 Self-weight penetration ............................................................................................48 7.6 Suction-assisted penetration.....................................................................................48 7.7 Underbase filling .......................................................................................................49 7.7.1 Considerations