SOURCE: Improved insitu Stiffness measurements for Offshore foundation design considering Uncertainty, Repeatability and Common sources of Error

Lead Research Organisation: University of Glasgow
Department Name: College of Science and Engineering

Abstract

The UK is the world leader in offshore wind energy; almost 40% of global capacity is installed in UK waters. A new ambitious target of 40GW of wind power by 2030 aims to produce sufficient offshore wind capacity to power every home, helping to achieve net zero carbon emissions by 2050. Offshore wind turbine (OWT) foundations, which are typically steel monopiles, contribute approximately 25% to a windfarm's capital cost. The size of OWTs is increasing rapidly and continued optimisation of foundation design is paramount. Recent research has led to significant advances through theoretical developments combined with high-quality field-testing. Despite recent advances, there remains significant uncertainty in the measurement and interpretation of key soil deformation parameters that underpin new and existing design approaches.

The central aim of SOURCE is to use rigorous measurement and interpretation in the field and laboratory to quantify and reduce material parameter uncertainty and minimise the impact on the predictive capability of OWT foundation design methods. Improved site characterisation will contribute to increased security in design, lowering capital costs, subsidies and carbon emissions and meeting the UK's ambitious new energy targets.
 
Description The aim of the project is to improve the security and reliability of in situ stiffness measurements for use in offshore foundation design methods. The work has involved multi-method geophysical testing and laboratory testing at three sites. The analysis of the first chalk dominated site is complete and has led to important insights. The study has highlighted the importance of a targeted approach to test execution and data acquisition in such (relatively) high velocity materials. Each of the in situ testing methods investigated has relative merits and where comparable measurements could be made there appears to be small differences between the values of in situ shear stiffness obtained.
Characterisation of thin layer features, such as flint bands and dissolution features is more robust when smaller receiver spacing and/or lower depth increments are adopted. The choice of in situ testing technique should be targeted to the particular application e.g. cross-hole or pressuremeter testing would be ideally suited to characterisation of profiles for laterally loaded piles while tunnelling applications may require the use of PSL or or DH testing with small receiver spacing where small local variations in stiffness can be resolved effectively. In the offshore environment, where downhole and crosshole geophysics are difficult to execute, PSL combined with SCPT in shallow layers may give representative profiles, particularly where noise interference may affect near-surface PSL readings. The chalk's mass stiffness is controlled by the network of fractures present in the chalk mass, leading to poor correlation with laboratory element tests and highlighting the requirement to take in situ measurements for use in geotechnical analyses. Importantly, where only laboratory stiffnesses are available for use in design, designers should make careful judgements to reduce the values to account for the in situ chalk's micro to macro fissuring pattern.
Exploitation Route See above
Sectors Construction

Energy
 
Description Application of Distributed Acoustic Sensing at SOURCE sites 
Organisation University of Leeds
Country United Kingdom 
Sector Academic/University 
PI Contribution During a steering committee meeting an idea was formed to trial Distributed Acoustic Sensing at the SOURCE sites. Distributed acoustic sensing can give more continuous and stable measurements than traditional sensors, however its use in geotechnics is not well documented. The research team and PI assessed the feasibility and constructability of the technology before contacting additional partners.
Collaborator Contribution A collaboration is underway with the University of Leeds' Institute for Applied Geoscience who have expertise in DAS technology. The technology will be deployed at the final SOURCE testing site in Summer 2023. For this work we have leveraged additional IAA funding to support a PhD student contributing to the fieldwork.
Impact TBC. Multi-disciplinary - geotechnics and earth science
Start Year 2023
 
Description Steering committee meetings 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Industry/Business
Results and Impact Kick of meeting to commence the project in Nov 2022. Regular steering committee meetings thereafter. These have been essential in developing the research ideas, keeping the research on track and communicating early outcomes.
Year(s) Of Engagement Activity 2023,2024