Screw piles for wind energy foundation systems

Lead Research Organisation: University of Dundee
Department Name: Civil Engineering

Abstract

Screw (or helical) piles are foundations which are screwed into the ground. They are widely used onshore for supporting motorway signs and gantries as they possess good tensile and compressive resistance. This project aims to make screw piles a more attractive foundation (or anchoring) option offshore for wind farms, which are being deployed in deeper water and subject to increasing performance demands. The UK has challenging targets for expansion of energy from renewables with the potential for over 5000 offshore wind turbines by 2020. The necessary move to deeper water will increase cost and put greater demands on subsea structures and foundations. The current foundation solutions being considered for these applications are driven piles, large monopiles or concrete gravity based structures (GBS). Driving of piles in large numbers offshore causes concerns over plant availability and impact on marine mammals. There are also concerns over the limit of practical monopile development and the high material demands of GBS. Screw piles have the potential to overcome these issues and are scalable for future development from current onshore systems which have relatively low noise installation and are efficient in terms of both tensile and compressive capacity. To meet offshore demands, screw piles will require geometry enhancement but it is envisaged that these will initially be modest to allow de-risked transfer of onshore technology offshore. This will lead to the deployment of several smaller piles or pile groups rather than moving straight to very large single screw piles that may prove difficult to install and require significant investment.
To allow screw piles to be considered as a foundation solution for offshore wind this project will develop piles with optimised geometries that minimise resistance to installation but are capable of carrying high lateral and moment loads. In order to install screw piles torque devices are used to effectively screw the anchors into the ground. With increased pile size requirements and potential changes in geometry this project will develop improved, less empirical techniques to predict the torque required in a variety of soil conditions. This will allow confidence in pile installation and investment in appropriately sized installation plant. As new pile geometries are being developed these will need to be tested (through model, numerical and field testing in this project) to verify that they can meet the performance demands of the offshore environment. The project will also develop bespoke analysis techniques to allow consulting geotechnical engineers the tools they require to design the foundations and contractors the tools to inform the installation processes. As piles can be deployed as large single units or smaller units in groups the efficiency of group deployment and multiple foundation geometries will be explored, as using several smaller geometry foundations could reduce the risks during offshore installation and actually be more economic due to lower fabrication costs and demands on installation plant. The areas of investigation above will be combined to produce a design and decision making toolkit for use by geotechnical designers to allow deployment of screw piles as offshore foundations in an efficient and cost effective manner.
The research has the potential to make it easier to deploy screw pile foundations for offshore renewables. This project will develop foundations able to deal with current water depths and will provide understanding of the behaviour of piles as water depths and the demands on the foundations increase. By harnessing the installation and performance benefits of screw pile/anchor technology, the results of the project will contribute to an overall cost reduction in electricity generated by renewable means and increase the public's confidence in the future viability of this energy source.

Planned Impact

Beyond academia this research project will lead to economic and environmental impacts:
a) This project will accelerate the development of an alternative foundation system for offshore wind which is expected to carry a reduced overall foundation system cost, compared to currently proposed solutions which in some cases exceed the manufacturing capabilities of the UK. As renewable energy projects require many more individual installations than oil and gas applications, small efficiencies can result in huge overall project savings and allow sites to be developed that may currently be considered uneconomic. These reductions in the cost of foundation fabrication and installation will be passed onto the developer, operator and ultimately to the UK consumer via a reduction in the cost per GW of offshore wind energy generated. This will also therefore assist in improving the public perception of the viability of offshore wind farms.
b) The proposed foundation design tools that will be developed will aid Geotechnical engineers to select the most appropriate foundation solution and deployment strategy to suit the water depth and geotechnical conditions. This will give enhanced confidence in deploying adventurous foundation types in new environments for offshore wind. This will result in a competitive edge for UK foundation contractors that will allow them to export their expertise internationally.
c) Offshore wind farm developers will be able to choose from a greater range of foundation solutions coupled with subsea structure alternatives (monopod or jacket structures) that give the greatest economic and performance benefits. Installation contractors will be able to plan, design, build and invest in infrastructure that is appropriately scaled to actual deployment requirements. This reduction in uncertainty will make it easier to attract financial investment in adventurous and novel techniques. In turn this will give UK machine and equipment developers economic advantage over competing overseas technology.
d) The research will contribute to new analysis techniques that will be implementable in commercially available pile design software (e.g. OPile) and as a module within mooring analysis (e.g.Orcaflex). This will assist with take up of screw piles as a beneficial alternative foundation technology both onshore and offshore. Development of 3D large deformation modelling that can simulate complex installation processes (such as screwing a pile into soil and determining the effect on the soil state) and which can then be implemented in a standard FE code has a wide potential for take up in the modelling of other complex geotechnical installation processes and similar processes in other engineering disciplines.
f) The proposed technique will be a comparatively 'silent' approach compared to driven piles. The greatly reduced noise and vibration will be less disturbing to marine mammals. It will therefore also have an associated additional economic benefit in removing the need for expensive noise-mitigation techniques.
g) The installation process can be applied in reverse to 'unscrew' the piles from the ground at the end of the project's life. This ability to completely decommission has benefits over classic pile types that are either left insitu of cut off below the seabed, thus the site can more easily be returned to its original state. The ability to remove the piles would potentially also allow re-use in future applications.
The project will develop the skills of the three post-doctoral research associates (PDRAs) in geotechnical modelling, computational geotechnics and advanced field and laboratory testing. The PDRAs will also develop specialist geotechnical knowledge relevant to the offshore renewables sector making them a valuable future asset in either academia or to renewables consultancy/contracting.

Publications

10 25 50
 
Description EPSRC Supergen Offshore Renewable Energy (ORE) project, Research Alignment Group (RAG): Invited member
Geographic Reach Multiple continents/international 
Policy Influence Type Participation in a advisory committee
Impact EPSRC Supergen Offshore Renewable Energy (ORE) project, Research Alignment Group (RAG). Influencing future research direction of EPSRC offshore renewable energy research.
 
Description EU H2020 Marie SkLodowska-Curie Actions Individual Fellowships SAFS
Amount £173,000 (GBP)
Funding ID 753156 
Organisation Marie Sklodowska-Curie Actions 
Sector Academic/University
Country Global
Start 08/2017 
End 07/2019
 
Description Industrial funding by Roger Bullivant Limited
Amount £20,000 (GBP)
Organisation Roger Bullivant Limited 
Start 12/2017 
End 06/2021
 
Description National Productivity Investment Fund: EPSRC additional funding for doctoral studentships
Amount £65,000 (GBP)
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Academic/University
Country United Kingdom
Start 10/2017 
End 04/2021
 
Title Development of an inflight centrifuge screw pile installation and loading system 
Description To simulate the prototype installation behaviour of screw piles at realistic confining stress lev-els, a new installation and loading rig, consisting of two independently-controlled servo-motor drive systems was developed to allow screw pile models to be installed and axially load-tested inflight in one operation at 50 g. This system was developed around the Scalable Actuator Control System architecture (SACS) recently installed on the Dundee centrifuge, based around a National Instruments compactRIO controller with modu-larly scale-able servo drive interfaces. 1:50 scale model screw piles were manufactured from mild steel with 10 mm diameter cores with 25 mm diameter flanges welded on, representing a new generation of larger screw pile proposed for offshore marine renewable applications. These were installed up to 200 mm depth in dry dense sand to demonstrate the performance and capabilities of the new actuator. 
Type Of Material Improvements to research infrastructure 
Year Produced 2016 
Provided To Others? Yes  
Impact 236 views of the paper on Researchgate 
URL https://www.researchgate.net/publication/303737874_Development_of_an_inflight_centrifuge_screw_pile_...
 
Description Field testing of Screw piles 
Organisation University of Western Australia
Country Australia 
Sector Academic/University 
PI Contribution Use of characterised sand testing site
Collaborator Contribution Supporting instrumentation development and access to a test site
Impact Test data to support previous work in screwpile capacity estimation/modelling (tension and compression) using installation torque and crowd force
Start Year 2019
 
Description British Drilling Association (BDA) Technical session:solutions for the Future of Geotechnical Engineering: New CPT correlations for novel offshore renewable energy installations 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Industry/Business
Results and Impact British Drilling Association (BDA) Technical session:solutions for the Future of Geotechnical Engineering: New CPT correlations for novel offshore renewable energy installations. Part of the British Drilling Associations regional travelling programme to update the industry on the latest developments and innovations. Presentation to 50 people consisting of geotechnical consultants and contractors. Sparked questions and discussions afterwards.
Year(s) Of Engagement Activity 2018
 
Description ICE Northern Geotechnical Group: Annual seminar, Piling 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Industry/Business
Results and Impact 50 Industrialists attended a focused semianr session on piling given by industrial and academic speakers. Presentaion given on the use of screw piles as an alternative foundation type for offshore wind. Resulted in discussion and question and answer and follow email enquiries.
Year(s) Of Engagement Activity 2017
 
Description IET's First Lego Dundee University leg 
Form Of Engagement Activity Participation in an open day or visit at my research institution
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Schools
Results and Impact University of Dundee hosted a regional heat of the IET Lego Mindstorms international competition. The competition aims to encourage school pupils into science and engineering, by completing a range of competition tasks using programmable Lego robots built by the pupils.
As a part of this event, a Civil Engineering stall was setup to provide activities for the pupils when they were not competing and over lunchtime. The aim of the stall was to:
• Provide pupils with an understanding of what civil engineering is
• Raise pupils interest in Civil Engineering in a fun and engaging way
• Highlight the importance of Civil Engineering in fields such as renewable energy, infrastructure and earthquake resilience
The display included Lego models of offshore wind turbines and seabed cable ploughs, posters of Civil Engineering topics and leaflets with further information on how to pursue engineering as a career path for those pupils interested.
Practical activities were available for the students focussed on EPSRC funded projects at the University of Dundee:
• Screw piles: Pupils were able to test Lego models of both straight shafted and screw piles embedded in sand and compare the differences in pullout force
• Seabed ploughing: Pupils were able to watch interactive videos of the seabed ploughing process and interact with model Lego cable ploughs
• Earthquake liquefaction: Students were able to design and make their own foundations for a Lego model house and compare how it coped with earthquakes using a miniature shaking table.
100 school pupils visited the stall during the day, with the majority of pupils undertaking all of the activities listed above.
Year(s) Of Engagement Activity 2016
URL https://www.dundee.ac.uk/scienceengineering/news/2016/article/first-lego-league-takes-place-at-unive...
 
Description Kyushu Univeristy, Japan, Invited speaker: Centrifuge modelling of screw piles for offshore wind energy foundations 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Postgraduate students
Results and Impact Kyushu Univeristy, Japan, Invited speaker: Centrifuge modelling of screw piles for offshore wind energy foundations. Presentation to 20 post graduate students and research staff. Led to discussion on joint research projects in the future.
Year(s) Of Engagement Activity 2018
 
Description Screw pile foundation performance seminar 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Workshop/seminar on screwpile design and performance by Dr Anthony Blake at University of Western Australia, Centre for Offshore Foundation Systems (COFS).

The audience comprised international visitors to COFS and local offshore geotechnical design specialists and p/g/r and u/g students.
Year(s) Of Engagement Activity 2019
 
Description University of Sheffield Colloqium series on Mechanics and Infrastructure research 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Postgraduate students
Results and Impact 60 post graduate ad undergraduate students attended an invited presentation at the University of Sheffield Engineering School on Physical Modelling for Offshore Energy Infrastructure Deployment which sparked questions and discussion afterwards and raised awareness of the use of physcial modelling and interesting research areas for renewable energy research.
Year(s) Of Engagement Activity 2016