ALPACA: Axial-Lateral Pile Analysis for Chalk Applying multi-scale field and laboratory testing

Lead Research Organisation: Imperial College London
Department Name: Civil & Environmental Engineering

Abstract

Chalk is a highly variable soft rock that covers much of Northern Europe and is widespread under the North and Baltic Seas. It poses significant problems for the designers of large foundations for port, bridge and offshore wind turbine structures that have to sustain severe environmental loading over their many decades in service. Particular difficulties are faced when employing large driven steel piles to secure the structures in place. While driven pile foundation solutions have many potential advantages, chalk is highly sensitive to pile driving and to service loading conditions, such as the repeated cyclic buffeting applied to bridge, harbour and offshore structures by storm winds and wave impacts. Current guidance regarding how to allow for difficult pile driving conditions or predict the piles' vertical and lateral response to loads is notoriously unreliable in chalk. There is also no current industrial guidance regarding the potentially positive effects of time (after driving) on pile behaviour or the generally negative impact of the cyclic loading that the structures and their piled foundations will inevitably experience. These shortfalls in knowledge are introducing great uncertainty into the assessment and design of a range of projects around the UK and Northern Europe. Particularly affected are a series of planned and existing major offshore wind farm developments. The uncertainty regarding foundation design and performance poses a threat to the economic and safe harnessing of vital renewable, low carbon, offshore energy supplies. Better design guidelines will reduce offshore wind energy costs and also help harbour and transport projects to progress and function effectively, so delivering additional benefits to both individual consumers and UK Industry.

The research proposed will generate new driven pile design guidance for chalk sites through a comprehensive programme of high quality field tests, involving multiple loading scenarios, on 21 specially instrumented driven tubular steel test piles, at an onshore test site in Kent. This will form a benchmark set of results that will be complemented by comprehensive advanced drilling, sampling, in-situ testing and laboratory experiments, supported by rigorous analysis and close analysis of other case history data. The key aim is to develop design procedures that overcome, for chalk, the current shortfalls in knowledge regarding pile driving, ageing, static and cyclic response under axial and lateral loading. The main deliverable will be new guidelines for practical design that will be suitable for both onshore and offshore applications.

Planned Impact

ALPACA brings together academics with leading expertise and proven track records in effective dissemination and industrial impact to tackle a key issue that affects the UK's and Europe's renewable energy, trade and transport sectors. The scientific innovation lies in conducting a novel programme of field and laboratory experiments, aided by rigorous analysis of the data, to develop a robust understanding of chalk behaviour and the key processes that affect piles driven in this notoriously difficult geomaterial. ALPACA will consider systematically previously unstudied factors including; driving 'friction fatigue', two-way axial cycling, scale effects, ageing, lateral loading and the latter's impact on axial resistance. The key audiences are developers and operators of wind farms, transport and port facilities, regulators, engineering consultancies and contractors driving piles in chalk, as well as academics researching Carbonate geomaterials.
The Industrial impact will be assured by the team's proven record of close engagement with practice which is reflected in the industrial monetary and in-kind contributions (totalling £518k). ALPACA will improve engineers' ability to understand and model Chalk's complex engineering response and so assist a wide range of infrastructure projects designed and constructed in Chalk. Slope stability, tunnelling and earthworks (which affect HS2 critically) will benefit as well as offshore and onshore foundations. ALPACA has the potential to deliver tens of £m in benefit to each major projects in which it is applied. Multiple dissemination routes will be followed to maximise impact:

1. We will form an ALPACA steering group that will meet twice per year and represent the relevant sectors. As shown in attached letters, members will include: from the wind energy sector, Mr Barbosa (SPR/Iberdrola), Mr Barwise (RWE/Innogy, the German energy utility), Dr Seidel (Siemens); from geotechnical consultancies, Mr Mackenzie (Fugro), Dr Puech (from the French SOLCYP cyclic pile JIP), Dr Taylor (Atkins) and Dr Schroeder (GCG); and from Independent Verification Bodies (IVB), Ms Hamre and Mr Maloney (DNV-GL). Other sponsors and steering group members may join once the project commences.
2. Independent academic expertise will be added by Dr Lawrence (ICL), Profs Lehane and Randolph (University of Western Australia, UWA), while Mr Muir-Wood (Wood Thilsted Partners Ltd.) will chair the committee. The industry and academic members will aid rapid dissemination of the key outputs.
3. Peer review and appearance in highly cited platforms adds great value to research and the Investigators' proven ability to publish enduring papers in high-quality open-access journals and high-profile conferences will provide another key route to impact.
4. Project-dedicated workshops will also be held that will engage the project partners. Later sessions will be opened, to maximize dissemination, to other researchers, including the SOLCYP and UWA teams, as well as project developers, geotechnical consultants and representatives from IVBs. A key output for practitioners will be a summary design booklet that will set out, step-by-step procedures for a wide variety of applications. The workshops and design booklet will complement the detailed research papers on which the new design approaches will be based.
5. Impact and dissemination will be further facilitated through the Investigators' strong professional links and membership of key committees in the British Geotechnical Association, the Society for Underwater Technology, the American Petroleum Institute, the International Standards Organisation and other bodies.
6. The Investigators' roles in EPSRC funded initiatives including the OU REMS and ICL Sustainable Civil Engineering CDTs will also offer opportunities to highlight the research and spread its adoption, as will their teaching in well-established Masters' and professional development courses run at ICL and OU.

Publications

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Buckley R (2020) Optimization of Impact Pile Driving Using Optical Fiber Bragg-Grating Measurements in Journal of Geotechnical and Geoenvironmental Engineering

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Jardine R (2019) Improving the design of piles driven in chalk through the ALPACA research project in Revue Française de Géotechnique

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Jardine R.J., Buckley, R.M; Kontoe, S.; Barbosa, P.; And Schroeder, F.C. (2018) Behaviour of piles driven in chalk.

 
Description Our field testing programme has been extended with new funding obtained from Industry and ORE Supergen, covernign several tests on very large instrumented piles, as well as some further laboratory testing. We will complete our final analysis of the last data in March 2022. Our work has showed how to improve the design of piles driven for windturines at chalk sites in a set of game changing papers. We have submitted four papers to the leading international journal Geotechnique on our laboratory and in-situ field testing on soils properties, with two other papers on the pile behaviour under monotonic and cyclic axial loading. Our final paper, covering lateral loading should be submitted in May 2022. Other papers are in preparation on our related work on the numerical analysis of the experiments through advanced FEM treatments.
Exploitation Route The project's Industrial Steering Committee were able to conclude from our work to date that (i) the Chalk ICP-18 rules for assessing driving resistance work very well, (ii) axial set up is affected by previously unappreciated physio-chemical processes which may dominate for driven piles having the scale of the ALPACA piles and operate at different rates above and below the water table, (iii) long term local axial shaft capacities exceed the recommendations given in current CIRIA design recommendations, (iv) brittleness of chalk has a dominant effect on the piles' lateral response to static loading, leading to far lower resistances than might be expected from peak laboratory shear strength measurements and (v) that cyclic axial and lateral loading can degrade shaft resistance.
The ALPACA fieldwork raised important questions regarding the effect of pile diameter and wall thickness ratio and we raised over £500k for an extended ALPACA Plus programme of field tests with additional ORE Supergen funding for the new tests which have now resolved all of the outstanding questions.
The Imperial College team also completed the parallel ALPHA programme led by PI Dr S. Kontoe and CoIs Profs L Zdravkovic and R Jardine, funded by ORE Supergen and started in November 2019 to conduct advanced numerical modelling of the ALPACA lateral pile tests.
These two extensions helped to deliver the new design methods that were targeted in the original ALPACA proposal. The work conducted in 2021 added to the important impact the work is having on industrial design rules for offshore windfarms sited in chalk ground profiles. The work is also relevant to harbour and bridge works onshore.
Sectors Construction,Energy,Environment,Transport

URL http://www.imperial.ac.uk/geotechnics/research/research-projects/alpaca/
 
Description The results emerging from the research haev been communicated to the project's ten industrial co-sponsors, who are making use of the findings in a range of projects. These include (i) the instrumentation of expensive offshore pile tests for a major offshore wind project offshore Taiwan and (ii) the French Le Treport offshore wind project and (iii) the German Baltic Parkwind project. The work has also led to keynote talks at specialist conferences held in 2018 in Vienna (August), London (September 2018), Paris (December 2018) and in Copenhagen (February 2019), Reykjavik (September 2019), Hanover (October 2019), Taipei (Taiwan, November 2019), GeoChina (September 2021), Brazil (September 2021) and teh upcoming McClelland Lecture (September 2023). The project is now well known internationally and is affecting engineering practice.
First Year Of Impact 2018
Sector Construction,Energy
Impact Types Economic,Policy & public services

 
Description High pressure laboratory triaxial testing on chalk 
Organisation University College London
Country United Kingdom 
Sector Academic/University 
PI Contribution We are undertaking new high pressure laboratory triaxial testing on chalk, which is revealing important new information about the chalks behaviour which has a very important impact on the lateral loading behaviour of piles driven in chalk, which dominates the foundation behaviour of monopile wind-turbines.
Collaborator Contribution Professor Coop's group at UCL are providing us with access to their new high pressure triaxial testing equipment. We are supplying high quality samples and post-doc testign staff and are liaising with UCL regularly regarding the test design and interpretation.
Impact Too early to say
Start Year 2019
 
Description Our ten industrial sponsors and partners 
Organisation Government of Sweden
Department Vattenfall
Country Sweden 
Sector Public 
PI Contribution They are co-funding the work and adding value through contributions in kind and through advising our steering committee
Collaborator Contribution To date these include drilling and sampling operations and technical advice as well as £350k in cash funding.
Impact The work is ongoing and technical leading to economic and societal benefits
Start Year 2017
 
Description Our ten industrial sponsors and partners 
Organisation Parkwind
Country Belgium 
Sector Private 
PI Contribution They are co-funding the work and adding value through contributions in kind and through advising our steering committee
Collaborator Contribution To date these include drilling and sampling operations and technical advice as well as £350k in cash funding.
Impact The work is ongoing and technical leading to economic and societal benefits
Start Year 2017