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 (frothe 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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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 main testing programme is still underway, but we have achieved important early results regarding (i) the successful use of Fibre Bragg Grating gauges in pile driving monitoring and have a publication submitted on this topic, (ii) the effects of steel chemistry and groundwater conditions on the behaviour of piles driven in chalk, (iii) how cyclic loading degrades axial capacity and lateral stiffness for piles driven in chalk. We also have very promising results regarding the mechanical characterisation of intact and remoulded chalk materials.
Exploitation Route We are still in the middle of our project, but the work will have an important impact on industrial design rules for offshore windfarms sited in chalk ground profiles.
Sectors Construction,Energy

URL http://www.imperial.ac.uk/geotechnics/research/research-projects/alpaca/
 
Description Although the project is still underway the results emerging from the research are being communicated to the projects ten industrial co-sponsors, who are making use of the initial 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), Paris (December) and in Copenhagen (February 2019) with a further talk planned for Reykjavik in September 2019. The project is now becoming well known internationally.
First Year Of Impact 2018
Sector Construction,Energy
Impact Types Economic,Policy & public services