ALPACA: Axial-Lateral Pile Analysis for Chalk Applying multi-scale field and laboratory testing
Oxford University: Byron Byrne and Ross McAdam
Funded by: EPSRC and Industrial sponsors: Atkins, DNVGL, Fugro, GCG, Iberdrola, Innogy, LEMS, Siemens
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 must 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 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.