Cyclic loading of piled foundations has been the object of considerable research since the 1980s due to the use of piles for offshore oil and gas platforms and, more recently, offshore windfarms. Onshore piles are also presenting design challenges, as they are increasingly being used as an integral part of ground source heating and cooling systems, which results in cyclic thermal expansion and contraction.
Paul Bailie’s winning work was based on research carried out as part of his MSc at Imperial College, London. His work was also selected for presentation at the 2016 British Geotechnical Association’s Young Engineers Symposium.
How Oasys proved invaluable
Paul developed a numerical model to study pile behaviour under axial cyclic loading from both mechanical loading and thermal loading.
He showed how the t-z model had been implemented into Oasys Pile, illustrating his approach with comparisons between London Clay pile cyclic load test results and modelled pile behaviour. These comparisons determined how well the logarithmic t-z formulation represents real cyclic pile behaviour, and established the typical range of the parameters used in the model.
The Oasys Pile analysis presented in the competition submission made use of the recently implemented load-transfer (t-z) method on the settlement side of the program to study the performance of two test piles subjected to various axial cyclic loading conditions.
The soil parameters for the London Clay geology were based on available ground investigation data as well as typical values used for this material. Staged loading of the piles, including mechanical and thermal loading cycles, was input to match the cyclic loading and heating/cooling cycles applied to the test piles.
After comparing the pile head displacements from the Oasys Pile analysis to the displacements measured during pile load testing, we varied the curve fitting parameters for the logarithmic t-z curves (displacement to peak stress and the yield parameter) until a good match between modelled and real pile performance was found.