Long-term behaviour of offshore pile foundations under cyclic loading
This joint PhD project is based at the Shanghai Jiao Tong University with a 12 month stay at The University of Melbourne.
Oﬀshore wind power becomes one of today’s fastest growing renewable energy sources and the frontier of marine developments in China. Currently, the capacity of oﬀshore wind turbines has reached 6.8 GW, and 75% of the available wind turbines use pile foundations. As most pile foundation located in soft clay seabeds in China, one critical issue of the foundation is the accumulated deformation under long-term cyclic loads. This project will conduct systematic experimental and numerical studies to investigate the pile behaviour under long-term cyclic loading, where a new design framework will be proposed through the close collaboration between SJTU and UoM.
This project aims to advance the understanding of pile-soil interaction and propose a new design approach for pile foundation. The scopes of work in this project include:
- to investigate the pile-soil interaction in clay through advanced numerical ﬁnite element modelling and rigorous geotechnical centrifuge modelling. The eﬀect of soil compaction and coupled soil-pore water will be examined in the soil domain around piles;
- to explore the inﬂuence of the number of cycles on soil weakening through laboratory testing, which will be used to calibrate our advanced soil constitutive model (based on the bounding surface framework). The ratcheting eﬀect of stress-strain relationship of clayey soils will be investigated by relating to the stress-induced anisotropy. From the cyclic triaxial tests, soil over consolidation and structure will be scrutinised to calibrate and advance existing advanced soil model;
- to propose a new design tool that can be readily employed by oﬀshore engineers to calculate the long-term deformation of pile foundations.
The research works, including laboratory cyclic triaxial tests, development of constitutive model, extensive numerical simulations and centrifugal model tests, will be conducted by the collaborative teams. Special attention will be focused on the pile-soil interaction in marine clay and stress-strain response of soil around pile under long- term cyclic loading. These scientiﬁc problems will be solved through a close collaboration between SJTU and UoM. Two teams’ activities mainly include the following four aspects:
- SJTU: A large number of cyclic triaxial tests will be carried out to study the strain accumulation and stiﬀness attenuation characteristics of marine clay under long-term cyclic loading;
- SJTU: Based on the cyclic triaxial test results, our elastoplastic constitutive model will be improved to allow an accurate description of the strain accumulation subject to a large number of cyclic loading;
- UoM: Based on the improved constitutive model, the law of soil weakening and plastic deformation around the pile under long-term cyclic load will be explored and further implemented into ﬁnite element package;
- SJTU: Batches of centrifuge tests will be carried out to observe the cumulative plastic deformation of the soil around the pile and the pile-soil interaction during the loading process.
The team members at SJTU and UoM have extensive expertise in oﬀshore geotechnical engineering and have been well known with world-class testing facilities and numerical modelling capability.
Out of the 4 research activities listed above, the laboratory testing, constitutive model development and geotechnical centrifuge modelling will be conducted at SJTU. The numerical analysis will be carried out by the SJTU PhD student co-supervised by CI Tian and the team during the one year visiting to implement the advanced elatoplastic soil model into ﬁnite element package ABAQUS.
The research outcomes from this project will fundamentally beneﬁt the oﬀshore industry by providing more reliable knowledge-based design method for pile foundation to underpin oﬀshore wind development, to enable the competence of oﬀshore renewable sector over traditional energies.
The project will be complemented by the project Developing a novel foundation to secure floating renewable energy turbines and the collaboration will ensure a successful completion of the project.