Pile-soil Interaction And Assessment Of Design Methods Of Capacity Of Axial Loaded Driven Piles In Clay

As one of the important foundations, piled foundation is used extensively to underpin major bridges, wind turbines, port and offshore structures, and so on. These piles are normally driven piles with large diameter and long lengths. However, due to the limitation of expenses, equipment, construction period and field conditions, static load tests of piles are difficult to conduct or failure loads are not easy to apply in the tests, and their ultimate bearing capacity cannot be determined accurately. How to calculate the axial capacity of piles is therefore of vital importance in geotechnical engineering. Predictions based conventional empirical design methods is far beyond the expectations of practical engineers. Up to date, there is no reliable design method that has received wide acceptance to calculate the ultimate bearing capacity for driven piles.This dissertation presents a study on the pile-soil interaction and assessment of design methods of axial capacity of piles driven in clay. Mainstream approaches to calculate the pile capacity include finite element method (FEM), cavity expansion method (CEM) and strain path method (SPM), among which FEM is more often used to consider the pile-soil interaction during the pile installation and pile under loading conditions. In order to gain a profound understanding of the mechanism of pile-soil interaction and overcome shortcoming of empirical approaches, instrumented driven pile tests in the field can offer stress distributions during the pile driven process and following loading tests.Based on pile loading tests and database analyses, several research groups have proposed different calculation methods. However, the varying quality of tests in databases may lead to very different performance of these methods when they are applied to new test cases. There is need to establish a more representative database of load tests with more stringent quality control criterions for the assessment of design methods. To this end, a Zhejiang University (ZJU)-Imperial College London (ICL) database is established and composed of 70 high-quality load tests of driven piles in clay from literature review, own projects and research communications. The performance of each method is evaluated by the statistical mean value and coefficient of variability. Based on the database assessment, time effects on pile capacity is also concerned.Noting that FEM has been widely used in engineering problems, a commercial software ABAQUS integrated with Coupled Eulerian Lagrangian (CEL) technique, which is able to overcome the mesh distortions due to large deformation during pile installation is employed. CEL based numerical analysis gives the stress distributions during the pile installation, which is reasonably well with the field measurements. This method offers an avenue to investigate the pile-soil interaction.