Group interactions in large-diameter bored pile groups subjected to torsion (PI: Prof. Zhang LM; PhD student: Mr. Kong Linggang, Dr Chen Shengli)

Large structures such as deep-water offshore platforms, tall buildings, and tall bridge bents are usually supported by pile foundations and are subjected to horizontal loads of considerable magnitude due to wind and wave action.  These horizontal loads can transfer significant torsional forces to the piles by virtue of eccentric lateral loading.  This is especially the case in Hong Kong, where typhoons are very strong and the wind pressure on high-rise structures is very high.  However, little has been known about the torsional response of large-diameter pile groups and the limit states against torsion are often not well addressed in practical design.  Catastrophic failures of bridge piers and tall buildings have been reported due to the action of coupled lateral and torsional loads. 

The principal objective of this research project is to investigate the group interactions in large-diameter bored pile groups subjected to torsion.  A state-of-the-art 400 g-ton geotechnical centrifuge will be used to simulate the torsional response of the large diameter pile groups of several geometries in both dense and loose foundation soils.  In a centrifuge model, the stress conditions are the same as those existing in a full-scale construction.  Therefore, the centrifuge model can reproduce the prototype behaviour better than conventional models conducted in 1-g gravity condition.  A four-axis robotic manipulator will be employed in the centrifuge as an automated, convenient platform for applying torsional loads to the model pile groups and for characterising soil behaviour in flight.  Laboratory testing of the foundation soils and numerical analyses of the pile groups subjected to torsion will also be conducted.  Findings from this project will provide valuable information and insight into the torsional response of pile groups, and a rigorous basis for optimum design of pile foundations subjected to all three basic loadings (axial, lateral, and torsional).  This may in turn lead to the establishment of design guidelines including torsion.