This paper describes two different methodologies of transferring high tension loads through large diameter bored piles into the ground. The installation of post tensioned stress bars into the piles was considered as one option for the SOUL project however the use of high strength concrete (fc` ≥ 85 MPa) for the pile shaft had some essential advantages.
The use of high strength concrete for bored piles has hitherto been considered to be problematic. Workability criteria have to be maintained for several hours in order to achieve the required quality. Possible concrete shrinkage of the pile shaft causing cracks, concrete bleeding as well as an ongoing quality control of the concrete mix are only a few of the challenges that have to be considered.
This is particularly the case for the foundation piles of a high rise building where extremely high point loads are transferred through the piles into the ground. All piles have to be constructed to extremely high standards. In most cases geometry constraints and the design requirements of the superstructure make it impractical to install additional piles in the event that a pile does not achieve the required capacity and has to be supported or replaced by an adjacent pile.