SuperPile 2017 Online Proceedings, (DFI)
Installation and performance of Continuous Helical Displacement (CHD) piles in London Clay
Jonathan Ball, BSc (Hons) CGeol EurGeol FGS
Continuous Helical Displacement (CHD) piles are an alternative to bored piles that Roger Bullivant Ltd have been developing over the last 20 years, and have become a popular product within our portfolio. The installation of the pile does not bring any spoil to the surface, so this makes it a very popular choice for construction on brownfield sites where contamination is an issue. The pile itself consists of screw-shaped pile shaft, with an inner core of 300mm or 400mm, and an outer flight diameter of 600mm or 700mm. Piles are suitably reinforced within the inner column to deal with any shear or lateral forces acting upon the member, and a central bar is often introduced to account for any clay heave due to desiccation, and for surface heave generated during installation. Our current design methodology for CHD piles in clay is based upon increased alpha values from a more traditional soil/concrete pile interface to reflect the fact that the pile is designed to fail as a cylinder incorporating the soil between the flights, and therefore more akin to a soil/soil interface. As a result, the system can result in a significant reduction in overall foundation costs by reducing pile lengths and material usage. The aim of our presentation is to look back at the installation of a number of CHD piles in London Clay at Kidbrooke Village, a large scheme across numerous phases where we have undertaken a significant number of working and preliminary pile tests, and present our findings to the group. We will also highlight future developments we are proposing for the system, such as our Continuous Helical Augured Displacement (CHAD) pile, and upcoming work regarding torque data and pile capacity, and the prediction of installation heave.
|article #2673; publication #1031 (SP-2017)|