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Quietly does it…

When foundation piles are being hammered into the ground in readiness for construction, everyone knows about it. Recent legislation has limited the amount of noise and vibration that can be tolerated in urban areas, however, forcing contractors to seek alternative methods for inserting piles.

The most common design solution has been to bore holes and cast piles in place. This method has the twin disadvantages that the spoil from the boreholes is increasingly hard to dispose of plus the piles are not easy to remove following demolition. In addition, the complex installation process for these piles prevents the accurate prediction of pile capacity; current design methods are unreliable.

A novel pile installation technique known as the 'Press-in Method' and developed in Japan by Giken Seisakusho Ltd overcomes these problems. A robotic machine is used to jack each foundation pile into the ground by static force alone. Professor Malcolm Bolton explains: "With a new technique such as this, contractors are understandably wary about the strength and reliability of the resulting piles. We were originally approached by Giken Seisakusho to look at their method in 1995 and we have had two or three undergraduate students working on the project every year since then. The students have the wonderful experience of going out to Japan and working on site with Giken engineers each summer. The students analyse the data they have collected during the course of their fourth year project."

David White, now a Research Fellow, was one of those students. He has just completed a PhD looking at the soil mechanics involved in press-in piling, and is now encouraging civil engineers in the West to consider this environmentally-friendly construction technique.

"It transpires that by pressing-in foundation piles, we can predict the long-term capacity with much greater certainty. The installation process involves applying a known load to the pile in the same manner as during the working life of the foundation. Furthermore, by taking advantage of the control offered by these robotic machines, we can optimise the geometry of the foundation. Recent field tests proved an efficient new design in which the resistance offered by each pile when loaded as part of a foundation is greater than the resistance offered during installation; the extra capacity is 'switched on' by the novel geometry. In addition, we have detected an increase in the capacity of each pile with time.

With conventional piling systems, engineers reduce the estimated foundation strength by a large safety factor to combat the uncertainty within pile design. With pressed-in piling, we can be more confident about the foundation performance, improving the design efficiency."

So the new method wins out both on grounds of reduced noise and vibrations, as well as a reduction in the amount of material that has to be used. The group are now investigating the possibility of using the method for the construction of bridge foundations, and the first tall building founded on pressed-in piles is currently under construction in Tokyo. With these exciting developments under way, the cultural exchange looks likely to continue for some years.

For further information, please contact Professor Malcolm Bolton: T: 01223 742367 email: mdb@eng.cam.ac.uk