The design of piles is typically undertaken using empirical or semi-empirical methods developed for ‘regular’ silica sands or clays. The application of such methods to geological materials whose physical characteristics are unlike those on which the conventional design methods were derived can result in unconservative estimates of pile capacity. The pumiceous deposits that occur extensively throughout the central North Island of New Zealand are one group of materials where such standard methods of design must be used with caution. Pile tests undertaken as part of the Stella Passage Bridge and Tauranga Harbour Bridge projects have provided a rare opportunity to examine the performance of different pile types within pumiceous soils. Although the highly frictional nature of pumiceous soils can lead counter-intuitively to lower shaft capacities, the use of grouted or bored piles can give very good performance through the establishment of good soil-pile wall contact.
NZGS Symposium