Influence of non-linear behaviour of soils on the performance of bored piles.

The complete load-settlement behaviour of piles can be assessed by using analytical and numerical methods or by performing load tests. The latter is to be preferred when one wants to take into account the actual soil-pile interaction. Alternative, useful and direct approaches rely on elastic formulae, normalised curves and load transfer curves. The main shortcoming of elastic approaches is the incapability of taking into account soil non linearity, that influences greatly the load-settlement behaviour, even at low load levels. In this paper an approach to obtain operational stiffness values to be used for forecasting pile settlement is presented. They are supplied in terms of stiffness decay curves, obtained by the analysis of many load tests performed on large diameter bored piles. By the estimation of the initial stiffness (before pile execution), and use of the proposed charts it is possible to evaluate the load corresponding to a well defined settlement, by means of some classic elastic relationships, that is a non linear load settlement curve.