CHD pile performance, part II:Numerical modelling

In this paper, a set of simple modelling procedures are presented that can be used to estimate the load-settlement behaviour of Continuous Helical Displacement (CHD) piles in sands, in conjunction with the Finite Element Method (FEM). The approach makes use of a stress and strain dependent non-linear soil model that can be parameterised using basic soil data (principally relative density) that can be determined through routine site investigation (e.g. SPT, CPT). The procedures are validated against a database of 1-g physical model tests reported in the Companion Paper, where they are shown to be suitable for estimating the load-settlement behaviour of CHD piles within the serviceability range. In this way they are complimentary to the analytical method for estimating the ultimate capacity of a CHD pile which was developed in the Companion Paper. In the final part of the paper, the FEM and analytical model are applied to four historical field pile load tests on CHD piles conducted at three different sand sites where they are (i) further validated; and (ii) used to discuss potential savings in pile material and therefore cost due to additional confidence in performance determination at both ultimate and serviceability limiting states

CHD pile performance, Part I:Physical modelling

The Continuous Helical Displacement (CHD) pile is an auger displacement pile developed by Roger Bullivant Ltd in the UK. It has performance characteristics of both displacement and non-displacement piles due to the nature in which it is installed. Based on field experience, it has been shown that the load-settlement performance of the CHD installed in sand exceeds the current design predictions based upon conservative effective pile diameter and design parameters associated with auger bored or continuous flight auger (CFA) cast in-situ piles. In an effort to gain a greater understanding of the performance of the CHD pile compared with more conventional piling techniques, a programme of model pile testing and associated Finite Element Modelling (the subject of a Companion Paper) in sand was undertaken. The model testing programme established that greater shaft resistance may be developed for CHD piles than had originally been considered. Based upon the results of the model testing, recommendations for more appropriate approaches to the selection of end bearing and shaft resistance factors are made to predict ultimate load capacity in sand