Page 302 - Numerical Analysis and Modelling in Geomechanics

Chapter 10
Analysis and design of pile groups

F.Basile

Introduction
In his 2000 Rankine Lecture, Professor Atkinson has emphasised the importance
of considering soil non-linearity in routine design. For pile group problems, this
issue has not yet been satisfactorily addressed, and current design practice is still
generally based on linear approaches. The main drawback to the application of
linear models to pile group problems is that they ignore the non-linear load-
deformation characteristics of soil and hence misrepresent the forces in piles,
specifically by giving higher stresses in group corners. The cost of this in
practice is high and there is an urgent need in industry for efficient non-linear
analysis methods.
An attempt at removing these limitations is represented by the load-transfer
approach which is the most widely adopted technique for the non-linear analysis
of single piles. However, this approach suffers from some significant restrictions
when extended to pile group problems.
A more practical non-linear approach for the analysis of pile groups under
general loading conditions (i.e. vertical loads, horizontal loads and moments) has
recently been proposed by Basile (1999) and some further developments and
applications of the method are described in this chapter. A review of available
computer programs for pile group analysis is presented, including some
applications in both the linear and non-linear range. The critical question of
estimation of geotechnical parameters is addressed, and attention is focused on
correlations between these parameters and commonly available in situ test data.
Finally, attention is turned to the application of available numerical methods to
practical problems involving real soils. A number of published case histories are
considered, and the predictions from selected methods of analysis are compared
with the field measurements.

Numerical methods for pile group analysis
Estimation of the deformations and load distributions in a group of piles
subjected to general loading conditions normally requires the use of computer-