Volume 6 – Geotechnical Manual, Site Investigation and Engineering ...

Chapter 9 FOUNDATION ENGINEERING
9.2.3 Pile Foundation Design
9.2.3.1 General
Methods based on engineering principles of varying degrees of sophistication are available as a
framework for pile design. All design procedures can be broadly divided into four categories:
(a)
(b)
(c)
(d)
Empirical 'rules-of-thumb',
Semi-empirical correlations with in-situ test results,
Rational methods based on simplified soil mechanics or rock mechanics theories, and
Advanced analytical (or numerical) techniques.
A judgment has to be made on the choice of an appropriate design method for a given project.
In principle, in choosing an appropriate design approach, relevant factors that should be considered
include:
(a)
(b)
(c)
The ground conditions,
Nature of the project, and
Comparable past experience.
9.2.3.2 Design Philosophies
The design of piles should comply with the following requirements throughout their service life:
• There should be adequate safety against failure of the ground. The required factor of safety
depends on the importance of the structure, consequence of failure, reliability and adequacy of
information on ground conditions, sensitivity of the structure, nature of the loading, local
experience, design methodologies, number of representative preliminary pile loading tests.
• There should be adequate margin against excessive pile movements, which would impair the
serviceability of the structure.
a) Global Factor of Safety Approach
The conventional global factor of safety approach is based on the use of a lumped factor applied
notionally to either the ultimate strength or the applied load. This is deemed to cater for all the
uncertainties inherent in the design.
9-6 March 2009