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

Chapter 9 FOUNDATION ENGINEERING
9.2.6.4 Recommendations on the Use of Dynamic Loading Tests
Traditionally, pile driving formulae are used as a mean to assess pile capacity from a measurement
of 'set per blow' and are supplemented with static loading tests on selected piles. Although such an
approach is the standard in local practice for driving piles, driving formulae are considered
fundamentally incorrect and quantitative agreement between static pile capacities predicted by
driving formulae and actual values cannot be relied upon.
Dynamic load testing is preferred for pile capacity predictions. Dynamic load testing can be
applied to non-homogeneous soils or piles with a varying cross-sectional area. The static loadsettlement
response of a pile can also be predicted.
Dynamic pile loading tests can supplement the design of driven piles provided that they have
been properly calibrated against static loading tests and an adequate site investigation has been
carried out. It should be noted that such calibration of the analysis model has to be based on
static loading tests on piles of similar length, cross section and under comparable soil conditions
and loaded to failure. A static loading test, which is carried out to a proof load, is an inconclusive
result for assessing the ultimate resistance of the pile.
The reliability of the prediction of dynamic loading test methods is dependent on the adequacy of
the wave equation model and the premise that a unique solution exists when the best fit is
obtained within the limitation of the assumption of an elasto/rigid plastic soil behavior. In
addition, there are uncertainties with the modelling of effects of residual driving stresses in the
wave equation formulation.
9.3 LATERALLY LOADED PILES
9.3.1 Introduction
The lateral load capacity of a pile may be limited by the following:
(a) Shear capacity of the soil;
(b) Structural (i.e. bending moment and shear) capacity of the pile section itself; and
(c) Excessive deformation of the pile.
The failure mechanisms of short piles under lateral loads as compared to those of long piles differ,
requiring therefore different and appropriate design methods. In order to establish if a pile behaves
a rigid unit (i.e. short pile) or as a flexible member (i.e. long pile), the stiffness factors as defined in
Figure 9.8 below will employed.
March 2009 9-29