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

Chapter 9 FOUNDATION ENGINEERING
E pe = equivalent Young’s modulus of the pile = 4E pI p
r o
4
For a given problem, iterations will be necessary to evaluate the values of L c and G c . Expressions for
deflection and rotation at ground level given by Randolph's elastic continuum formulation are
summarised in Figure 9.14.
Results of horizontal plate loading tests carried out from within a hand-dug caisson in completely
weathered granite (Whiteside, 1981) indicate the following range of correlation:
E h ' = 0.1 N to 1.9 N (MPa) (9.26)
where E h ' is the drained horizontal Young's modulus of the soil.
The modulus may be nearer the lower bound if disturbance due to pile excavation and stress relief is
excessive. The reloading modulus was however found to be two to three times the above values.
Plumbridge et al (2000b) carried out lateral loading tests on large-diameter bored piles and barrettes
in fill and alluvial deposits. Testing arrangement on five sites included a 100 cycle bi-directional
loading stage followed by a five-stage maintained lateral loading test. The cyclic loading indicated
only a negligible degradation in pile-soil stiffness after the 100 cycle bi-direction loading. The
deflection behaviour for piles in push or pull directions was generally similar. Based on the deflection
profile of the single pile in maintained-load tests, the correlation between horizontal Young's
modulus, E h ' and SPT N value was found to range between 3 N and 4 N (MPa).
Lam et al (1991) reported results of horizontal Goodman Jack tests carried out from within a caisson
in moderately to slightly (Grade III / II) weathered granite. The interpreted rock mass modulus was
in the range of 3.1 to 8.2 GPa.
In the absence of site-specific field data, the above range of values may be used in preliminary
design of piles subject to lateral loads.
Free-head Piles
δ h = E p/G c 1
7
0.27H
+ 0.3M
ρ c 'G c 0.5L c 0.5L c 2
Ө = E p/G c 1
7
0.3H
+ 0.8 'M
ρ c 'G c . 0.5L c 3
The maximum moment for a pile under a lateral load H occurs
at depth between 0.25L c (for homogenous soil) and 0.33L c
(for soil with stiffness proportional to depth). The value of the
maximum bending moment M max may be approximated using
the following expression:
M max = 0.1 H L c
ρ c '
Figure 9.13 Analysis of Behaviour of a Laterally Loaded Pile Using the Elastic Continuum Method
(Randolph, 1981a)
9-44 March 2009