Pile Design and Construction Practice, Fifth edition

and divided it by the appropriate safety factor, it is still necessary to check that the
permissible deflection of the pile is not exceeded.
There are many inter-related factors which govern the behaviour of laterally loaded piles.
The dominant one is the pile stiffness, which influences the deflection and determines
whether the failure mechanism is one of the rotation of a short rigid element, or is due to
flexure followed by the failure in bending of a long pile. The type of loading, whether
sustained (as in the case of earth pressure transmitted by a retaining wall) or alternating (say,
from reciprocating machinery) or pulsating (as from the traffic loading on a bridge pier),
influences the degree of yielding of the soil. External influences such as scouring around
piles at sea-bed level, or the seasonal shrinkage of clay soils away from the upper part of the
pile shaft, affect the resistance of the soil at a shallow depth.
Methods of calculating ultimate resistance and deflection under lateral loads are presented
in the following sections of this chapter. No attempt is made to give their complete theoret-
ical basis. Various simplifications have been necessary in order to provide simple solutions
to complex problems of soil–structure interaction, and the limitations of the methods are
stated where these are particularly relevant. Most practical calculations are processes of trial

328 Piles to resist uplift and lateral loading

Fracture

L L

He H

Fracture

(a) (b)

Figure 6.19Long vertical pile under horizontal load (a) Free head (b) Fixed head.

Load H

e

L

Centre of

rotation

H

L

(a) (b)

Figure 6.18Short vertical pile under horizontal load.