Pile Design and Construction Practice, Fifth edition

306 Piles to resist uplift and lateral loading
Dock flooded
Piles acting neutrally
Ground-water level
Dock empty
All piles in tension
Ship under
construction
Piles in bending
and compression
Figure 6.1 Tension/compression piles beneath floor of shipbuilding dock.
Zone
of dessicated
soil
Tree removed
Roots left to decay
Uplift on
pile in this
zone
Pile anchored
against uplift
in this zone
Figure 6.2 Uplift on pile due to swelling of soil after removal of mature tree.
Piles in
compression
Compressible layer
described in Section 9.4. Floating ice on lakes and rivers can jam between piles in groups
causing them to lift when water levels rise or when the ice sheet buckles.
The most frequent situation necessitating design against lateral and uplift forces occurs
when the piles are required to restrain forces causing the sliding or overturning of structures.
Lateral forces may be imposed by earth pressure (Figure 6.3a), by the wind (Figure
6.3b), by earthquakes, or by the traction of braking vehicles (Figure 6.3c). In marine structures
lateral forces are caused by the impact of berthing ships (Figure 6.4), by the pull from
mooring ropes, and by the pressure of winds, currents, waves, and floating ice. A vertical
pile has a very low resistance to lateral loads and, for economy, substantial loadings are
designed to be resisted by groups of inclined or raking piles (sometimes referred to as ‘batter’
piles). Thus in Figure 6.5 the horizontal force can be resolved into two components,
producing an axial compressive force in pile A and a tensile force in pile B. It is usual to
ignore the restraint offered by the pile cap; thus the magnitude of each component is