Pile Design and Construction Practice, Fifth edition

(a)
determining the compressive and tensile forces in the piles by a triangle of forces assumes
that the piles are hinged at their point of intersection and that the lateral loads are carried
only in an axial direction by the piles. The tension pile will develop its maximum pull-out
resistance with negligible movement, and the yielding of a properly designed compression
pile of small to medium diameter is unlikely to exceed 10 mm at the working load. Thus the
horizontal deflections of the pile cap will be quite small.
For economy, the raking piles should be installed at the largest possible angle from
the vertical. This depends on the type of pile used (see Section 3.4.11). Where raking piles
are embedded in fill which is settling under its own weight (Figure 6.38a) or in a
compressible clay subjected to a surcharge load or to superimposed fill (Figure 6.38b) the
vertical loading on the upper surface of the rakers may induce high bending moments in the
pile shaft. Because of this, raking piles may not be an appropriate form of construction in
deep fill or compressible layers.
6.5 Lateral loads on groups of piles
(b)
Filling setting under its
own weight
Vertical pressure
on piles
Piles to resist uplift and lateral loading 353
Compressible
soil
Figure 6.38 Bending of slender raking piles due to loading from soil subsidence (a) Fill settling
under own weight (b) Fill overlying compressible soil.
Loads on individual piles forming a group of vertical piles that is subject to horizontal
loading or to combined vertical and horizontal loading can be determined quite simply (for
cases where the resultant cuts the underside of the pile cap) by taking moments about the
neutral axis of the pile group. Thus in Figure 6.39 the vertical component V of the load on
any pile produced by an inclined thrust R, where R is the resultant of a horizontal load H and
a vertical load W is given by
V � (6.54)
where W is the total vertical load on the pile group, n is the number of piles in the group, e
is the distance between the point of intersection of R with the underside of the pile cap and
the neutral axis of the pile group, and x¯ is the distance between the pile and the neutral axis
of the pile group (x¯ is positive when measured in same direction as e and negative when in
the opposite direction).
W Wex
n �
2
�x