Pile Design and Construction Practice, Fifth edition

354 Piles to resist uplift and lateral loading
Point of application of
horizontal thrust
Neutral axis of
pile group +x –x
R
H
X
e
Determination of the individual loads on groups of raking or combined raking and
vertical piles is a complex matter if there are more than three rows of piles in the group. The
latter case can be analysed by static methods if it is assumed that the piles are hinged at their
upper ends, that horizontal loads are carried only by axial forces in the inclined piles and
that vertical piles do not carry any horizontal loading. The forces in the piles are resolved
graphically as shown in Figure 6.40. The same method can be used if pairs of piles or
individual groups of three closely spaced piles are arranged in not more than three rows, as
shown in Figure 6.41. To produce the parallelogram of forces the line of action of the forces
in the piles is taken as the centre-line of each individual group.
The determination of the individual loads on piles installed in groups comprising multiple
rows of raking or combined raking and vertical piles is a highly complex process which
involves the analysis of movements in three dimensions; i.e. movements in vertical and
horizontal translation and in rotational modes. The analysis of loadings on piles subjected to
these movements requires the solution of six simultaneous equations, necessitating the use
of a computer for practical design problems.
The reader is referred to the work of Poulos and Davis (6.25) , and Poulos (6.26) for an account
of their research into the behaviour of laterally loaded pile groups in an elastic medium.
Randolph (6.23) gives expressions to determine the interaction factor between adjacent piles
in groups carrying compression and lateral loading and compares them with values derived
W
Point of application of
resultant load on
underside of pile cap
Figure 6.39 Calculating load distribution on group of piles carrying vertical and horizontal loading.