Pile Design and Construction Practice, Fifth edition

246 Pile groups under compressive loading

Point of application

of resultant vertical

force V

Centroid of

foundation Equivalent base of area A 9

= B 9 × L 9

Pressure distribution

on equivalent base

= (^) B 9 × L 9
Eccentricity applied
vertical load
Eccentricity with
respect to centroid
of foundation
Inclined load
V
ey L
ex
ex ex
=B– 2 ex
B 9 =B– 2 ex
B 9
B
L^9
=^
L–
2 e
y
v
B 9
R
Figure 5.8Transformation of eccentrically-loaded foundation to equivalent rectangular area carring
uniformly distributed load.
0.5 0 0.2 0.4
Breadth/length, B/L
0.6 0.8 1.0
0.6
0.8
Shape factor,
s
Shape factor,
sc
1.0
1.2
1.4
1.6
2.0
1.8
f=45°
=40°
=35°
=30°
=30°
=35°
=0– 25 °
=0– 25 °
= 40°
= 45°
Figure 5.7Shape factors scand s(after Brinch Hansen(5.4)).
The equation in similar form is given in EC7, Annex D, but the third term and the depth
factors have been omitted, in the latter case because the application of the Eurocode is essentially
for shallow spread foundations (Dnot greater than B). When applied to the block foundation
equivalent to a pile group, the depth of the group could be large relative to its width. Thus by
omitting the depth factors the value of qucould be over-conservative. The use of equation 5.1
in checking for compliance with the EC7 recommendations is described in Section 5.4.