Pile Design and Construction Practice, Fifth edition

248 Pile groups under compressive loading
Values of the shape factors s c and s � for centrally applied vertical loading are obtained
from Figure 5.7, and s q from the equation:
s q � s c(s c � 1)
N q
(5.2)
Inclined loading is considered in relation to the effective breadth B� and the effective
length L� of the equivalent block foundation. The plan dimensions of the block, as derived
by Meyerhof (5.5) , are shown in Figure 5.8. Thus for loading in the direction of the breadth:
B��B – 2e x
where e x is the eccentricity of loading in relation to the centroid of the base.
Similarly,
L��L – 2e y
The shape factors s are modified for inclined loading by the equations:
(5.3a)
(5.3b)
s CB � 1 �0.2i CB B�/L� (5.4)
s CL � 1 �0.2i CL L�/B� (5.5)
s qB � 1 �sin �i qB B�/L� (5.6)
s qL � 1 �sin �i qL L�/B� (5.7)
s �B � 1 – 0.4i �B B�/L� (5.8)
s � L � 1 – 0.4i �L L�/B� (5.9)
Where B� is less than L�, approximate values of the shape factors for centrally applied
vertical loading which are sufficiently accurate for most practical purposes are
Shape of base s c s q s �
Continuous strip 1.0 1.0 1.0
Rectangle 1�0.2 B/L 1�0.2 B/L 1–0.4 B/L
Square 1.3 1.2 0.8
Circle (diameter B) 1.3 1.2 0.6
Values of the depth factor d c are obtained from Figure 5.9. The values on the right-hand
side of the figure are for D � infinity. d q is obtained from
d q � d c � 1
N q
(5.10)
The depth factor d � can be taken as unity in all cases, also when � � 0 º , d q � 1.0. Where
� is greater than 25 º d q can be taken as equal to d c. A simplified value of d c and d q where �
is less than 25 º is 1�0.35 D/B. The use of the depth factors assumes that the soil above
foundation level is not significantly weaker in shear strength than that of the soil below this
level. However, in the case of pile groups, the piles are usually taken down through weak
soils into stronger material, when either the depth factors should not be used or the depth