Pile Design and Construction Practice, Fifth edition

300 Pile groups under compressive loading

1200 mm bored

piles

0.00

9.50

16.50 10.5 m

12-storey building

Ground level

GWL

7.00

Soft organic

silty clay

48.75 18.75 Sand fill ( 2.1 mg/m (^3) )
3.75
Stiff to very
stiff clay
30 °
L 52.25
B 22.25
23.50
30.50
37.50
44.50
Cu 430 kN/m^2
mv 0.04 m^2 /MN
Ed 120 MN/m^2
Cu 90 kN/m^2
mv 0.08 m^2 /MN
Layer 2
Layer 3
Layer 4
Rock
L 60.25
L 68.25
L 76.25
B 38.25
B 46.25
B 30.25
qn 139 kN/m^2
( (^) sat 1.6 Mg/m^3 )
4.00
Ed 40 MN/m^2
Figure 5.45
Adopt a spacing of say 3.75 m in both directions. Thus the dimensions of the pile group are
5 3.75 18.75 m and 13 3.75 48.75 m.
Average load carried by piles
The central two rows of piles carry higher loads than the outer two rows on each side.
A likely loading for the centre rows is 2 200 kN per pile. The required penetration of the
piles will be calculated on this loading. The exterior piles will be taken to the same depth
but adopting a reduced diameter as required by the lesser loading.
The piles carry negative skin friction due to the consolidation of the soft clay under the
imposed loading of the sand fill. At 6 months, settlement of the soft clay will be continuing
at a very slow rate and it is appropriate to use Figure 4.39 to calculate the negative skin
friction in this layer.

48  21  160

14  6

1920 kN per pile