very sensitive to the values of the angle of shearing resistance of the soils. These values are
obtained from in-situ tests made in boreholes, and if the boring method has loosened the
soil, which can happen if incorrect techniques are used (see Section 11.1.4), then the base
resistance of any form of driven pile is grossly underestimated. It is very unlikely that the
boring method will compact the soil, and thus any over-estimation of the shearing resistance
is unlikely.
A reliable method of predicting the shaft friction and base resistance of driven and driven
and cast-in-place piles is to make static cone penetration tests at the site investigation stage
(see Section 11.1.4). This equipment produces curves of cone penetration resistance with
depth (Figure 4.18). Extensive experience with pile predictions based on the cone
penetrometer in the Netherlands has produced a set of design rules which have been
summarized by Meigh(4.25).
176 Resistance of piles to compressive loads
Load on pile (kN)Settlement of pile head (mm)01020(^30) 480 mm
bored pile
4.6 m long
480 mm bored pile
9.1 m long
Sandy clay fill
Soft clayey
peat with
pockets of
silty fine sand
Dense medium
sand and
gravel
(N= 47)
Very dense silty
fine sand and
gravel (N= 86)
Very dense silty
fine sand
with thin layers
of silty clay
(N= 70)
Stiff laminated
silty clay with
partings of
silty fine sand
10.06
Borehole
record
10.36
5.49
2.74
0.91
6.40
510 mm dia precast
concrete pile
driven to 4.0 m
40
50
60
70
80
90
200 400 600 800
Figure 4.17Comparison of compressive resistance of driven piles and bored and cast in-situ piles in
dense to very dense coarse soils.