Pile Design and Construction Practice, Fifth edition

Figure 4.3 Failure surfaces for compressive loading on piles.
Bearing capacity (kN)
300
250
200
200 × 215 mm concrete
(Gothenburg)
Resistance of piles to compressive loads 153
Failure surface in
shaft friction
Failure surface
in end bearing
150
15
100
350 × 150 mm tapered timber (Drammen)
10
50
0
300 × 125 mm I-Beam
(Gothenburg)
150 mm (6 in) steel tube (San Francisco)
5
1 5 10 50
Time after driving (days)
100
500 1000
Figure 4.4 Gain in bearing capacity with increasing time after driving of piles into soft clays.
A further simplifying assumption is made that ��h is proportional to the vertical effective
overburden pressure . Thus
� s � K�� vo tan � r
�� vo
30
25
20
Bearing capacity (tons)
(4.6)
The value of K is constantly changing throughout the period of installation of the pile and
its subsequent loading history. In the case of a driven pile in a stiff clay K is initially very
high, as a result of the energy transmitted by the hammer blows required to displace the clay
around the pile. However, at this time �� vo is very low or even negative due to the high
pore-water pressures induced by the pile driving. In the case of a bored pile, K is low as the