Pile Design and Construction Practice, Fifth edition

Resistance of piles to compressive loads 153

Failure surface in

shaft friction

Failure surface

in end bearing

Figure 4.3Failure surfaces for compressive loading on piles.

300

250

200

150

100

50

0

1 5 10 50

30

25

20

15

10

Bearin

g ca

pacit

y^ (

tons

)

Bearing capacity (kN)

5

100

Time after driving (days)

200 × 215 mm concrete

(Gothenburg)

300 × 125 mm I-Beam

(Gothenburg)

350 × 150 mm tapered timber (Drammen)

150 mm (6 in) steel tube (San Francisco)

500 1000

Figure 4.4Gain in bearing capacity with increasing time after driving of piles into soft clays.

A further simplifying assumption is made that is proportional to the vertical effective
overburden pressure. Thus

(4.6)

The value of Kis 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 Kis 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 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, Kis low as the

(^) vo
s K vo tan (^) r
vo
h