Pile Design and Construction Practice, Fifth edition

4.5 Piles in layered fine- and coarse-grained soils

It will be appreciated from Sections 4.2 and 4.3 that piles in fine-grained soils have a
relatively high shaft friction and a low end-bearing resistance, and in coarse soils the reverse
is the case. Therefore, when piles are installed in layered soils the location of the pile toe is
of great importance. The first essential is to obtain a reliable picture of the depth and lateral
extent of the soil layers. This can be done by making in-situ tests with static or dynamic cone
test equipment (see Section 11.1.4), correlated by an adequate number of boreholes. If it is
desired to utilize the potentially high end-bearing resistance provided by a dense sand or

Resistance of piles to compressive loads 189

2.0 OD
tubular steel
pile with
closed end

Blows/250 mm penetration

Piles driven by Delmang D100

diesel hammer

Dense sandy

gravel and

cobbles

Delay time

in hours

45.6

Stiff sandy

silty clay

Dense sandy

clayey silt

Depth below sea level (m)

36

13

21

(^27812)
34.8
33.6

• 75


• 74


• 76


• 77


• 78
  800600400200

77.9

12

16

84

18

0

Figure 4.23Driving resistance over final 4.5 m of penetration for 2.0 m tubular steel pile showing reduc-
tion in driving resistance after various delay periods, New Galata Bridge, Istanbul.