Geotechnical Engineering

DHARM

PILE FOUNDATIONS 667

(ii) Elastic compression of pile cap (c 2 )

Table 16.5 c 2 values

Material of pile Driving stress (kN/m^2 ) Value of c 2

Precast concrete pile with packing at head 3000 to 15000 0.12 to 0.50

Steel H pile 3000 to 15000 0.04 to 0.16

Timber pile without cap 3000 to 15000 0.05 to 0.20

(iii) Elastic compression of soil (c 3 )
The average value is taken as 0.1 cm (it may range from 0 for hard soil to 0.2 for soft
soil).

(iv) Efficiency of hammer

Table 16.6 Hammer efficiencies

Type of hammer Efficiency of hammer

Drop hammer 1.00

Single-acting steam hammer 0.75 to 0.85

Double-acting steam hammer 0.85

Diesel hammer 1.00

(v) Coefficient of restitution (Cr)

Table 16.7 Cr-values

Material Value of Cr

Wood pile 0.25

Wood cushion on steel pile 0.32

C.I. Hammer on concrete pile without cap 0.40

C.I. Hammer on steel pipe without cushion 0.55

In I.S: 2911 (Part I)-1974 the Hiley-formula is given in a slightly different form:

Qup =

WH

sC

hbηη

(/)+ 2

...(Eq. 16.25)

where ηb = efficiency of hammer blow (or ratio of energy after impact to the energy of the

hammer before impact) ηb is given by

ηb =

WCW

WW

hrp

hp

+

+

F

H

G

I

K

J

2

, when W > CrWp ...(Eq. 16.26a)

=

WCW

WW

WCW

WW

hrp

h p

hrp

h p

+

+

F

H

G

I

K

J−

−

+

F

H

G

I

K

J

2 2

, when W < CrWp ...(Eq. 16.26b)