Geotechnical Engineering

DHARM

668 GEOTECHNICAL ENGINEERING

Here, C = C 1 + C 2 + C 3

C 1 = temporary compression of dolly and packing

= 1.77

Q

A

up,

where the driving is without dolly or helmet and cushion about 2.5 cm thick,

C 1 = 9.05

Q

A

up,

where the driving is with short dolly up to 60 cm long helmet and cushion up to 7.5 cm thick.

C 2 = temporary compression of pile

= 0.0657

QL

A

up

C 3 = temporary compression of ground

= 3.55

Q

A

up

L = length of pile in metres

A = area of cross-section of pile in cm^2.

This is applicable for friction piles.

For point-bearing piles, a value di 21 Wp is substituted for Wp. The value η. H is also

referred to as the effective fall of hammer.

Danish formula

The Danish formula is

Qup =

WH

ss

h

o

..η

F +

HG

I

KJ

1

2

...(Eq. 16.27)

where so = elastic compression of the pile

so =

2 WHL

AE

h ...(Eq. 16.27a)

Here L, A and E refer to the length, area of cross-section, and modulus of elasticity of
the pile.

A factor of safety of 3 is recommended for use in conjunction with this formula. Com-
ments on the use of dynamic pile-driving formulae:

1. In general, dynamic pile driving formulae appear to be more applicable to piles
   driven into cohesionless soils. However, Vesic (1967) suggests that the value of C in
   Engineering News formula should be taken 1 cm for steel pipe piles and 1.5 cm for
   precast concrete piles, since the results would otherwise be too conservative.


2. According to Vesic (1967), Hiley’s formula does not give consistent results for piles
   in cohesionless soils.


3. A basic objection to the use of these formulae is that dynamic resistance of a soil is
   very much different from its static resistance. However, formulae such as the