Geotechnical Engineering

DHARM

856 GEOTECHNICAL ENGINEERING

In this connection Barken gives the following equation:

Cu′ = kcCu ...(Eq. 20.110)

where Cu′ = coefficient of elastic uniform compression to be used in the design of hammer

foundation,

Cu = coefficient of elastic uniform compression of the soil obtained from tests,

and kc = a correction coefficient.

Barkan (1962) recommends a value of 3 for kc for use in the design of hammer founda-

tions, based on the observations in the extensive experimental program carried out by him.

20.6.6Design Criteria
The following are the primary criteria for the design of a hammer foundation:
(i) The amplitudes of the foundation block and anvil should not exceed the permissible
values given hereunder:

For the Foundation Block (A 1 )

The maximum amplitude of the foundation should not exceed 1.2 mm. In the case of founda-

tions resting on sand below ground water table, this should be limited to 0.8 mm.

For the Anvil (Aa)

The permissible amplitudes which depend upon the weight of the falling tup are given in Table

20.5:

Table 20.5 Permissible amplitudes for anvil (After Barkan, 1962)

Weight of tup (Wt) upto 10 kN 20 kN 30 kN

Maximum permissible 1 mm 2 mm 3 to 4 mm

amplitude

(ii) The maximum stresses in the soil and other elastic layers shall be less than the
permissible values for the respective materials. If timber is used for the elastic pad, the per-
missible stresses given in subsection 20.6.3 are to be considered.

20.6.7Design Approach

The design is a trial and error process. Certain dimensions are assumed for the foundation

block and elastic pad. The stress in the elastic pad, and the amplitudes of motion are calcu-

lated. These values are compared with the respective permissible values, and if necessary, the

dimensions are changed, and the analysis revised.

20.6.8Barkan’s Empirical Procedure

Based on his experimental investigations, Barkan (1962) recommended the following empiri-

cal equations for the determination of the tentative weight of the foundation and the base area

of the foundation block in terms of the coefficient of restitution and the velocity of the dropping

parts:

Weight of Foundation

nf = [8.0(1 + e)v – na] ...(Eq. 20.111)