Geotechnical Engineering

DHARM

ELEMENTS OF SOIL DYNAMICS AND MACHINE FOUNDATIONS 857

where nf = ratio of the weight of the foundation (Wf) to that of the dropping weight or tup (Wt)

or (Wf/Wt)

e = coefficient of restitution,

v = velocity of the dropping weight just before impact, (meters/sec)

and na = ratio of the weight of anvil (Wa) to that of the dropping weight (Wt) or

W

W

a

t

F

HG

I

KJ

.

Numerical values of some hammer coefficients are given in Table 20.6:

Table 20.6 Values of some hammer coefficients (after Barkan, 1962)

Type of Hammer v(m/s) e na nf

Stamping hammers:

Double acting (Stamping of steel) 6.5 0.5 30 48

Single-acting (Stamping of steel) 4.5 0.5 20 34

Single-acting (Stamping of non-ferrous metals) 4.5 0.0 ... 16

Forge hammers:

Double-acting 6.5 0.25 30 35

Single-acting 4.5 0.25 20 25

Weight of the foundation can now be got by multiplying the value of nf obtained from
Eq. 20.111 by the weight of the falling tup, as this and the weight of the anvil would have been
decided earlier.

Base Area of the Foundation Block

af =

20 1()+ev

qa ...(Eq. 20.112)

where af = ratio of the base area of the foundation block (A) to the weight of the dropping

weight (Wt) or

A

Wt

F

HG

I

KJ

,

and qa = allowable bearing pressure of soil.

Values of af have been found to vary from 2 to 13 for different types of hammers resting
on a variety of soils of different strengths.

The required base area of the foundation block may be got by multiplying the value of af
obtained from Eq. 20.112 by the weight of the falling tup.

It is important to note that Equations 20.111 and 20.112 are not dimensionally correct;
therefore, these equations shall be used with the weight, length, and time expressed in tonnes,
metres, and seconds, respectively, the units in which Barkan derived them.

20.6.9Minimum Thickness of Foundation

The minimum thickness of the foundation below the anvil for different weights of hammer, as
recommended by Major (1962) are given in Table 20.7: