Geotechnical Engineering

DHARM

ELEMENTS OF SOIL DYNAMICS AND MACHINE FOUNDATIONS 851

Table 20.4 Thickness of timber pads under anvil (after Major, 1962)

Type of hammer Thickness of pad (m) for a falling weight of

upto 10 kN 10-30 kN 30 kN

Double acting drop hammers 0.2 0.2 to 0.6 0.6 to 1.2

Single acting drop hammers 0.1 0.1 to 0.4 0.4 to 0.9

Forge hammers 0.2 0.2 to 0.6 0.6 to 1.00

(v) When two adjacent foundations are laid at different depths, the straight line con-

necting edges should form an angle not exceeding 25º to the horizontal (Fig. 20.30).

However, if foundation are too close, they may be laid to the same depth and a

common raft provided as base.

20.6.2Design Data

The following data are required to be supplied to the designer:

(i) Type of hammer (ii) Weight of falling tup (Wt)

(iii) Weight of anvil (Wa)

a

a

Adjacent

foundation

Machine

foundation

Anvil

Adjacent

foundation

Fig. 20.30 Criteria for locating adjacent foundations (IS: 2974-Pt II-1980)

(iv) Weight of the hammer stand supported on the foundation (Wf), to be added to Wa

only if the stand is directly resting on the foundation

(v) Base area of anvil (La × Ba)

(vi) Stroke or fall of hammer (h)

(vii) Effective working pressure (p) on the piston and area of piston (a)

(viii) Outline of the foundation showing the position of anchor bolts, floor level, position

of adjacent foundations, etc.

20.6.3Elastic Pad Under the Anvil

The thickness of elastic pad varies with the weight of the dropping parts and the type of
hammer from about 200 mm for 10 kN hammer to a maximum of about 200 mm for hammers
of over 30 kN (Table 20.4).

The thickness of the pad should be so selected that the dynamic stresses induced in the
pad by impact do not exceed the permissible values, which are as follows (Barkan, 1962):

Oak : 30,000 to 35,000 kN/m^2