Geotechnical Engineering

DHARM

850 GEOTECHNICAL ENGINEERING

which may be of timber grillage or cork. The foundation may be placed directly on soil or on a
suitable elastic layer, the purpose of which is to isolate the vibration and minimise the harmful
effects of the impact.

Tu p Frame

Anvil

Foundation

Elastic pad

(timber grillage or cork)

Elastic layer

R.C. trough

Fig. 20.29 Schematic of a typical hammer foundation (IS:2974-1980)
The frame of the hammer may either rest directly on the foundation or it may be sup-
ported from outside depending on the convenience. The frame is essentially to guide the ram
and house the arrangement for the movement of the ram.

The practice of design of the foundation for hammers has been to provide a massive
block foundation.

20.6.1Special Considerations

The following are the special considerations in planning the foundation for impact machines:

(i) The centre line of the anvil and the centroid of the base area should lie on the verti-

cal line passing through the common centre of gravity of the machine and its foun-

dation.

(ii) Where elastic pad is used under the anvil and the base of the foundation, care should

be taken to ensure uniform distribution of loading and protection of the pad against

water, oil, etc. It is recommended that the foundation be laid in a reinforced con-

crete trough formed by retaining walls on all sides. The foundation may be sepa-

rated from the side walls by means of an air gap.

(iii) If timber is used for elastic pad, the timber joists should be laid horizontally in the

form of a grillage. The joists must be impregnated with preservative for protection

against moisture.

(iv) The thickness of the elastic pad is governed by the permissible stresses in the re-

spective materials. Guidelines in this regard are given in Table 20.4 (Major, 1962):