Geotechnical Engineering

DHARM

PILE FOUNDATIONS 655

Leads

Pile

Stay

Air compressor or

steam generator

(a) Crawler-mounted crane rig

Leads

Hammer

(b) Sectional plan of leads

Hammer

Fig. 16.2 Pile driver with crawler-mounted crane rig

Pneumatic-tyred motor crane rigs are used for highway work; rail-mounted rigs are

available for railway work; and barge-mounted rigs are used for marine work.

Pile hammers are of the following types:

(i) Drop hammer

(ii) Single-acting hammer (steam or pneumatic)

(iii) Double-acting hammer (steam or pneumatic)

(iv) Diesel hammer (internal combustion)

(v) Vibratory hammer

Drop hammer

This is the simplest type. The hammer, ram or monkey is raised by pulley and which and
allowed to fall on the top of the pile.

The drop hammer is simple but very slow and is used for small jobs only.

Single-acting hammer

In this type, the hammer is raised by steam or compressed air and is allowed to drop on
to the pile head. The hammer is usually heavy and rugged, weighing 10 to 100 kN. The height
of fall may be about 60 to 90 cm. The blows may be delivered much more rapidly than in the
case of drop hammer.

Double-acting hammer
In this type, steam or air pressure is employed to lift the ram and then accelerate it downward.
The blows are more rapid; from 90 to 240 blows per minute, thus reducing the time required to
drive the pile, and making the driving easier. The weight of the ram may be 10 to 25 kN.

This type of hammer loses its effectiveness with wear and poor valve adjustment. The
energy delivered in each blow varies greatly with the steam or air pressure. If the number of
blows per minute is approximately the rated value, the pressure is probably correct.

Steam operation is more efficient, particularly with circulating steam generators. If the
hammer is to be operated under water, which is possible with enclosed double-acting types,
compressed air operation is necessary.