EI 02G001
CEMP-E
01 July 1997
Table 3-1. Strengths and Weaknesses of Impact Hammer Types.
Hammer
Type
Description
Advantages
Disadvantages
External Combustion Hammers
Drop Hammer
Hammer is raised by a rope
Allows greater variation in
Very low frequency of
running over the top of a
both weight and speed of
blows.
framework and extending
blows.
back to a drum or geared
shaft; blow is delivered by
Low initial cost and
Efficiency reduced
the fall of the hammer
relatively long service life.
due to drag of rope and drum.
under influence of gravity.
Simple to operate in
Cannot be inverted and
remote locations where
used as a pile extractor
other equipment is
not obtainable.
Cannot be used in
locations where
headroom is limited.
Not readily adaptable for
driving batter piles.
Good performance.
Single-Acting
Steam or air raises the
Relatively low (50-60 blows
Air/Steam
movable mass of the
Simple in design and
per minute) blow rate.
hammer, which drops
dependable in service.
by gravity.
Usable in all soil conditions,
Cannot be used
but particularly effective in
as an extractor.
penetrating heavy clays.
Double-Acting
Steam or air raises
High frequency (90-150
Relatively high impact
Air/Steam
the striking part and
blows per minute) of
velocity results in pile
also impacts additional
blows keeps pile
head deformation of
energy during
moving and speeds
low compressive
downstroke.
penetration.
strength piles.
Can be used in
Large compressor or
horizontal position.
boiler required
for operation.
Works best in sandy soil,
but can be used in any
Rebound effects
soil.
make hammer
energy output variable
Can be inverted and used
as a pile extractor.
Enclosed ram permits
underwater driving.
3-10
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