01 July 1997
(b) Anvils and Helmets. Anvils and helmets must be of a construction that will withstand the high
loads and stresses of impact pile driving. They should be inspected thoroughly before use. Any helmet or
anvil that has any cracks, broken pieces, or thin wall sections that might break in use should be rejected
before driving begins. During use, a cap should be inspected frequently for developing cracks or broken or
missing pieces, and removed from the job if any of these is discovered during inspection.
(c) Mandrel. Mandrels also transmit high loads. They should be inspected during use for any
cracks or other mechanical failures, and these should be repaired before driving is resumed.
b. Hammer Operation. There are several important performance parameters to monitor during driving.
(1) Hammer Stroke. The single most important parameter to look for is the stroke of the ram.
(a) Single Acting Hammers. With single acting hammers of any kind, the only source of
energy for the ram on the downstroke is its drop through the gravity field. So it is absolutely essential that its
stroke be what is required by the piling being driven, whether that be full or partial stroke. This stroke
should be achieved when the pile is at refusal; some hammers (especially diesel hammers) cannot achieve
full stroke without the pile energy rebound of refusal driving.
(b) Other Impact Hammers. Although the stroke is not as important with hammers that have
assistance on the downstroke, it is important to establish what stroke is required for the particular job.
(c) Monitoring of Stroke. If the ram is visible from the outside of the hammer, then visual
monitoring of the stroke is possible. With air/steam hammers, as the ram moves it wipes most of the
lubricant off of the columns. The length of this wiped area will determine the stroke of the hammer. With
open-end diesel hammers, a striped pole can be mounted on top of the hammer. As the ram raises up, the
stroke can be determined by comparing the maximum height of the ram with the highest point of the ram
(2) Speed. Although the hammer speed is a general indicator of the performance of the
hammer, except for single-acting diesel hammers, it cannot be used to determine the energy output of the
hammers. This is because there are simply too many variables influencing the motion of the ram,
especially the variations in energy rebound from the pile. With single-acting diesel hammers, devices exist
that can estimate the energy of the hammer based on its blow rate.
(3) Pressure. With external combustion hammers, the pressure of the operating fluid is important
in the energy output of the hammers. With single-acting hammers, although no direct correlation can be
made between pressure and output energy, monitoring the pressure can be a useful tool in diagnosing
problems with the driving system. For other hammers, fluid pressure of the motive fluid or trapped dashpot
air is part of the downstroke assistance and is an important factor in hammer energy. For proper readings,
any pressure readings should be taken at the hammer by a pressure gauge at the hammer or by remote
(4) Direct Energy Monitoring. If the ram is not visible, or for more complete information on the
energy output of the hammer, devices exist that can determine the energy output of the hammer, either
from the hammer itself or after the stress wave has passed through the cushion material and drive cap.
These can be either obtained from the manufacturer or third-party vendors and consultants. It is very
important that these devices be properly installed, calibrated, and operated by experienced and trained
personnel who are very familiar with their use; incorrect installation, calibration, or operation can result in
erroneous readings. Complete reports on the use of these devices should be required if they are used.