01 July 1997
MONITORING OF PILE INSTALLATION
4-1. EQUIPMENT OPERATION. Successful pile driving is dependent upon both the condition of the
equipment and the operating technique used. Failure to observe the proper procedures with the
equipment can result in loss of energy imparted to the pile, failure to reach the desired penetration
depth, property damage, personal injury, and equipment breakdowns, which lead to downtime, job
delays, and contract disputes.
a. Condition of Equipment. Equipment should be maintained and operated in accordance with
manufacturer' recommendations. This includes proper preparation of the equipment, correct setup
before driving, good operation during driving, and proper transport and storage procedures.
(1) Hammer. The hammer is the element that directly interfaces with the pile. Thus, it
transmits and receives the most vibration and impact during driving. Although most pile drivers in use
today are relatively simple machines, attention to their basic maintenance is still important. It is also
essential that this equipment, in common with most construction equipment, must be operated by
personnel with the proper training and experience in the use of the equipment.
(a) Impact Hammers. The most important element in the efficient operation of impact
hammers is proper lubrication. All wear surfaces must be kept lubricated by the means provided for
either on the machine or from the outside. Typical lubrication points for an air/steam hammer are
shown in figure 4-1. Diesel hammers vary widely in their lubrication systems, but the entire cylinder
assembly must be lubricated in its full length, whether by grease or oil. Hydraulic impact hammers are
similar to air/steam hammers except for the hydraulic system and cylinder(s). In these cases, their
maintenance is more like that of a vibratory hammer (see next section). Also, due to the high loads
during ram deceleration and pile rebound, impact hammers are subject to dynamic stresses. All
fasteners must be kept tight, and parts which are worn, cracked, or broken must be replaced.
(b) Vibratory Hammers. A chart of basic items to watch for with vibratory hammers is
shown in table 4-1.
(2) Driving Cap. The driving cap transmits the impact force from the hammer to the pile. Its
proper setup and maintenance are central to successful pile driving.
(a) Cushion. Both hammer and pile cushion material should be configured and installed so
that there is adequate cushioning for the ram and the pile. Materials which are too hard, or less than
complete cushion stacks must be avoided; cushions which are added piece by piece during driving must
also be avoided. Cushion material is an expandable item; it degenerates during its life with heat and
plastic deformation; it is essential that it is replaced when it is burnt or deformed to its compressive limit.
Cushion whose stack height is 75 percent of the original, uncompressed height should be replaced.
Also, when piling are designed using the wave equation analysis, it is essential that the cushion
configuration assumed during the wave equation analysis be a realistic one in the field and that the
configuration assumed during the analysis be replicated in the field. This is especially important with a
concrete pile cushion; inadequate cushion may lead to tension cracking during driving and excessive
material may lead to unanticipated energy losses. If the pile cushion is plywood and the pile concrete, a
new pile cushion should be used with every pile.