01 July 1997
compression, tension or uplift, negative skin friction from compaction or consolidation of adjacent soil, and
(e) Specifications should include provision for contractor and Government responsibilities
when using PDA equipment. The PDA may be useful to indicate hammer efficiency, driving energy
delivered to the pile, driving stresses, pile capacity, and possible damage to the pile. However,
measurements may be distorted because of residual stresses in the pile and soil freeze or relaxation effects.
(2) Installation Equipment. Specifications will detail requirements of the pile driving system.
(a) Minimum and maximum energy of the hammer will be specified. The minimum energy is
required to be sure that the pile capacity will be properly indicated by the penetration resistance. Hammers
that are too light can indicate low displacements/blow without any significant penetration and capacity. The
maximum energy is required so that the piles will not be damaged by driving with a hammer that is too large.
(b) Requirements for driving helmets, caps, and hammer and pile cushions will be specified.
Cushions that are too soft will absorb too much energy and driving may stall. Cushions that are too hard will
cause hammer or pile damage. Commonly used materials for hammer cushions are hardwood, plywoods,
woven steel wire, laminated micarta and aluminum discs, and plastic laminated discs. Laminated materials
provide superior energy transmission characteristics, maintain their elastic properties uniformly during
driving, and have a relatively long useful life. Commonly used pile cushions are plywood and oak board.
Engineering experience combined with wave equation analysis is recommended for selecting the cushion
materials and thickness.
(c) Specifications will describe the piles selected for the project.
(d) Specifications should clearly define the basis of hammer approval (e.g., by results of wave
equation analysis) and state criteria that will be used to establish the penetration limits. Installation
equipment or methods suspected of compromising the pile foundation should be clearly excluded from the
specifications. The contractor may question these exclusions and may substantiate any claim at the
contractor' expense by performing an independent wave equation analysis, field verification of driving and
static load tests, dynamic monitoring, or other methods designated by the designer.
(3) Pile Installation. Specifications will describe the piles selected for the work and how the piles
will be driven.
(a) Care and handling of piles will be specified to avoid overstressing. Sweep (camber)
limitations will be specified because excessive sweep can cause piles to be driven out of tolerance. For
example, sweep may be limited to 2 inches for steel H-piles. The required number and locations of
permissible pick-up points on the pile will be clearly indicated in the specifications. Loading and unloading of
long steel piles should be done by supporting at a minimum of two points about one-fourth length from the
ends of the pile. Precast concrete piles should be supported at several points when they are lifted to the
driving position. Any deviations from the specifications must be approved by the design engineer.
(b) Type of lead, whether fixed or swinging, shall be specified to assure adequate alignment.
Driving tolerances will be specified to assure adequate positioning and vertical alignment. A lateral deviation
from the specified location at the pile head of not more than 3 to 6 inches measured horizontally and a final
variation in alignment of not more than 0.25 inch/foot measured along the longitudinal axis should normally
be permitted. A deviation of 1 inch from the specified cutoff elevation is reasonable. These
recommendations are for large pile groups and should be verified for specific projects.
(c) Splices will be specified if these are required.