01 July 1997
(2) Vibratory Hammers. With vibratory hammers, this indicates the use of a high-frequency, low-
amplitude vibratory hammer. If these recourses fail, it may be necessary to adopt a method of foundation
installation other than pile driving. Vibratory hammers typically cause more ground vibration than impact
d. Obstructions. Where piles must penetrate ground containing numerous obstructions, use of jacked
or screwed piles generally is not attempted. However, open-end jacked piles can penetrate through
obstructions by the use of a chopping bit.
(1) Hammering. The usual procedure is to use a heavy pile with a driving tip and a heavy hammer
to try to force a way through the obstruction. This procedure invites damage to the pile and must be used
with caution and only when the pile section has been conservatively proportioned.
(2) Spudding. Another procedure is to use a spud. This is a section of heavy pile which is driven
through or past the obstruction and removed for reuse. Then the pile is inserted through the passage so
(3) Probing. If the group size and spacing permit, it is also feasible to probe for a way through or
past the obstructions. Use of a vibratory hammer, in which the pile can be readily extracted and reinserted
one or several times, may be a useful solution to this problem.
e. Limited Overhead Clearance. When operating in a situation where the overhead clearance is
limited, the use of a very short hammer, the use of special crane and leader arrangements, or the jacking of
piles in multiple sections may be required.
f. Selection of Pile. The type of pile depends upon a wide variety of factors, including soil type,
corrosion, local availability and cost, contractor preference, and the load bearing requirements of the
foundation. The various types of piles and their characteristics are given in chapter 1.
g. Selection of Pile Driving System. The selection of a pile driving system begins with the proper
selection of both the pile and the hammer. Generally speaking, the pile should be chosen first. If hammers
cannot be obtained following the criteria in section 2-1, then the pile should be altered to enable proper
equipment selection. The remainder of the system (crane, leaders, etc.) should be configured around the
hammer requirements. The hammer should be changed if the resultant rig is either unavailable or
(1) Preliminary Analysis. The selection of a pile driving hammer is a process that has several
stages and requires careful analysis.
(a) Quick Guide to Hammer Type. A quick guide to the selection of various types of pile driving
equipment is shown in table 2-1. As with any method of this sort, this is only a guide; specific jobsite
circumstances may warrant use of other methods. Beyond this generalization, the sizing of a particular pile
driver is different, depending upon whether the hammer is impact or vibratory.
(b) Pile Resistance Computation. Virtually any analysis of the hammer/pile system to
determine drivability will require a computation of the soil resistance. Methods used for such a computation
are given in TM 5-809-7. The information computed should include the soil type(s) encountered, resistance
for the pile shaft, toe, and, in the case of hollow piles, the inner shaft resistance. For the wave equation, the
distribution of the shaft resistance should also be noted.