PILE DRIVING PROCESS
resistance factors) are achieved by this
complete testing process.
Perform final evaluation of driving
criteria for production piles. The results
of the static load testing are compared
with the results of the static analysis, the
wave equation analysis and the PDA. If
good agreement exists, the driving criterion
established for the test piles is then
adopted and used for all production piles.
If the static load test results do not
agree with the analyses, then the driving
criteria can be adjusted either upward
or downward. The driving criteria will
be adjusted upward if the load test
showed less capacity than required and
may be adjusted downward if the load
test showed more capacity. Slight adjustments
can easily be justified and verified
by additional wave equation analysis or
PDA tests. If the load test results are significantly
different from the wave equation
analysis and PDA results, it may be
necessary to restart the process, presenting
grave difficulties from a cost and
schedule standpoint, but in the author’s
experience this has never been required.
Additional notes
Unfortunately, despite the best efforts
and a carefully thought out and wellplanned
design procedure, things can
change during production driving. The
two most common problems are unanticipated
variations in subsurface conditions
and changes in the characteristics
of the pile driving system.
Piles driven short can occur due to
changes in subsurface conditions or
densification from the driving of closely
spaced piles in granular soils. If piles are
driven short, additional PDA tests can
evaluate their compression capacity, and
estimate their tension capacity. Based
on acceptable compression and tension
PDA capacities, the piles can be accepted
unless minimum tip elevations are
required for lateral support. If soil conditions
are poorer than expected, the piles
will drive longer than anticipated, posing
a problem for prestressed concrete piles
which are difficult to splice. Piles that
drive long and fail to achieve the driving
criterion can be checked by the PDA for
potential damage.
The other major problem is a change
in the energy transfer of the pile driving
system. This may result simply from wear
and tear from the continuous operation
of the hammer. Since the driving criterion
is given for a certain stroke or energy
transfer, changes during production
installation or maintenance of the hammer
should cause additional PDA testing
and a review of the criterion. Simple hammer
maintenance can change the driving
energy appreciably. On a project in Egypt
that included thousands of piles, the contractor
replaced the compression rings in
the diesel hammer during down time for
load testing and prior to production driving.
This maintenance more than doubled
the transferred energy to the pile. If not
detected by PDA, this would have caused
all piles to be significantly overdriven.
To evaluate these potential site and
hammer performance changes during
production driving for larger projects, it is
our general recommendation to PDA test
about five percent of the production piles
with tests spread out over the site and
periodically as the project progresses to
assure consistent hammer performance.
The hammer should not be replaced
simply to suit the contractor’s workload
or schedule. Even if the replacement
hammer is of the same make and model,
the driving energy can be significantly
different. PDA testing can be justified on
larger piling jobs to qualify additional
hammers and customize the driving criteria
for each hammer.
Summary and conclusions
As stated earlier, there are no new techniques
presented in this paper on how
to have a successful driven pile project.
However, benefit is gained from summarizing
the various established steps as a
single coherent process. The complete
process is applicable to large down to
moderately sized projects, particularly
where the piles are spread over a relatively
extensive area. For relatively small
projects where only a handful of piles are
needed, the process may be complete following
the PDA testing and still provide
significant benefits.
Considerable success with this process
has always resulted in successful
pile projects and no pile failures or settlements
of a structure beyond levels anticipated.
The process has been applied to
ASD Safety Factors and LRFD resistance factors
Capacity
Determination
Method
IBC
ASD
AASHTO
Before 2007
ASD
AASHTO
After 2007
LRFD
From Static Load Test and PDA Test Coupled with Wave Equation and Static
Analysis 2.0 1.9
(a)
0.80
(a)
From Static Load Test Coupled with Wave Equation and Static Analysis 2.0 2.0 0.75
From PDA Test of 100% of all piles Coupled with Wave Equation and Static Analysis 2.0 2.25
(a)
0.75
(a)
From PDA Test of at least 2 piles (minimum 2 piles) Coupled with Wave Equation
and Static Analysis 2.0 2.25
(a)
0.65
(a), (b)
From Wave Equation and Statis Analysis (c) 2.75 0.50
From Driving Formulas And/Or Static Analysis (d) 3.5 0.40
(a) Requires signal matching (CAPWAP)
(b) Some State Departments of Transportation use 0.70
(c) Only allows for design loads <40 tons, no value guidance
(d) Not allowed
Table 1
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