PILE DRIVING PROCESS
pile hammer efficiency is also usually less
than that originally assumed. Once the
pile hammer efficiency adjustment is
made and the CAPWAP soil model is used
in a refined wave equation analysis, close
agreement generally can be achieved.
Capacity results from the retap testing
give the best correlation with the longterm
service condition. Upon completion
of the review of all available data, adjusted
driving criteria can be determined.
For relatively small projects, this may be
the end of the process and all production
piles are then driven to the criterion
established by the probe pile testing.
For larger projects, a probe pile may be
selected for a static load test, or a special
pile may be installed to the revised driving
criterion and designated for a static
load test.
Drive test piles for static load testing.
Many will argue that using static
load testing in addition to running PDA is
overkill. For larger piling projects, static
load testing is justified in addition to PDA
testing. (On many projects some static
load tests can be replaced by additional
PDA tests). The test piles are driven at
various locations of differing soil conditions
using the adjusted driving criteria.
The test pile driving is monitored using
PDA to confirm the pile driving hammer
performance, and the predicted capacity
from a retap will be compared to the pile
capacity that will be measured from the
static load test.
Static load testing. The static axial
compressive load testing on each project
is performed according to ASTM D 1143
using either the maintained or usually the
quick load test procedure. The load testing
should be conducted to three times
the allowable design loading or to failure,
whichever occurs first. Once the load
testing is completed, the load test curve
is evaluated to determine the ultimate
pile capacity. The Davisson method is
most often used to estimate the ultimate
pile capacity. The allowable capacity is
then determined by applying a safety factor
to this ultimate capacity. Table 1 presents
safety factors for allowable stress
design (ASD) from the International
Building Code (IBC) for private works
in the USA and AASHTO resistance factors
for LRFD designs now used in USA
highway work. The most economical
factors (lowest safety factors or highest
Continued on page 96
Many will argue that
using static load
testing in addition
to running PDA is
overkill. For larger
piling projects,
static load testing is
justified in addition
to PDA testing.
94 | ISSUE 4 2020 www.piledrivers.org
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