EI 02C097
01 Jul 97
velocity determined by integration of the acceleration. The
provided to the contractor to optimize selection of driving
CAPWAPC method calculates the force required to give the
equipment and cushions, to optimize pile driving, to reduce pile
imposed velocity. This calculated force is compared with the
stresses, to reduce construction cost, and to improve construction
force measured at the pile top. The soil input parameters are
quality. The foundation will be of higher quality, and structural
subsequently adjusted until the calculated and measured forces
integrity is more thoroughly confirmed with the PDA method
and calculated and measured velocities agree as closely as
because more piles can be tested by restriking the pile than can
practical such as illustrated in Figure 6-3. The CAPWAPC
be tested by applying actual static loads. PDA can also be used
method may also be started by using a force imposed at the pile
to simulate pile load test to failure, but the pile can still be used
top rather than an imposed velocity. The velocity is calculated
as part of the foundation, while actual piles loaded to failure may
and then compared with the velocity measured at the pile top.
not be suitable foundation elements.
The CAPWAPC method is applicable for simulating static and
3. Drilled Shafts
dynamic tests.
(b) A simulated static load test may be performed using the
Drilled shafts should be constructed adequately and certified by
pile and soil models determined from results of a CAPWAPC
the inspector. Large shafts supporting major structures are
analysis. The pile is incrementally loaded, and the force and
sometimes tested to ensure compliance with plans and
displacements at the top of the pile are computed to determine
specifications. Sonic techniques may be used to ascertain
the load-displacement behavior. Actual static load test results
homogeneity of the foundation. Sonic wave propagation with
can be simulated within 10 to 15 percent of computed results if
receiver embedded in the concrete is the most reliable method
the available static resistance is fully mobilized and time
for detecting voids or other defects. Striking a drilled shaft as ina
dependent soil strength changes such as soil freeze or relaxation
large strain test with PDA and wave equation analysis is
are negligible.
recommended for analysis of the ultimate pile capacity and load-
displacement behavior as decribed above for driven piles. A
(c) Dynamic tests with PDA and the CAPWAPC method
large strain test may be conducted by dropping a heavy load onto
provide detailed information that can be used with load factor
the head of the shaft using a crane. Static load tests are
design and statistical procedures to reduce factors of safety and
commonly performed on selected shafts or test shafts of large
reduce foundation cost. The detailed information on hammer
construction projects to verify shaft performance and efficiency
performance, driving system, and the pile material can be
of the design.
6-7
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