EI 02C097
01 Jul 97
t1 is often selected as the time at the first maximum velocity. R is
the sum of the static soil (displacement dependent), Qu and the
dynamic (velocity dependent) D components are of the capacity.
(b) Static soil capacity Qu can be calculated from R by
(6-2)
Qu ' R & Jc ( 2 Zp Vtop & R)
where Vtop is the velocity of the wave measured at the pile top at
time t1. Approximate damping constants Jc have already been
determined for soils as given in Table 6-2 by comparing Case
method calculations of static capacity with results of load tests.
J c can be fine tuned to actual soil conditions if load test results
are available.
(c) Proper calculation of Qu requires that the displacement
the quake (soil compression) required for full mobilization of
soil r esistance. Selection of time t1 corresponding to the first
maximum velocity is usually sufficient.
(d) A correction for ealy skin friction unloading causing a
negative velocity may be required for long piles with high skin
friction. The upper shaft friction may unload if the pile top is
moving upward before the full resistance is mobilized. A proper
correction can be made by adding the skin friction resistance that
was unloaded to the mobilized soil resistance.
(e) Proper calculation to static resistance requires that freeze
or relaxation effects are not present. Piles may be restruck after
a waiting period such as 1 day or more to allow dissipation of
pore water pressures.
(f) The driving force must be sufficient to cause the soil to
fail; otherwise, ultimate capacity is only partially mobilized and
the full soil resistance will not be measured.
(3) CAPWAPC method. This is an analytical method that
combines field measured data with wave equation analysis to
calculate the static ultimate bearing capacity and distribution of
pile load-displacement behavior calculated by the CAPWAPC
method may be used to evaluate the damping constant Jc ,
quakes and soil resistances required in the Case method, and to
confirm the determination of Qu calculated using the Case
method. The CAPWAPC method is often used as a supplement
to load tests and may replace some load tests.
(a) The CAPWAPC method is begun using a complete set
of assumed input parameters to perform a wave equation
analysis. The hammer model, which is used to calculate the pile
velocity at the top, is replaced by a velocity that is imposed at the
top pile element. The imposed velocity is made equal to the
6-6
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