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77
Figure 74 shows the regression curve for the J
c
.
This curve is significant,
because it allows us to obtain a Case damping coefficient, J
c
, directly from the PDA
traces, without taking into consideration the soil type in which the pile is embedded.
The
suggested equation to correlate tip to skin ratio to J
c
is
2686
.
0
ln
09744
.
0
+

=
Skin
Tip
J
c
(76)
Because the latter equation was obtained from a comparison with the Davisson’s
capacity at BOR, it is only recommended for estimating the pile capacity from dynamic
tests performed at BOR.
Sensitivity Analysis of Case Damping Coefficient, J
c
In order to measure how sensitive the Case method resistance (RSP) solution is to
the variation of J
c
, the coefficient of variance was used.
The following steps were
followed to obtain a relation between the coefficient of variance for the resistance and the
coefficient of variance for J
c
.
Using the Case method solution for the pile resistance, R,
the average (bars for average) resistance based on the average value of J
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 Spring '11
 Hass

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