CUMDAM program was also remedied--
correcting the value of the subgrade modu-
lus used in the Corps of Engineers vertical
strain damage calculation. Table 17 lists the
results of this series in the rows labeled
"Schmidt." In general, predictions of appli-
cations to failure in the conventional cross
sections were less than in the original series
using the horizontal strain criteria and greater
using the vertical strain criteria. In the full
depth sections (F4 and F14), applications to
failure were increased in both the horizontal
and vertical strain criteria.
The second series addressed the issue that
the Phase 1 simulations computed summer
asphalt moduli that were lower than consid-
ered reasonable. In this series, the Ullidtz
model was used to calculate the asphalt
modulus at temperatures greater 1C; at cold-
er temperatures, the Schmidt model was used
(Fig. 7). This series also used the high den-
sity 1206 form for the subgrade modulus
calculations. Results for this series are shown
in Table 17 in rows labeled "Ullidtz." In
nearly all cases, this series produced higher
predicted applications to failure than the cor-
responding Schmidt series.
The third series also used the Ullidtz model
to calculate the asphalt modulus. In addi-
tion, it addressed the problem from the Phase
Figure 25. Cumulative damage for case r5w6.
1 simulations that during the summer the
predicted subgrade moduli based on the
Phase 2A
high-density 1206, or "normal" form were higher
To address problems discovered in the Phase 1
than FWD-measured values. For this series, the
modeling series, three additional simulation se-
unfrozen subgrade modulus, when recovered, was
set to be constant at 1.03 105 kPa (15,000 lb/
ries were conducted on the eight flexible test sec-
tions studied in Phase 1 with the water table lo-
in.2). This value was chosen as being approxi-
cated at the shallowest position. A change that
mately equal to an average value back-calculated
applied to all three series was that the normalized
from FWD measurements on subgrade during fall
volumetric unfrozen water content form of the
1991.* As a result of this modulus approxima-
frozen modulus equations (Table 1a), rather than
tion, the linear model (model 0 in Table 2) was
the normalized gravimetric form used in Phase 1.
used in NELAPAV for all subgrade calculations.
The first of the new series was essentially a
The applications to failure from this series are
repeat of the initial series in that it used the Schmidt
listed in Table 17 as "Ull-15K." In the conven-
model (Fig. 7) for calculation of the asphalt modu-
tional sections including a base/subbase, the ap-
lus and the high density 1206 form of the subgrade
plications to failure were slightly lower than those
for modulus calculations. It differed from the in-
resulting from the previous case with the Ullidtz
itial series in that the normalized volumetric
asphalt model and the higher-modulus subgrade;
unfrozen water content form of the frozen mod-
ulus equations was utilized. A mistake in the
* D. Van Deusen, Mn/ROAD, person. comm. 1992.
34
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