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