only during spring thaw in the 198586 season, and
parently, a more sophisticated index that perhaps
the corresponding total damage accumulation was
combines freeze index, severity of midwinter thaw
much less.
events, and other parameters is required to corre-
Based on the above observation, we tried a new
late with predicted damage.
approach to quantifying the characteristics of the
In analyzing the Phase 3 simulation results, we
freeze seasons. It involved summing the thawing
examined the distribution of predicted damage
degree days experienced during the freeze season
through the four seasons defined as follows: fall--
in two ways. The first was a total from all events,
1 October to start of freeze, winter--freeze sea-
and the second was a total from only the thaw
son as defined by freezing index, spring--75 days
events that exceeded 16C-days (30F-days) (Table
following end of freeze season, summer--remain-
18). The quantity 16C-days was chosen based on
der of 365-day simulation. The simulations pre-
analysis by Mahoney et al. (1985) indicating that
dicted a wide variation in seasonal damage
pavements approach their critically weak condi-
amounts for different years, especially in the ver-
tion after this amount of thaw has been experi-
tical strain damage in the conventional cross sec-
enced. Unfortunately, neither of these quantities
tion (Fig. 20). In years when vertical strain dam-
correlated with predicted damage amounts. Ap-
age was predicted for the conventional cross
0.03
0.6
Fall
Winter
Spring
Summer
Fall
Winter
Spring
Summer
0.4
0.02
0.2
0.01
0
0
1970
1975
1980
1985
1990
1970
1975
1980
1985
1990
a. Conventional section, Asphalt Institute horizontal
c. Full depth section, Asphalt Institute horizontal strain
strain model MS-11.
model MS-11.
0.04
0.6
Fall
Winter
Spring
Summer
Fall
Winter
Spring
Summer
0.03
0.4
0.02
0.2
0.01
0
0
1970
1975
1980
1985
1990
1970
1975
1980
1985
1990
b. Conventional section, Asphalt Institute vertical strain
d. Full depth section, Asphalt Institute vertical strain
model MS-1.
model MS-1.
Figure 20. Distribution of cumulative damage during seasons.
32
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