(cm)
(in.)
0
0
AC
CL5
Frozen
50
20
CL3
Unfrozen
100
40
195960
Mean
198687
Min.
150
60
0
0
50
20
Figure 26. Frost and thaw
penetrations predicted by
100
40
FROST for freeze seasons in
197879
Max.
196465
3/30
Phase 2B environmental sen-
150
60
sitivity stud y. Simulations
0
60
120
180
240
300 0
60
120
180
240
300
start on 1 October.
Elapsed Time (days)
in the full depth sections, they were quite a bit
thaw season on the predicted performance of the
lower.
sections, an environmental effects sensitivity se-
A comparison of the Ullidtz/15K subgrade
ries was conducted using the single conventional
series results with the originally designed fail-
flexible test section, F3, which included class 5
ure at 3,300,000 applications for the 5-yr sec-
special and class 3 special materials as its base
tions and at 6,600,000 applications for the 10-
and subbase courses (Fig. 18) and a water table at
yr sections yields the following conclusions:
a depth of 2.4 m (8 ft). Prior simulations had ap-
1. In general, the Mechanistic Pavement De-
plied upper boundary temperatures from the sea-
sign Procedure predicts the 5-yr conventional sec-
son with a freezing index near to the 30-yr mean,
195960 (freezing index 1003C-days or 1806 F-
tions to fail due to asphalt cracking prior to the
end of the design life, while failure from subgrade
days). This new series applied temperatures from
rutting is predicted beyond the design life.
3 other freeze/thaw seasons, including those with
2. Predictions for the 5-yr full-depth section
freezing indices equal to the mean of the three
(F4) indicate that it will not fail from asphalt crack-
coldest seasons during the period 1959 to 1987
ing, but two of the three criteria for subgrade rut-
and the maximum and minimum for the 1959
ting indicate early failure.
1987 period. These seasons were as follows: maxi-
mum--197879 (1477 C-days or 2658 F-days),
3. The two 10-yr conventional sections with
minimum--198687 (4.67 C-days or 841 F-
class 5 and class 6 special bases (F21 and F22) are
predicted to fail from asphalt cracking at about
days), and mean 3 coldest out of 30--196465
(1391 C-days or 2503 F-days). Results from these
the end of the design applications, while subgrade
rutting criteria indicate longer life.
years were compared with f3w8 predictions for
4. The 10-yr conventional section with class 3
the mean year that had been run in the Phase 2A
special subbase (F19) may fail due to asphalt crack-
"Schmidt" series, since this Phase 2B series also
ing, but not from subgrade rutting.
used the Schmidt model for asphalt modulus cal-
5. Predictions for the 10-yr full-depth section
culations and the high density 1206 form for the
(F14) indicate that it will not fail from asphalt
subgrade modulus calculations.
cracking, but two of the three criteria for subgrade
Figure 26 shows the freeze/thaw penetration in
rutting indicate early failure.
the F3 section predicted by FROST for all four
freeze seasons. In the mean year, multiple small
freeze/thaw events were followed by a long freeze
Phase 2B
To investigate the influence of the applied freeze/
event that penetrated the subgrade and a spring
36
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