PCC, E 1, ν = 0.15
PCC, E 1, ν = 0.15
h1
h1
h2
h2
Base, E 2 ν = 0.35
Base, E 2, ν = 0.35
,
6.1 m
Subgrade, E 3, ν = 0.40
Subgrade, E 3, ν = 0.40
h3
h3
Bedrock
Rigid Layer
a. OCA.
b. CWA.
Figure 14. Idealized pavement structures.
40
E = 27,580 MPa
E = 34,475 MPa
E = 41,370 MPa
30
20
10
Outagamie County Airport
0
14 Mar
19
24
29
3 Apr
8
13
18
23
28
Figure 15. Effect of PCC Modulus on WESDEF absolute error (OCA).
calculated the deflections (Fig. 15). The Absolute
17/35) and attempted to backcalculate the layer modu-
Arithmetic (AA) error is the absolute sum of the errors
lus during the thaw period. While at OCA bedrock
between measured and calculated deflections for the
was at least 4 m deep, at CWA bedrock was close to
seven sensors.
the surface at some of the FWD locations. The sites
2. Changing the PCC modulus within the range did
selected represented bedrock at various depths. Thick-
not significantly affect the subgrade modulus (Fig. 16).
nesses of the subgrade layers are shown in Table 5. We
We also found that the subgrade modulus obtained
Table 5. Thickness of subgrade at back-
from the first attempt, i.e., when the modulus of the
calculated FWD locations.
PCC layer was not established at some particular val-
ue, was very similar to that obtained when it was. This
Subgrade
Subgrade
FWD
thickness
FWD
thickness
infers that, as far as the subgrade modulus is con-
location
(mm)
location
(mm)
cerned, large differences between the measured and
calculated deflections can be tolerated for PCC pave-
2
2435
16
1829
ment.
6
1092
17
3785
9
5613
18
3073
Changing the PCC modulus generally had a signifi-
15
610
19
2743
cant effect on the base course modulus. Results gener-
ated by increasing the PCC modulus showed a de-
crease in the backcalculated base course modulus.
also attempted to backcalculate the base course modu-
However, in general at OCA, the backcalculated mod-
lus under FWD location 3. Location 3 was different
uli were quite low, as shown in Figure 17. With the
from the other sites because the base course layer was
exception of a few locations, the results were too errat-
founded directly on top of the bedrock. The structure
ic to make any meaningful conclusions.
at FWD location 3 was 330 mm of PCC over 1220
At CWA, we selected a number of sites (FWD sites
mm of base over bedrock. We were unable to get rea-
2, 6 and 9 on runway 8/26 and 15 to 19 on runway
sonable agreement between the calculated and mea-
15
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