Figure 8.10 and Table 8.1 show the weakening of a road structure after spring thaw. The stiffness modulus E2 of the whole pavement structure measured by the FWD is, on average, 13% lower in the spring time than it is before the next freezing period. According to the FWD indices, the reason is the weakening of the upper structure. This is shown since the BCI-indices (which are a representation of deflection in the subsoil) remain about the same, but the upper structure is weakened: the SCI (which is a representation of near-surface deflections) rises by 22%. The reason for this is that there must be more moisture in the structure after the thawing than in late autumn. The temperature of the pavement has been taken into account in the calculation on the indices. The data is from a 5.5 km long old highway section of highway #6 in Finland with an AADT of 6500, before rehabilitation measures.
Figure 8.11 shows an example of a poor quality aggregate base layer in the middle of the above section. In the central length of the road the SCI is very high, indicating that there are a lot of fines in the base layer.
E2 (MN/m2),
SCI300, BCI (pm)
800
700 300
200
E2 (MN/m2),
SCI300, BCI (pm)
800
700
600
500
400
300
200
100
0
5000 5200 5400 5600 5800 6000 6200 6400 6600 6800 7000 7200
Distance (m)
