| Moisture in subgrade soils is a major environmental factor considered in pavement design. The influences of subgrade moisture on roughness of longitudinal profile were investigated for 43 asphalt pavements of the Seasonal Monitoring Program (SMP) sites in the Long-Term Pavement Performance (LTPP) program. Volumetric moisture content in the subgrade was quantified as a moisture index, computing means and standard deviations for that moisture index during seasonal monitoring periods. Using the power spectral density function, roughness of a longitudinal profile was evaluated using the root mean square values in all possible ranges of wavebands. Then, the time-dependent change of the roughness values in each waveband was statistically analyzed with soil information, freezing index, freezing cycle, freezing depth, heave rate, and measurement year, focused principally on effects of moisture in subgrade. From the statistical analysis, it was concluded that moisture in the subgrade significantly affects longitudinal profile roughness in several wavebands. It was found that dominant wavebands responding to the moisture are 14.9 to 31.2 m and 24.0 to 31.2 m for non-freezing sites, and 14.9 to 24.0 m for freezing sites. Those, wavebands are coincident with the wavebands that affect ride quality and driving safety. In non-freezing sites, as mean and standard deviation of moisture increase, pavement surface profile deteriorates quickly. In freezing sites, it was found that normalized moisture variation due to frost action dominantly contributes to roughness deterioration. In addition to mean moisture and moisture variation, it was found that the depth to the top of subgrade and percent passing 0.002 mm soil size are also significant factors accelerating the roughness changes in non-freezing and freezing sites, respectively.; For practical application of these results, their influence on International Roughness Index (IRI) value was examined, considering the wavebands affected by subgrade moisture. |
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