Observed Effects of Subgrade Moisture on Longitudinal Profile

This paper describes how 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, and freezing cycle, focused principally on effects of moisture in subgrade. From the statistical analysis, it was concluded that moisture in the subgrade significantly affects several wavebands, including 5.0 to 31.2 m and 5.0 to 39.0 m for freezing and non-freezing sites, respectively. In non-freezing sites, as average value and variation of moisture increase, pavement surface profile deteriorates quickly. In freezing sites, it was found that moisture variation due to frost action dominantly contributes to roughness deterioration. In addition to mean moisture and moisture variation, it was found that percent passing 0.002 mm soil size and the depth to the top of subgrade are also significant factors accelerating the roughness changes in freezing and non-freezing sites, respectively.