Observed evidence of subgrade moisture influence on pavement longitudinal profile

The relationship between subgrade moisture parameters and pavement profile was explored for 34 asphalt pavements of the seasonal monitoring program (SMP) in the long-term pavement performance (LTPP) program. Volumetric moisture content was quantified in terms of the moisture index (MI), representing moisture as reasonably related to subgrade performance. Using power spectral density (PSD), roughness was evaluated in 21 individual wavebands. From statistical analysis, it was concluded that subgrade moisture significantly affects roughness in the wavebands of 14.9 to 31.2 m and 24.0 to 31.2 m for nonfreezing sites, and in the waveband of 14.9 to 24.0 m for freezing sites. At nonfreezing sites, as the magnitude and variation of moisture increase, pavement surface profile deteriorates quickly. At freezing sites, it was found that moisture variation by freezing contributes to roughness deterioration. Moreover, it was found that pavement thickness and the percent passing the top 0.002 mm of subgrade are significant factors accelerating roughness progression at nonfreezing and freezing sites, respectively.