Methodology to evaluate performance of pavement structure using soil moisture profile

Variation of moisture content in the subgrade layer of a flexible pavement may play a significant role in its structural performance by influencing the stiffness of the pavement system. The objective of this study is to develop and test methodologies to incorporate the soil moisture profile into flexible pavement evaluation and to determine how the changes of water table level will affect the pavement deformation. Falling weight deflectometer (FWD) data at two locations in Minnesota and Oklahoma were used to estimate the in situ measured pavement deformation with seasonal changes of water content. Then, a layer elastic analysis approach was adjusted to include the moisture dependency of the subgrade resilient modulus in calculating the deflection basin. The controlling parameters in these set of analyses were asphalt layer temperature, the degree of water saturation in unbound materials, depth to the groundwater table, and depth to bedrock. The environmental data for this study were obtained from the Long Term Pavement Performance-Seasonal Monitoring Program (LTPP-SMP) for the two pavement sections for different climatic conditions. The comparisons showed that dividing the subgrade layer into sublayers with variable, moisture-dependent modulus according to the location of moisture measurements will result in more accurate estimation of the pavement deflection. In addition, the predicted deflections indicated that considering moisture data up to the depth associated with 10% of surface vertical stress may suffice for this type of analysis. However, the overall quality of prediction is sensitive to the material type in the subgrade layer.