Evaluation of Pavement Subgrade Long-term Equilibrium Moisture with Suction Potential

The objective of this study was to find the relationship between soil suction potential and moisture change from the Optimum Moisture Content (OMC) to the long-term equilibrium moisture. The sixty-five Seasonal Monitoring Program (SMP) sites in the Long Term Pavement Performance (LTPP) program were employed. Suction potential was evaluated using the Soil Water Characteristic Curve (SWCC) characterized. Moisture change wetting and drying from OMC was identified. Maximum wetting moistures are 15.3 and 19.9 percent from OMC and maximum drying moistures are -10.3 and -15.4 percent from OMC for flexible and rigid pavements, respectively. Once reaching equilibrium, the moisture variations were mostly less than 1 percent in terms of gravimetric moisture. OMC has a significant correlation to the percentage passing at 0.02 mm sieve size. As suction potential increased, subgrade became more wetted. The characteristic was more noticeable in rigid than flexible pavements. Groundwater table and precipitation were found not to be dominant factors in causing long-term moisture changes.