Incorporation of the soil-water characteristic curve hysteresis in pavement design

The Mechanistic Empirical Pavement Design Guide (MEPDG) incorporates unsaturated soil mechanics into the analysis and pavement design. This task is accomplished by using climatic and soil properties to estimate the suction, which along with the Soil-Water Characteristic Curve (SWCC) are used to determine the degree of saturation. Although large strives have been made to incorporate unsaturated soil mechanics in pavement design, the MEPDG does not incorporate the hysteretic behavior of the SWCC but rather, the analysis is performed using only the drying branch. This paper presents a stochastic evaluation of the models used in the MEPDG to estimate the water content of the unbound/ granular materials considering the hysteretic behavior of the SWCC. It was found that the prediction of the resilient modulus is overly conservative for any climatic condition when hysteresis is not considered and therefore, consideration of the SWCC hysteresis in pavement design and analysis is necessary and recommended.