Development of a mechanistic-empirical model to predict equilibrium suction for subgrade soil

Suction in subgrade layer reaches an equilibrium condition several years after construction of the pavement. The equilibrium suction has a direct influence on the resilient modulus of subgrade soil. In the current mechanistic-empirical pavement design guide, equilibrium suction is determined based on the empirical relationship with water table depth. However studies have shown that other critical factors also influence equilibrium suction. In this study, a new mechanistic-empirical model is presented to predict equilibrium suction considering the effects of physical properties of the soil and climatic factors. A simple regression model is also generated to predict the equilibrium suction from readily available parameters i.e., Thornthwaite moisture index (TMI), plasticity index (PI), and dry suction value at surface (u_dry). In the final section of this paper, the effects of TMI and vegetation on equilibrium suction are evaluated for various soil classes and TMI ranges, respectively. A contour map of the equilibrium suction values for the entire continental United States has been generated using the geographic information system (GIS) platform and followed by the model predictions.