Significance of Unsaturated Analysis in Performance Evaluation of Pavement Drainage Systems

Design and analysis of drainage systems in flexible pavements require proper understanding of the pavement's response to the ingress of water. For the sake of simplicity, investigation of adequacy of drainage systems in flexible pavements is usually carried out assuming saturated state for the foundation layers. However, several studies have confirmed that the water regime within pavement layers is controlled by unsaturated flow principles. This paper demonstrates the significance of unsaturated analysis of pavement drainage through a comparison of results from DRIP and VS2DI a finite difference software package, which consider saturated and unsaturated analyses, respectively. A typical pavement structure with edge-drain was modeled using DRIP and VS2DI. The results of sensitivity analyses indicated that DRIP may be unconservative since it generally underestimates the time-to-drain compared to the unsaturated analysis. The findings of this research suggest that using a more refined analysis tool for the design of drainage systems in pavements may be desirable.