Hydraulic design of granular and geocomposite drainage layers in pavements based on demand-capacity modeling

Abstract

In this paper, a new approach based on the demand-capacity model is developed for hydraulic design of granular and granular-cum-geocomposite drainage layers in pavements. The demand is given by the intensity-duration curve obtained from the Intensity-Duration-Frequency curve, which is geographic location specific and corrected for climate change. The capacity curve corresponds to critical infiltration rates and critical durations for a drainage layer which is influenced by the hydraulic and geometric characteristics. The design is acceptable if the capacity curve exceeds the demand curve. The design framework is illustrated for typical geometries of highway pavements with three granular gradations and three geocomposites. Based on the developed framework, hydraulic equivalence is defined and evaluated for the drainage layers. The permissible reduction of granular layer thickness for hydraulic equivalence is evaluated if geocomposite is embedded in the subbase layer of pavements. For an optimum gradation based on hydraulic and structural characteristics, the thickness of granular layer with geocomposite could be reduced by 30% compared to the granular layer without geocomposite, which showed similar hydraulic performance. The significance of drainage layer thickness with geocomposite is shown based on the demand for storage to satisfy the drainage requirement for rainfall events of high intensities and long durations.