OVERLAY THICKNESS DESIGN FOR FLEXIBLE PAVEMENT

An overlay design method for flexible pavement is presented in which both functional and structural types of performance are considered. The method relates the overlay thickness to various types of failure of the overlaid pavement, such as fatigue and lowtemperature cracking, rutting, and roughness. The viscoelastic, plastic, and fatigue properties of the pavement materials are considered. The computer program OVERLAY is developed by modifying the FHWA program VESYS-3-A in order to determine the optimum overlay thickness. The method provides a probabilistic solution and allows for the use of different material properties for different seasons. The use of the method is verified by determining the required overlay thicknesses for two typical pavement conditions under typical traffic volumes, material properties, and environmental conditions. The use of the method is justified in view of the rising cost of pavement rehabilitation.