Premature failure of flexible pavements has long been a problem in many Egyptians roads with the drastic increase in truck axle loads. To fully utilize each pavement material in an economic design, a pavement should generally have reasonably balanced design between the rutting and fatigue modes of distress. The purpose of this paper is to develop a methodology for achieving a reasonable balance between fatigue and rutting lives of flexible pavements. The methodology is based on the damage analysis concept which is performed for both fatigue cracking and rutting on different pavement sections using KENLAYER program. The investigated pavement components are; thickness (d1 and d2) and elasticity modulus (E1 and E2) for asphalt layer and base layer, respectively, and subgrade elasticity modulus (E3).
The results of pavement analysis showed that d2 and E3 are the key elements which control the equilibrium between fatigue and rutting lives (Nr, and Nr, respectively). That is because, increasing d2 and E3 sharply increases Ng, and don't affect in Nr. The study also concluded that, increasing dl significantly increases both Nf and Nr, while increasing E2 and El mildly increases Nf and Nr. Finally, the study has recommended pavement sections with any values of d1, El or E2 at d2 = 12-in. along with E3 = 8,000 psi, for optimum utilization of pavement components with respect to fatigue and rutting.