Reliability Design Procedures for Flexible Pavements

A procedure is developed to analyze layered elastic flexible pavement systems in terms of reliability. Rosenblueth's method is used to estimate the expected value and variance of the strains (dependent parameters), based on the input mean values of independent parameters, i.e., aircraft load, layer thicknesses, and material moduli. Relationships between reliability level and allowable strain repetition of the designed system provide a decision‐making tool for engineers to design pavements at a desired reliability level. The design can be optimized by selecting thicknesses of bituminous concrete and base layers so that the pavement fails in fatigue cracking of the bituminous concrete and subgrade at nearly the same traffic level for a given reliability level. The performance of conventional flexible pavement is sensitive, in descending order, to variations of gear load P, thickness of the granular base $h_2\text{,}$ subgrade modulus $E_3\text{,}$ and thickness and modulus of the bituminous‐concrete surface course $h_1$ and $E_1\text{,}$ respectively, for the subgrade strain‐failure criterion, and to variations of P, $h_1\text{,}$ $E_1\text{,}$ $E_2\text{,}$ $h_2\text{,}$ and $E_3$ for the bituminousconcrete strain‐failure criteria.