Difference between Pavement Thickness Design and Pavement Life Prediction for Rigid Aircraft Pavements

Aircraft pavements are generally designed using deterministic methods and using conservatively selected input parameter values, which combine to result in a low probability of structural failure occurring during the structural design life of the pavement. In contrast, when predicting the actual time until an as-constructed pavement will reach a structural failure condition, stochastic methods are required to take into account the inherently variable nature of pavement material properties and layer thicknesses, and the best-estimate of the input parameter values must replace the conservative values that are commonly used to introduce design reliability. A case study on a rigid aircraft pavement demonstrates the difference between pavement thickness design and pavement life prediction. Using Monte Carlo simulation, it was found that 98.5% of the as-constructed pavement was stronger than the designed pavement and that the predicted fatigue life of the pavement was approximately 180 times greater than the effective design life. It was concluded that the significant difference between pavement design and pavement life prediction explains the practical observation that rigid aircraft pavement service life generally exceeds typical structural design lives.