Mechanistic-Empirical Procedure for Flexible Airfield Pavement Design: The New French Technical Guidance

Abstract

Empirical procedures based on the California bearing ratio (CBR) method for the design of flexible airfield pavements have shown many limitations in the past decades. Much effort has been made to overcome them, leading to the development of new methodologies associated with new computer programs (APSDS, FAARFIELD, PAVERS…). The French Civil Aviation Technical Center released its new pavement design guide Rational Design Method for Flexible Airfield Pavements (STAC, 2014) describing the complete procedure based on rational principles. A dedicated software, Alize-Airfield Pavement, was developed for its implementation. This French procedure is based on the computation of resilient stresses and strains in the pavement structure using a multi-layer linear elastic model. Two failure criteria are taken into account: permanent deformations of the subgrade, and fatigue of asphalt mixtures. Damages induced by each aircraft of the traffic mix are cumulated over the design period. The failure models used are derived from laboratory testing on pavement materials, observation of in-service airfield pavements, as well as experimental programs carried out in the early 2000s in Toulouse-Blagnac airport with a full-scale heavy simulator. This procedure fulfills many of the ambitions that were raised by the limitations of the former empirical method. For instance, it is now adapted to any type of landing gear including the most complex configurations. The most advanced developments that are implemented allow describing in a complete manner some effects such as successive loadings induced by 6 or 4-wheel landing gear, or lateral wander of aircraft, which makes it an optimizing tool. This paper describes the content of the design guide and its field of application, including a design example with the Alize-Airfield Pavement software. The method has now become the recommendation of the French Civil Aviation Authority.