Development and validation of a stress-based procedure for the design of military flexible pavements.

摘要

This research study focuses on the development, validation and implementation of a new stress-based design procedure for military flexible airfield pavements. This proposed new procedure is based on the U.S. Army Corps of Engineers California Bearing Ratio (CBR) design methodology. The CBR design methodology has its roots on a very simple, but still reasonable theoretical approach, where the pavement is modeled by a single layer system described by the Boussinesq half-space stress model.;The objective to develop a new stress-based design procedure was fostered by the results of an extensive literature review on the early work done during the development of the original CBR procedure. This literature review revealed that the CBR procedure was fundamentally derived from sound theoretical basis and was actually developed as a stress-based methodology that followed a soil stress model proposed by O. K. Frohlich in 1934. It was found that Frohlich's stress equations for vertical stress, which make use of a stress concentration factor to improve predictions of stresses within a soil mass, can be used to derive the current form of the fundamental equation in which the CBR procedure is based on.;The discovery that the original CBR procedure pointed to a stress-based design approach led to the further investigation of the mathematical basis of the original CBR equation. This research focused its effort in the re-formulation of the basic CBR equation, corroborating its validity and developing a complete system for the design of flexible pavements using a stress-based approach. To develop, validate and implement the proposed stress-based design procedure, this research study was undertaken to fulfill the following objectives.;The first objective was to review and consolidate all historical information on the origins of the classical CBR equation and to reformulate its mathematical derivation into a stress-based approach. The second objective was to introduce a new stress-based criterion, called the CBR-Beta procedure, for design of flexible pavements. The third objective consisted of performing experiments to help validate the stress distribution within pavement structures subjected to various aircraft loadings. A full-scale experiment was developed to construct twelve flexible pavement test sections so that the proposed CBR-Beta procedure could be implemented and studied in the field. The fourth objective was to further validate the proposed stress-based CBR design procedure utilizing the results of field traffic experiments, laboratory testing and modeling. Finally, the fifth objective was to consolidate all the results from full-scale traffic testing, validation of stress distribution within a pavement structure and modeling into a cohesive and complete stress-based design procedure.;The results of this PhD study have demonstrated that the new re-formulation of the CBR procedure can be applied to the structural thickness designs of flexible pavements. The new form of the CBR-Beta criterion was found to be of mechanistic nature and was validated by traffic tests. The new CBR-Beta design procedure compared favorably against the existing CBR and layered elastic procedures. The CBR-Beta procedure improved on the existing CBR procedure by: (i) making the performance criteria more visible in terms of vertical stress versus passes to failure, (ii) directly considering multi-wheel gear assemblies without resorting to gear equivalencies, and (iii) eliminating the need for thickness correction factors. All these new aspects of the CBR-Beta procedure were incorporated into a complete system and recommended for implementation as the standard for the design and evaluation of military airfield pavements.