Abstract
The California bearing ratio (CBR) procedure for the design of airfield flexible pavements was originally developed in the 1940s for supporting new heavy bombers and reviewed in the 1970s to allow handling multiwheel tire groups. In view of an active debate at the International Civil Aviation Organization level on further adjustments to the design procedure, a U.S. Army Engineer Research and Development Center (ERDC) research team reformulated the original CBR procedure. The new CBR design procedure was redefined with the introduction of Fröhlich's theory for computing the pavement thickness and validated through full-scale testing. This study evaluated the influence of each layer in the stress distribution with the final objective of recommending specific values of the Fröhlich stress concentration factor. The data for this investigation were collected during full-scale testing at the ERDC in 2008. The analysis allowed identification of several influencing factors in the stress distribution for computing the stress acting at the top of the subgrade. Such factors included the subbase and subgrade CBR, the thickness of the subbase layer, and the stress distribution represented by the respective n factor of the layer group. The linear regression confirmed the statistical importance of these variables in assessing stress distribution above the subgrade. This case study provided encouraging results for additional investigations on the stress distribution within a layered system with the objective of quantifying more accurately the stress acting at the top of the subgrade.
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