Extension of CBR Method to Highway Pavements

Abstract

The CBR design method for flexible airfield pavements was modified in 1971, on the basis of full‐scale tests. A new load repetition factor and Equivalent Single Wheel Load computation scheme were introduced and implemented in the modified CBR design method. In the present paper, the method is extended to flexible highway pavements. The effect of loading conditions (which are different in highway and airfield pavements), is verified using AASHO Road Test results. The load repetition factor is then adjusted for the heavy traffic range. Pavement thicknesses obtained with the extended CBR design method are compared with those obtained with the current CBR method for highways, AASHO Road Test, SHELL and the British Road Note 29. It is found that the extended CBR design method leads to: (1) A substantial reduction of pavement thickness as compared to the current CBR method; (2) a slightly thicker pavement in the light and medium traffic range and a slightly thinner pavement for heavy traffic as compared to other design methods. Design curves are presented for different subgrade CBR values.