The design of pavements requires a knowledge of the relative strength and durability of subgrade materials. In Kentucky, the CBR (California Bearing Ratio) test is used to define the relative bearing strength of subgrade materials. Pavement thickness can be obtained if traffic loadings and CBR values are known. Durability of subgrade materials can be characterized using the slake-durability test. The purposes of this study were to correlate values of (soaked) KYCBR and slake-durability indices and examine the swell potential of compacted shales. Correlations were developed between soaked KYCBRs and slake-durability indices obtained from three different slake-durability I testing procedures. The first correlation used slake-durability indices from a testing procedure devised and proposed initially by Franklin and Chandra and modified by Gamble. The second and third correlations use slake-durability indices obtained from testing procedures proposed by Hopkins and Gilpin. Correlations of soaked KYCBRs and in situ water contents of unweathered shale and clay contents of shales are also presented. Based on these correlations, estimates of soaked values of KYCBRs of shales can be obtained. Consequently, the desirability or suitability of certain types of shales for use in pavement subgrades can be quickly estimated.

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The contents of this report reflect the views of the author who is responsible for the facts and the accuracy of the data presented herein. The contents do not necessarily reflect the official views or policies of the Kentucky Transportation Cabinet, the Federal Highway Administration, nor of the University of Kentucky. This report does not constitute a standard, specification, or regulation.