Results obtained from a series of engineering tests performed on 40 different types of shales are summarized and discussed. Both hard and soft shales, as well as shales having well-documented histories of involvement in highway embankment failures and shales having little known involvement, were tested. A major portion of the report examines the suitability of the slake-durability tests, originally devised by Franklin-Chandra of England, as a means of broadly characterizing the engineering properties of Kentucky shales. Results obtained from ten different slake-durability testing procedures, which include procedures proposed by Franklin and Chandra and others as well as procedures devised during the study, were compared. Two procedures devised during the study appear to better characterize slake-durability properties of shales than procedures previously proposed. Natural water contents and jar slake tests were performed to determine if such tests might provide a fairly rapid means of identifying troublesome shales. The natural water content of a shale is a strong indicator of the slake-durability properties. Comprehensive mineral analyses were performed. Only a slight relationship between engineering performance and mineral composition was found. Most notably, montmorillonite was not present in any of the selected shales. Swelling properties of ten shale types were examined. A good correlation was obtained between a newly devised slake-durability index and the water content of a shale after swelling was completed. When exposed to water, most of the shales exhibited high swell pressures. Particle-size determinations, specific gravity tests, and Atterberg limits were performed. Correlations obtained from these tests and slake durability indices are described. Hardness characteristics of the shales were studied using the Shore scleroscope.

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The contents of this report reflect the views of the authors who are 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 Department of Transportation, of the Federal Highway Administration nor of the University of Kentucky. This report does not constitute a standard, specification, or regulation.