Correlation between durability and geotechnical properties of compacted shales

In many areas of the United States, shale is used in the construction of highway embankments and pavement subgrades due to the lack of economical alternate materials. Immediately after construction, compacted shale exhibits an acceptable range of engineering properties and behaviors. Unfortunately, with time and in the presence of wet conditions, compacted shale becomes less durable. This reduction in durability translates to the reduction of stability and loss of bearing capacity. This paper presents the results and analysis of several engineering tests performed on a number of different unweathered and weathered shale samples in Kentucky. Slake-durability tests were performed on unweathered shale samples while consolidated undrained triaxial compression tests were performed on compacted weathered shale samples. The test data suggest that the clay fraction of crushed unweathered samples correlates with the consistency index. Also, the ratio between the slake-durability index and clay fraction correlates with natural water content. Finally, this durability ratio can be used to predict the effective critical state friction angle of compacted shale. In general, correlations between the durability ratio and geotechnical properties provided a means to estimate the suitability of compacted shale typically used in embankments and pavement subgrades.