Development of a new durability index for compacted shale

Many highway embankments in the East Central United States and around the world have been constructed using compacted shale. When weathered, shale tends to degrade into a fine-grained mass of soil with high compressibility and low shear strength. Unfortunately, there are no reliable methods to predict the long-term behavior of compacted shale subjected to deterioration resulting from the weathering process. This study presents the results of analyses for index and geotechnical laboratory tests on both weathered and unweathered shale samples, durability tests on unweathered samples, and compaction and triaxial shear tests on compacted weathered shale samples. The result of this effort is the development of a new durability index that better characterizes the durability behavior of shales than the standard slake durability index. This new index is simple to perform and is well correlated with index and geotechnical properties of unweathered and weathered shale. A secondary result of this study is the development of a simple and reliable means to evaluate the shear strength of compacted shale behavior and swelling of core samples as a function of durability. ► Index tests were performed on compacted weathered and unweathered shale samples. ► A new durability index developed from a series of modified slake durability tests. ► The new durability index is well correlated with properties of weathered shale. ► The new index provides a means to evaluate engineering behavior of compacted shale.