Volume 2, Issue 1 (March 1979)
Strength Testing of Compacted Shale
Little has been written about the strength testing of compacted soft rocks such as siltstones, claystones, mudstones, and shales. The behavior of one such Indiana shale, the New Providence, was examined. While the testing procedures generally follow those developed for compacted soils, there is sufficient individuality to suggest that a detailed description would be of interest. The preparation, shearing, and definition of failure parameters for triaxial specimens of this Indiana shale are described. A stress ratio between the compaction pressure and the preshear consolidation pressure is a kind of overconsolidation ratio and is a key to the stress-strain observations. Both highly overconsolidated and essentially normally consolidated experimental values are included. The effective stress failure parameters defined by maximum deviator stress are relatively insensitive to all testing variables for this single compacted and soaked shale, and the authors believe this to be the most appropriate failure criterion for nondurable shales.