Shear Strength of Compacted Shales

Some basic physical and engineering properties of a broad range of different types of shales located in Kentucky are examined. Physical testing included liquid limit, plastic limit, specific gravity, particle-size analysis, natural water content, and jar-slake determinations. These tests were performed on some forty different types of shales selected from various geological formations of different periods. Geological periods included Recent, Cretaceous, Tertiary, Pennsylvanian Mississippian, Silurian, Ordovician, and Devonian. Engineering tests included slake-durability, bearing ratio, consolidated-undrained triaxial compression tests with pore-pressue measurements, moisture-density relationships, well deflection and pressure, mineralogy, and Shore sclorescope. Ten different slake-durability testing procedures, including the original procedure proposed by Franklin and Chandra, are examined in detail. A new slake-durability testing procedure and the procedure proposed by Franklin and Chandra are examined in detail. A new slake-durability, testing procedure is recommended, although the standard (a modified form suggested by Gamble) procedure was found to be satisfactory for identifying important properties of Kentucky shales. Bearing ratios were determined on soaked and unsoaked compacted specimens of fourteen different types of shales. Nine types of shales were selected for triaxial tests. The triaxial tests were performed on specimens remolded to conform to standard, modified, and low-energy compaction. Values of φʹ and ϛʹ defined by the peak values of (σʹ1 — σʹ3) were usually lower and high, respectively, than values defined by the peak values of (σʹ1 / σʹ3). Frequently, it is not clear which set of φʹ and ϛʹ values should be used when analyzing the stability of compacted shale embankment slopes. It is recommended that both sets of parameters be used in stability analyses to determine which is the most conservative. The natural water content of an unweathered shale was a good predictor important engineering properties. This simple inexpensive test was correlated with bearing ratio (CBR), clay content, and the effective stress parameter φʹ. Correlations were developed between the ration H10 of the slake-durability index and the percent finer than the 0.002 mm and φʹ. Also, H10 is correlated with bearing ratio. A method is presented for predicting the effective street parameter ϛʹ using the molding water content and the parameter H10. Preliminary results from three shale test embankments compacted according to a special provision are presented. The intermediate and soil-like shales of the embankments were compacted with heavy compactors. Finally, an empirical method, based on long-term measurements of settlement, for predicting shale embankment settlement is proposed and compared to other settlement criteria