Relationship between fissility, composition, and engineering properties of selected shales from Northeast Ohio

Engineering behavior of shales is extremely variable and is markedly influenced by their structure and composition. To investigate in detail the influence of structure and composition, fresh shale samples with varying degrees of fissility were collected from ten exposed sites in Northeast Ohio. The shales and siltstones ranged in age from Upper Devonian to Pennsylvanian. Based on their breaking characteristics, representative samples from each site were ranked as least fissile, moderately fissile, and highly fissile. A series of laboratory tests were performed to determine the engineering properties of each shale. Compaction tests were performed on each shale individually. Fissility showed no apparent relationship with the natural water content, silt and clay content, durability characteristics, and unconfined compressive strengths of compacted samples. The unconfined compressive strength decreased with increasing proportions of siltstone up to 60 percent siltstone content, after which the strength increased with increasing proportions of siltstone.--Modified journal abstract.