CHEMICAL, MINERALOGICAL, TEXTURAL PROPERTIES OF THE KOPE FORMATION MUDSTONES: HOW THEY AFFECT ITS DURABILITY

Slope failures are a common and longstanding problem in Cincinnati, Ohio. Most are associated with the Kope Formation, a rock unit characterized by meter-scale cycles of mudstones and limestones where thick mudstone is sandwiched between two thinner limestone layers. This study evaluates chemical, mineralogical and textural properties of Kope mudstones to determine why it is less durable than other formations. A two-cycle slake durability test was performed on thirty mudstones samples belonging to three consecutive cycles of the Kope Formation from a fresh outcrop in Newport, Kentucky. Chemical and mineralogical analysis of the bulk sample and the sludge (slaked portion of the rock after second run) were determined using X-ray fluorescence and X-ray diffraction and the data were compared with the two-cycle slake durability index (ID₂). Individual chemical constituents and mineralogy do not show any significant relationship with the ID₂ of mudstones. Two main fabric types of mudstones were seen in the field - laminated and non-laminated. Detailed micro-fabric characteristics of the samples were observed using the scanning electron microscope. Laminated mudstones with turbostratic or parallel packet type fabric showed higher slake durability and lower moisture content than the non-laminated mudstones with matrix or book-house type fabric. According to the “Two-sample t-test” there is a significant difference in the ID₂ of the two types of mudstones. Laminated mudstones have a high ID₂ compared to non-laminated mudstones. Because the two mudstones types have different geotechnical properties and both types exist in many cycles of the Kope Formation, care should be taken to select core samples from both fabric types for preliminary tests in geotechnical practice. This will provide more accurate estimations of the geotechnical properties of the Kope Formation mudstones.