Index properties and the engineering behaviour of Bringelly Shale

This paper is concerned with the engineering behaviour of Bringelly Shale and how this can be assessed based on laboratory index tests that are widely used for argillaceous rocks. Comparison will be made with data from Ashfield shale to indicate the differences between these two members of the Wianamatta Group. It is shown that Bringelly shale contains reactive clay minerals, absent in Ashfield Shale and, as a result, the shale is more sensitive to changes in environmental conditions. Bringelly Shale is only weakly cemented and its strength and stiffness are lower than Ashfield Shale. Both shales have similar unconfined compressive strengths, typically between 10 MPa and 50 MPa, but in Bringelly Shale a large component of this strength appears to be derived from pore water suctions. When Bringelly Shale is placed in water it disintegrates. The paper concludes with some implications of the data for construction in Bringelly Shale.