Strength of Mintaro Shale

Anthony (Tony) Meyers

This paper presents the results from a series of laboratory tests on the Mintaro Shale. The rock type is commonly referred to as slate due to its immature meta-siltstone status. It has been described as “one of the best slates in the world” for architectural purposes since first being quarried in 1858. However, few studies have ever been carried out to investigate its strength characteristics. This paper presents a series of results from uniaxial and triaxial compression tests, point load tests and tensile tests aimed at addressing this issue. The study showed the slate to be of low anisotropy with respect to compressive strength and of high anisotropy with respect to tensile strength. As expected with an anisotropic rock, the compressive strength and the failure modes are strongly dependent on the orientation of the cleavage with respect to the loading direction. A series of empirically derived equations is presented to enable the compressive strength to be determined at various confining pressures and loading orientations with respect to the direction of cleavage.