Engineering Properties of Permian Clay Tuffs

The economic Permian coal deposits of the Newcastle Coal Measures of Eastern Australia are characterized by frequent tuffs and tonsteins, of predominantly clay character. Compared with their associated sedimentary rocks, these have undesirable engineering properties. This paper describes the results from a series of studies undertaken to characterize these materials in their context as engineering materials. The large number of tuff units throughout the coal measures are found to vary greatly in their composition and texture, with many being dominated by high plasticity, expansive clays. This makes them difficult to compact, with low dry densities and high optimum water contents. Their treatment as earthworks materials is reviewed and data is presented which quantifies variability in their engineering properties, as determined from a major earthworks project. Methods of successfully incorporating them into earthworks designs are discussed.