Engineering properties of the Newer Volcanics basaltic clays

The Newer Volcanic basaltic clays, weathered from the Newer Volcanics basalt rock, are commonly found to the north and west of Melbourne. As the Newer Volcanic basalt flow was the predominant overlay rock in the Western and Northern suburbs, the weathered basaltic soil is at a prime depth for shallow foundations of light structures. These basaltic clays can cause significant engineering problems for light structures and buried infrastructure. The shrinkage and swelling of basaltic clays due to seasonal moisture content change can damage light structures and buried infrastructure by movement in the foundation base and subsequent building movements. These movements can result in cracks and fissures within the clay as well. To date the weathering and soil formation, Atterberg limits and compaction efforts are well known for typical Victorian basaltic clay, however testing information is rarely published, and to a lesser extent mineralogy, soil strengths and swelling of the clay are not well documented. This paper discusses the reactivity of basaltic clays and examines engineering properties of the Newer Volcanics basaltic clays in Victoria based on previous testing and literature. The properties are: Atterberg limits, mineralogy, shear/ tensile strength testing, drained friction angle, permeability, suctions and shrinkage testing. Data are combined from testing and from literature conducted throughout Victoria.