Engineering geology considerations for development on Bringelly Shale in Western Sydney

Western Sydney is expected to undergo a substantial transformation over the coming decades, with planning for extensive residential developments and significant infrastructure projects. This rapid urban expansion requires a thorough understanding of the engineering geological behaviour of significant geological formations, in particular the Bringelly Shale. This formation is known for its high potential for shrink-swell behaviour and susceptibility to rapid degradation when exposed to wetting and drying cycles, and further exacerbated by human activities, such as excavation and earthworks, which disrupt its equilibrium state.

This paper shares project experiences to inform construction practices in the Bringelly Shale and highlights the importance of incorporating engineering geological practices. A case study demonstrates the value of developing an engineering geological model to evaluate the combined impact of removing protective sandstone caps on hills containing Bringelly Shale and the influence of subvertical joints, excavation and rainfall infiltration, in the rapid degradation of subsurface materials and impact on slope stability. Similar lithological conditions can be expected throughout Western Sydney.

Additionally, this paper outlines key considerations (e.g., identifying backfilled farm dams, understanding saturation zones, and soil creep) which should be assessed in early phase planning and design when working in Bringelly Shale, to manage and mitigate significant risks to foundation design, deep excavations, and linear infrastructure. Early identification of these risks is essential for informing planning decisions and guiding necessary investigations to support effective and safe design practices.