Long-term environmental stability of borrow pits in highly erodible soils in the Pilbara

The regulatory controls on long-term management of borrow pits in the Pilbara region of north-western Australia typically require a 'free-draining' final configuration. This requirement is not compatible with the many soils in the Pilbara region which are highly susceptible to erosion. As the region continues to develop as a focus of iron ore mining and construction of related infrastructure, environmental management of local earthworks excavations will need to be appropriate to the erosional characteristics of the local soils and sediments. In particular, railway lines used to transport ore to port require the excavation of extensive borrow pits which must withstand an environment which includes extremes of wet and dry seasons including being located in one of the most cyclone-prone areas of Australia. The coastal alluvial sediments are dominated by the silty 'pindan' sand which is highly prone to erosion. Field observations and laboratory testing shows that the pindan sand contains dispersive clays, even where clay content and sodicity is low. Analysis of exchangeable cations in samples of the silty sand show that the dispersive behaviour could be controlled by lime and/or gypsum additions.