CONSTRUCTION AND MAINTENANCE OF EMBANKMENTS USING HIGHLY ERODIBLE SOILS IN THE PILBARA, NORTH-WESTERN AUSTRALIA

Abstract

Many soils and sediments in the Pilbara region of north-western Australia are highly susceptible to erosion. Large quantities of construction materials are required as iron ore mining and the extensive railway lines used to transport ore to port continue to be developed in the region. Simply avoiding the use of highly erodible materials is often considered to be too high a cost where alternatives are scarce. Constructing embankments to survive the cyclonic wet season from material highly susceptible to erosion, is a major challenge. Highly erodible materials encountered in the Pilbara include some bedrock shales, dispersive alluvial silts and sands and slaking clays and mudstones. Dispersive materials can erode internally by the formation of pipes or tunnels. Piping erosion can be difficult to detect and can cause severe internal damage to embankments before being detected. Similarly, slaking material can undergo compaction during wetting and drying cycles resulting in unexpectedly large settlements. The effect of erosion, in general, is controlled by appropriate embankment design and construction, in particular compaction standards. Erosion controls include sacrificial batters, surface protection, encapsulation and stabilisation. For many mining projects achieving short-term construction deadlines is a high priority and adding erosion control measures after construction may be preferred. Predicting the time by which erosion control needs to be installed or rehabilitated should be a part of the embankment design process. Material selection has direct implications for the on-going asset management of embankment structures.