Sustainable design and construction in Western Sydney: repurposing tailings dams for industrial commercial development in Western Sydney

Tailings is a waste product of quarrying, and it is typically very soft in consistency, highly compressible and therefore makes it undesirable for any development. Without appropriate treatment, development over tailings likely results in unacceptable settlement under loading. This paper illustrates the design of ground treatment adopted on one of the tailings dams in Western Sydney, which was previously used as settlement ponds for a sand quarry. The adopted ground treatment design comprised a combination of vertical drains/wick drains and preload of varying height depending on the characteristics and thickness of the tailings. The wick drains spacing and preload height were first determined based on the in-situ testing results (i.e. CPT and test pits). The novel approach adopted in the design verification involves utilising the wick drains installation equipment to help characterise the site and confirm the assumptions adopted in the design. The wick drains installation records provide a detailed coverage of the depth of the tailings based on the installation resistance and is a pseudo-indicator of the tailings consistency. Additionally, monitoring results were used to validate the design predictions and inform if any design changes are possible during construction (e.g. shorter preload duration).