This paper covers the investigation, design, construction and performance of a tailings dam at Mount Thorley Warkworth (“MTW”), a Coal and Allied operated open-cut coal mine in the Hunter Valley, NSW.

A tailings disposal site was identified in one of the ramps through the mine-spoil piles. The “foundations” and abutments comprise uncompacted mine spoil to a depth of 40m below the haul road surface. The Stage 1 embankment at this site has a height of 70m.

The dam is a zoned rockfill embankment, constructed from mine spoil. It was designed as a “leaky” dam. An innovative method of work packages was developed for construction. The rockfill was delivered to the site by the mine. Spreading and compaction was carried out by a separate external contractor. Construction of the embankment was completed in a period of 5 months.

Filling of the storage commenced before the end of construction. Monitoring has included measurements of very large settlements, plus tailings level and piezometric surface. The monitoring results are presented and discussed.