Unsaturated behaviour of tailings during deposition and desiccation cycles with reference to closure design

The conventional deposition of mine tailings as a slurry in seepage, with the potential to contaminate surface and ground waters, particularly during deposition, and possibly post-closure. In a dry climate, tailings deposition can be cycled to largely evaporate excess water, and on closure the tailings may remain desiccated to the extent that incidental rainfall will not result in continued seepage and contamination of the surrounding environment. To provide supporting information for the selection of appropriate closure design criteria, and to provide information relating to the unsaturated behaviour of tailings during deposition and desiccation cycles, a trial tailings cell at a mine in arid Western Australia has been instrumented with moisture and suction sensors located on towers placed prior to tailings deposition. Tailings were deposited over 18 months in a series of lifts and the resulting desiccation and rewetting cycles were monitored by the instrumentation. This paper describes the life cycle of tailings deposition and desiccation, presents the moisture and suction data collected during the deposition and desiccation phases, provides a commentary on the results, and recommends some design parameters for the design of a suitable cover system for the tailings storage facility (TSF) at the site