Engineers Australia

Slope failure mechanisms in hydraulically placed coarse sand tailingsBaden Clegg Award entry

Brendan G. Wright

Abstract

Coarse sand tailings deposited during the mineral sands mining process can often contain varying quantities of clay and silt sized particles referred to as “slimes”. When placed hydraulically, these slimes can become trapped, resulting in pockets or lenses of sand-slime mixtures within the quartz sand tailings.

Extensive mineral sands deposits exist in Western Australia. The case study for this paper is an active mineral sands mine located north of Perth. Minor slope failures resulting from hydraulically placed coarse sand tailings are not uncommon and have been experienced in the past. Recorded failures at the site have typically occurred beneath pond level or at the overburden tip face resulting in recession of the tailings beach and ground heave at the toe of the tip face. Despite being problematic, these types of failures are not of sufficient magnitude to affect day to day operations and present no risk to employees’ safety.

This paper looks at the effect of these sand-slimes mixtures and the mechanisms responsible for triggering a massive slope failure vastly different to previous failures observed in this type of mining operation. The control measures implemented to reduce risk and minimise the possibility of this type of failure occurring again in the future are also discussed.