Experimental and numerical analysis of a slurry consolidation test on tailings

The deposition of fine-grained tailings as a somewhat thickened slurry remains the norm, and presents challenges in the assessment of their geotechnical parameters and the analysis of their settling and consolidation behaviour. The conventional oedometer and Rowe cell consolidometer are not suitable for testing tailings from a slurry state. In this paper, silty sand-sized gold tailings of low plasticity are tested in an instrumented slurry consolidometer and their consolidation is simulated numerically. The purpose-built slurry consolidometer measures 150 mm in diameter and 410 mm in height, and is instrumented with top and base load cells, seven pore water pressure (PWP) transducers starting from the base and spaced at 40 mm intervals spirally up the side of the consolidometer, and a displacement transducer. Up to 560 kPa stress can be applied to the top of the sample, equivalent to about 60 m depth of tailings. The tailings were placed in the slurry consolidometer in a series of layers at an initial 25% solids concentration by mass, and each layer was allowed to settle and the surpernatant water removed before the next layer was placed. Stepwise loading was then applied, since this is the conventional means of loading in a consolidation test, and is the basis of the available numerical analysis software. The difference with the slurry consolidometer over conventional consolidation testing is that the test can commence from a slurry state and follow the largestrain consolidation process. The numerical simulation of a large-strain consolidation problem is challenging due to extreme mesh distortions during numerical calculations. The emerging and innovative material point method (MPM) was used to numerically simulate the consolidation of the tailings from a slurry state. The analysis was carried out using the code and software developed by the MPM Research Community, Anura3D, focussing on PWP dissipation and the resulting consolidation. This numerical approach captured the consolidation behaviour well and provided a reasonable match with the experimental results