Desiccation in dewatering and strength development of high-density hard rock tailings

Abstract

The time for a freshly deposited layer of high-density tailings to reach a given water content and the contribution of desiccation to the geotechnical behaviour of the stack are complementary pieces of information. Generic modelling analyses to predict dewatering time, first presented at the 13th International Seminar on Paste and Thickened Tailings in 2010 (Paste 2010), are compared with a laboratory simulation of multilayer deposition and select field data. The multilayer experiment supports the finding of the generic modelling predictions: the rate of dewatering decreases over time, as evaporation can be supplied by water from the underlying pre-desiccated tailings. Geotechnical behaviour is discussed using results from simple shear and vane tests on samples with different degrees of desiccation and different levels of subsequent consolidation. Desiccation appears to substantially increase strength and imparts strain hardening behaviour to tailings even after they are re-saturated and consolidated. Substantial increases in strength occur well before the shrinkage limit is reached. Finally, the relevance of shear strength development to overall stack geometry and beach angle is briefly discussed.

Integrating Site Conditions, Rate of Rise and Deposition Sequence to Beach Slope Estimations for High Thickened Tailings

“…Since evaporation after shrinkage limit is low (Wilson, 1994), then extra time for Tinactive2 could be represented as Eq 16. If more desaturation is required, for achieving enhanced residual strength or cyclic resistance to liquefaction (Simms, et. al 2013), this Tinactive2 can be increased.…”