This article studies the undrained behavior of filtered copper tailings in unsaturated conditions under monotonic and cyclic loading at controlled matric suction. Two dry densities with the same water content were used. The material behavior was studied in terms of the increase of saturation, the evolution of suction, and volumetric strain during the transition from unsaturated to saturated conditions. The results show that, during the shearing, suction decreases and the degree of saturation increases, regardless of the type of load applied (cyclic or monotonic). This effect is related to the volume reduction of the air phase during the transition to a fully saturated condition. In terms of undrained shear strength, the evolution of the material is studied in terms of the phase transformation line, comparing its location in saturated and unsaturated cases. Regarding the cyclic strength ratio, the unsaturated condition shows a higher value than the saturated case by about 26% and 58% for the high and low densities, respectively. However, when the volumetric strain is higher than 3% or the double amplitude axial strain exceeds 2%, a cyclic strain localization takes place, leading to an extension failure over the sample.

Filtered tailings piles have better mechanical stability than other tailings disposal alternatives because they operate in an unsaturated condition. However, very few studies have quantitatively assessed the contribution of partial saturation for both self-compaction and mechanical stability. In this article, we evaluate the mechanical stability of a filtered tailing pile, based on an analysis of self-consolidation by material deposition under unsaturated conditions, considering rates of 1 h, 1 day and 4 days. For this purpose, an experimental study was carried out which included oedometric and triaxial consolidation tests in both, saturated and unsaturated conditions. Based on these results, a constitutive soil model was calibrated using the Bishop's effective stress concept, considering the evolution of the effective saturation and including soil-water characteristic curve (SWCC) as a function of volumetric strains. The results show that the proposed modeling strategy provides a reasonable approximation of laboratory paths with a single set of parameters. Additionally, the same approach was applied to model the pile's construction process. In this case, it was observed that the potential failure surface is triggered when the soil reaches a saturation degree of about 65-70%. At and this value, the soil behavior is practically independent of deposition rates, slope inclination and pile height. However, the factor of safety (FoS) decreases for faster deposition rates compared to slower ones.

Tailings volumes continue to collectively increase worldwide, leading to larger dams and tailings management facilities. With numerous high-profile dam failures in the past decade, the risks of these management practices are also growing. A potential shift to waste management practices at mineral mines is to commingle waste rock and dewatered tailings. This blended material should have superior physical strength properties provided by the waste rock together with improved chemical stability characteristics associated with the low permeability of the tailings. Ideally, commingled tailings and waste rock can be used to construct various mined earth landforms that are both physically and chemically stable, which will enhance operational performance and ultimately provide for the sustainable decommissioning and closure of the mining facility. To study these materials, the University of Alberta Geotechnical Centre is working with global industry partners to test commingled materials from several mine sites with varying ore and host rock types and climate regimes. The first stage of this study is described here and is focused on the optimum density, saturated hydraulic conductivity, and soil-water characteristic curves of various blend ratios, performed at laboratory scale.