Abstract
Knowing the evolution of water content in a tailings dam is essential when analysing its stability. The case study is a small tailings dam abandoned more than 50 years ago, located in the Andes region of San Juan province, Argentina, where the climate is arid. This paper presents the results obtained in a plot test to study the interaction of tailings with the atmosphere, and to explain the reasons that generate internal zones in the dams with surprisingly high degrees of saturation, despite the strong water deficit of the site. The plot was hydraulically isolated on the four lateral faces where ten capacitive sensors were installed at different depths (volumetric moisture, matrix suction and temperature). At the beginning of the test, a major rainfall event was simulated with a sprinkler irrigation system. The plot was then allowed to interact freely with the atmosphere for an additional period of one and a half years. The records obtained suggest that the stratigraphy of the hydraulically deposited tailings has a preponderant influence on the interaction with the atmosphere. Heterogeneous flow phenomena and multiple capillary barriers during the infiltration and evaporation processes, respectively, appear to control the long-term moisture state of the tailings dam.
Highlights
Very thin layers of tailings are formed by the superposition of discharges from different points (Figure 1)
It is possible that the pattern of small cracks observed in this layer has a determining influence on the infiltration. It has been observed in laboratory experiences that the networks of preferential pathways created by the cracks and interfaces between the thin layers can generate variations of permeability of more than an order of magnitude if the same homogeneous tailings package is taken as a reference (Rodríguez 2002 [29], Rodríguez and Oldecop 2006 [30])
The tailings studied have a stratigraphic profile composed of very thin layers, where grain size alternate between silt (ML), clay (CL) and fine sand (SM)
Summary
In contrast to most civil engineering works, tailings dams are designed to last indefinitely over time. This is a real challenge when it comes to assessing their structural safety. Open-pit mines currently generate large amounts of waste, with mining tailings being one of the most important in terms of volume, exceeding all previous experiences in civil engineering fills of any kind. Water management in tailings dams is a key factor for their safety (ICOLD 2001 [10], Davies 2002 [11], Bligth and Fourie 2005 [12], Rico et al 2008 [13]). Historical cases of failures caused by very diverse factors and mechanisms (landslides, earthquakes, overtopping, piping and failure of auxiliary structures), show thatthe hydraulic operating conditions play a key role in the development of the failure, as well as in the magnitude of its consequences (Oldecop et al 2008 [14])
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