Evaluation of the Static Liquefaction Behaviour of Silty Tailings in Unsaturated Conditions

Tailing wastes are the products resulting from mining processes, consisting of a mixture of silt, clay and sand with variable quantities of water, chemical reagents and unrecoverable metals. They are usually discharged into storage areas known as tailing dams or tailing storage facilities (TSF), characterized by a wide surface exposed to the atmosphere whose interaction governs the position of the water table within the basin, and so the extension of the unsaturated zone above the phreatic surface. A detailed knowledge of the hydro-mechanical response of the discharged tailings represents a fundamental tool to reliably assess the stability of tailing dams to minimize the high rate of recent failures in which static liquefaction has been widely recognized as one of the major causes of dam collapse. Moving from these reasons, this research presents the main overcomes of an experimental campaign to investigate the static liquefaction response of silty tailings collected after the collapse of the Stava dams. The mechanical response of Stava tailings was studied by performing monotonic triaxial tests. The dependency of the static liquefaction behaviour on the sample preparation technique and on the degree of saturation (B-Skempton parameter) was investigated. The sample preparation method and degree of saturation were shown to affect the static liquefaction strength of the Stava tailings. The experimental results were in accordance with data from literature, and the Critical State Line of the unsaturated Stava tailings was compared to those given by the same tailings in saturated conditions.