Static liquefaction response of silty tailings in nearly saturated conditions

Tailing storage facilities are complex geotechnical systems 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 tailings is fundamental to reliably assess the stability of the tailing dams to exclude the onset of static liquefaction which has been recognized as one of the major causes of dam failure. This research gives the main overcomes of an experimental campaign to study the static liquefaction behaviour of silty tailings collected after the failure of the Stava basins. Monotonic triaxial tests were performed to investigate the static liquefaction response of tailings in nearly saturated conditions in terms of stress-strain behaviour. The dependency of the static liquefaction strength on the sample preparation technique, the void ratio and the degree of saturation was investigated. The degree of saturation and the sample preparation method were proved to affect their static liquefaction strength while, upon certain values, the initial density was not the main factor affecting the hydro-mechanical behaviour of tailings under investigation. Some theoretical relationships between the –B Skempton parameter and the degree of saturation with the respective experimental values were also compared. The experimental data collected in the present research during the saturation phase of the sample were in good agreement with the theoretical formulations proposed by Reuss and with those given by Lade and Hernandez. The Critical State Line (CSL) of the nearly saturated Stava tailings was successfully compared with those obtained by the same soil in saturated conditions.