Analysis of cyclic testing of tailings using the triaxialsimple shear (TxSS) apparatus

Xavier Archambault-Alwin, Michael James, Mourad Karray, Mohamed Chekired

Dans les comptes rendus d’articles de la conférence: GeoOttawa 2017: 70th Canadian Geotechnical Conference; 12th joint with IAH-CNC

Session: Mining - Hard Rock I

ABSTRACT: The dynamic behavior of tailings was studied using innovative laboratory testing, the triaxial-simple shear device (TxSS). In total, 29 specimens were isotopically consolidated and then subjected to strain-controlled cyclic loading consisting of uniform shear strain amplitudes. Numerical simulations were used to relate the uniform cycles of shear strain to uniform cycles of shear stress by applying an energy approach to correlate the generation of excess pore water pressure to the cumulative energy absorbed by the specimens. This paper presents the methodology employed to analyze the results and obtain the cyclic resistance of the tailings in terms of cyclic resistance ratio. The energy-based approach was validated through additional strain-controlled tests where the applied strains were equivalent to the variable strains produced by numerical simulations of tests with uniform cyclic shear stress amplitude.

RÉSUMÉ: Le comportement dynamique de résidus miniers innovateur, triaxial-simple shear (TxSS). Au total, 29 échantillons ont été soumis à des essais de cisaillement cyclique sous des déformations contrôlées. Les essais ont été réalisés à des déformations cycliques constantes et une variété de contraintes de confinement. Des simulations numériques oapports des contraintes cycliques uniformes attribuables aux déformations uniformes appelées durant les essais. Cet article présente la méthodologie essais, dont lbsorbée par les liques imposées étaient les déformations croissantes observées lors des simulations numériques conduites avec des contraintes cycliques uniformes. 1 INTRODUCTION The rate of failure of tailings dams is 5 to 15 times higher than that of conventional water retention dams (Davies 2002). For example, of 182 tailings dam failures studied in their 2001 report, the International Commission on Large Dams found that more than 18% were attributable to seismic loadings and that seismically-induced liquefaction of the retained tailings was a causative factor in many of these failures (ICOLD 2001). Mine tailings are prone to liquefaction because of their intrinsic properties and the most common method of disposal. Tailings from hard rock mines are cohesionless silts with minor amounts of sand. The hydraulic conductivity of these tailings is generally quite low ranging from 10-6 to 10-4 cm/s. Typically, tailings are transported as slurry through pipelines and deposited hydraulically into basins formed by incrementally raised tailings dykes. The very loose and saturated tailings then consolidate slowly under self-weight as successive layers of tailings are deposited (Vick 1990). The operational lifespans of tailings impoundments typically range from 10 to 20 years. However, there are tailings impoundments that have been in operation for several decades. The continuous deposition of tailings assures that at least some portion of the tailings will be loose and thus highly susceptible to liquefaction during operations. Though the susceptibility to liquefaction decreases with consolidation and ageing, the indefinite post-closure lifespan of tailings impoundments corresponds to an increased risk of the occurrence of significant seismic activity. The dynamic behavior of tailings from a mine in western Quebec was studied using an innovative testing device, the triaxial simple-shear device (TxSS). The objectives of this study are to understand the response of these tailings to seismic loads and to quantify their susceptibility to liquefaction based on readily measured material properties. This paper presents a summary of the laboratory testing, a description of the results and the methodology used to analyze the test results as well as a summary of the findings. 2 TRIAXIAL-SIMPLE SHEAR DEVICE (TXSS) The dynamic testing was conducted at the Soil Mechanics Laboratory of the Université de Sherbrooke under the supervision of Professor Karray. The device is known as

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