Élaboration et implémentation d'un protocole de laboratoire pour l'étude du potentiel de liquéfaction de résidus miniers

ABASTRACT Mining and ore processing produce different types of waste with the most important being waste rock and tailings. The waste product of mineral processing, tailings, consist of very fine grained material in the form of slurry that is placed in impoundments retained by dikes or dams for indefinite storage. In the event of dynamic loading (such as that engendered by seismic activity) tailings are particularly susceptible to liquefaction. Tailings liquefaction presents risks to the retaining structures, which may actually be composed of tailings, and thus risks to the downstream population and environment. Tailings from hard rock, such as encountered in the Abitibi region of Quebec, possess numerous properties that make them susceptible to liquefaction. They tend to be fully saturated, have low density indices and composed of silt-sized particles without cohesion. Due to their saturation and tendency to contract under shear loading, dynamic loadings may result in the development of excess porewater pressures and a resulting decrease in the effective stress. This decrease in the effective stress could result in liquefaction of the material and an increase in the stresses applied to the retention structure. These additional stresses combined with the additional horizontal loading of the earthquake, have resulted in the failure of tailings impoundments. In the evaluation of the potential for liquefaction induced impoundment failure, it is necessary to determine the potential for tailings liquefaction under seismic loading. The objective of this research was the elaboration and implementation of a laboratory protocol for cyclic triaxial testing for the characterization of the dynamic behavior of tailings. The protocol includes a method of specimen preparation that permits complete saturation of the specimen without the use of backpressure that has been shown to significantly influence dynamic behavior during laboratory testing. The experimental program consisted of 8 quasi-static triaxial and 17 cyclic triaxial tests on fine-grained sand from the Demers Quarry (Terrebonne, Quebec) and on tailings from the Canadian Malartic Mine (Abitibi, Quebec).