Mechanical response of highly gap-graded mixtures of waste rock and tailings. Part II: undrained cyclic and post-cyclic shear response

Mixing of waste rock and tailings as a homogeneous mixture (referred to as 'paste rock') has been suggested as a favourable approach to overcome deficiencies associated with traditional methods of mine waste disposal. In consideration of the current limited understanding of the fundamental mechanical response of paste rock, a laboratory research program was undertaken to investigate the monotonic and cyclic shear response of paste rock. This paper presents the findings from undrained cyclic triaxial shear testing conducted on saturated paste rock specimens reconstituted such that the tailings would 'just fill' the void spaces between the coarse particles of the skeleton. During undrained cyclic loading, paste rock typically exhibited a cumulative decrease in effective stress along with a progressive degradation of shear stiffness. The material generally displayed a higher tendency for strain development under cyclic loading when compared with rock-only and tailings-only specimens subjected to similar consolidation and cyclic loading conditions. However, no strain-softening or loss of shear strength was observed, suggesting that the material is unlikely to experience flow failure under undrained cyclic loading. The cyclic shear resistance was relatively insensitive to the initial effective confining pressure ([σ'.sub.3c]) for the tested stress levels of [σ'.sub.3c] < 400 kPa. Key words: liquefaction, mine tailings, mine waste rock, cyclic shear response, triaxial testing, cyclic mobility. Le melange des roches steriles et des rejets de concentrateur sous forme de pate homogene (appeleepate residus-sterile ou PRS) a recemment ete suggere comme approche de gestion des residus miniers qui permet de contourner certains problemes associes aux approches traditionnelles. Puisque les connaissances sont limiteees dans le domaine du comportement meecanique fondamental de la PRS, une etude en laboratoire a ete initiee dans le but d'eevaluer le comportement en cisaillement monotonique et cyclique de la PRS. Cet article presente les resultats obtenus lors des essais triaxiaux en cisaillement cyclique non drainees effectuees sur des echantillons de PRS satureis reconstituees de telle facon a ce que les rejets remplissent tout juste les vides entre les particules de roches steriles. Pendant le chargement cyclique non draine,la PRS presente typiquement une diminution cumulative de la contrainte effective ainsi qu'une degradation progressive de la rigidite en cisaillement. Le materiau demontre geneiralement une plus grande tendance au developpement de deformations en conditions de chargement cyclique, comparativement aux echantillons de sterile seul et de residu seul soumis aux memes conditions de consolidation et de chargement cyclique. Cependant, aucun relachement des deformations ou perte de resistance au cisaillement n'a ete observe, ce qui suggere que le materiau n'est pas susceptible de subir une rupture en ecoulement lors de chargement cyclique. La resistance au cisaillement cyclique etait relativement insensible a la pression initiale de confinement ([σ'.sub.3c]) pour les contraintes testees de [σ'.sub.3c] < 400 kPa. Mots-cles: liquefaction, residus miniers, roches steriles, comportement en cisaillement cyclique, essai triaxial, mobilite cyclique. [Traduit par la Redaction]
Introduction Mine waste commonly consists of two main waste types: relatively fine-grained tailings and coarse-grained blasted-crushed rock. While fine-grained tailings are typically discharged in slurry form to a tailings impoundment, [...]