Cyclic shear response of fine-grained mine tailings

Abstract

The mechanical response of three different types of fine-grained mine tailings is examined using data from constant-volume cyclic direct simple shear (DSS) tests. Under cyclic DSS loading, fine-grained tailings typically exhibit a cumulative decrease in effective stress along with progressive degradation of shear stiffness. The observed shear strain development due to cyclic mobility is similar in form to that of the previously observed cyclic shear response for natural silts. The cyclic resistance ratio (CRR) of laterite tailings is observed to increase with an increase in the initial effective confining stress (σ′_vc). For this material, the dilative tendency due to stress densification seems to have overridden the contractive tendency due to the increase in confining stress. In contrast, the CRR of copper–gold–zinc tailings is insensitive to the initial effective confining stress, suggesting a response similar to that of normally consolidated clay. The postcyclic maximum shear strength ratio (S_u-PC/σ′_vc) obtained from constant-volume monotonic DSS tests is noted to increase with a decrease in the void ratio. For the fine-grained tailings considered in this study, the liquefaction susceptibility predicted using commonly used empirical criteria is not always in agreement with the liquefaction triggering determined from cyclic DSS tests.Key words: tailings, liquefaction, cyclic stress ratio, postcyclic shear strength, direct simple shear testing.