Mechanical properties of soft tailings from different depths of a Swedish tailings dam: Results from triaxial tests

In an upstream tailings dam, loose layers might occur at different depths due to the melting of frozen layers deposited during freezing temperatures in Sweden. The reduced shear strength of such layers in a tailings dam might cause stability problems. Due to the slow consolidation process, it remains to be seen whether self-weight of a high tailings dam could affect the strength and stiffness of soft tailings located at different depths or not. For numerical modeling, appropriate strength and stiffness properties of soft tailings are required. To this end, loose layers in an upstream tailings dam were identified based on the results of cone penetration tests. Consolidated Drained (CD) triaxial tests were conducted on undisturbed soft tailings collected from different depths of the dam. The results indicated that depth did not have considerable effect on the strength and stiffness of tailings. Hardening Soil Model (HSM) at high confining pressures and axial strains underestimated the stiffness of soft tailings under CD triaxial state. This study shows that (i) proper care is required for evaluating strength and stiffness parameters for soft tailings and (ii) the application of the HSM is likely to predict more deformations, which could give an early warning before an actual failure of a tailings dam. (C) 2020 Sharif University of Technology. All rights reserved.