Abstracts Engineering

Behavior of mine tailings dams under high tailings deposition rates

by Caius. Priscu

One of the challenges mine operators have to face in large surface tailings disposal projects is to keep high tailings deposition rates under allowable values, while ensuring a sound and stable surface impoundment This is particularly important in the case of the upstream method of construction, in which perimeter dikes overlay soft unconsolidated deposits of fine materials (usually silts and days), where loss of shear strength could develop due to excess pore water pressure build-up. This study offers a new approach for investigating the influence of tailings deposition rate over the structural behavior of upstream tailings dams, and its relation to the construction sequence and pond operation. A complex, yet practical method uses a nonlinear numerical algorithm, integrating a 1-dimensional self-weight consolidation model for fine grained materials, with a 2-dimensional stress-deformation finite element program for consolidation of earth structures. A beach profile equation is used to complete the structural geometry of the dam at various operating stages. The dam behavior is evaluated based on excess pore water pressure profiles, principal effective stress levels, and mobilized material strength. The time-dependent pond filling operation process and staged dam construction are simulated. A case study from a large operating South African gold mine is used to perform simulations and parametric analyses. The behavior of the upstream tailings dam is assessed under both normal and increased slurry discharge rates. It is shown that under variable deposition rates, the present approach can help identify weak structural zones, and hence, improve the assessment of the structural dam safety. From such analyses, adequate tailings deposition rates conditions could be determined in advance for a variety of mill or pond operating conditions.