Effects of Stress State on the Cyclic Response of Mine Tailings and its Impact on Expanding a Tailings Impoundment

Effects of Stress State on the Cyclic Response of Mine Tailings and its Impact on Expanding a Tailings Impoundment

Author: Michael F. Riemer, Jorge Macedo, Orlando Roman, Solange Paihua
Conference: 3rd International Conference on Performance-based Design in Earthquake Geotechnical Engineering (PBD-III)
Date: July 16-19, 2017

ABSTRACT
In order to increase the capacity of an existing mine tailings impoundment in the Peruvian Andes, a rockfill dike which will be partially supported on different types of older tailings is being raised. Achieving adequate performance during and after possible seismic loading requires a thorough understanding of the cyclic (and post-cyclic) response of these different foundation materials over a range of consolidation stress levels and static shear conditions. In addition, one or more methods of ground improvement will be assessed to be applied to limited sections of the foundation to improve the system performance, and this is expected to play an important role in its seismic stability.

The current paper focuses on the characterization of the two primary tailings deposits. This includes the cyclic response over a range of stress conditions, the compressibility and its implications for liquefaction potential after construction of the dike, and the likely settlements to be expected after shaking. The laboratory program performed includes undrained cyclic simple shear testing under both the current and projected stress conditions after expansion, consolidation testing under conventional and post-cyclic conditions, and assessment of the steady state relationship of these materials. These results are complemented by cone penetration tests and borings from the field.

Given their current state and the seismic environment, both the coarser, tailings deposit and a finer-grained deposit are capable of large pore pressure generation and excessive shear deformations. While the response of the coarser material is much like a conventional sand, the finer-grained tailings are significantly more compressible, and this appears to alter the liquefaction potential under differing stress conditions in less predictable ways. Understanding how these tailings will respond to the elevated confining stresses and static shear stresses beneath the new dike is critical to analyzing potential designs, and insuring the safe development of this facility.

 

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