Geo-Seismic Environmental Aspects Affecting Tailings Dams Failures

Miguel P Romo,Juan M Mayoral

doi:10.3844/ajessp.2008.212.222

Abstract

Seismic performance evaluations of tailings dams are essential for characterizing the geo- environmental risks posed by these earthen structures, which should include the geotechnical hazards implied by slope instability failure, free board loss and the potential release of contaminants. The observed damage is more important when liquefaction occurs on the dam body and foundation, which often leads to cracking, settlements, tilting and general distortion of dam geometry. Analyses based on limit equilibrium are generally sufficient to establish hazard zones. However, numerical models with solution schemes formulated in the time domain, which are capable of taking into account the kinematics of soil movement more realistically, are needed to quantify the geotechnical risk. This paper reviews the main geotechnical earthquake engineering aspects to account for when designing tailings dams and describes the application of a practice-oriented simplified constitutive model, which implemented in a lagragian finite difference platform, is capable of predicting the accumulation of pore pressure in fine-grained saturated materials due to earthquake loading, the reduction of shear strength and the corresponding permanent displacements. The model uses the Mohr-Coulomb failure criterion coupled with an incremental pore pressure generation scheme. Pore pressure is accumulated as a function of the number of stress cycles. The secant soil stiffness and hysteretic damping change with loading history. The numerical simulation is able to properly capture the kinematics of dam failure and provides the parameters to assess potential environmental impacts on the nearby areas of the dam.

Highlights

Mining activity and other industrial processes generate large quantities of solid waste that annually need to be disposed of and stored in the so-called tailings dams in different parts of the world
Among the different aspects to consider in tailings dam design, seismic dam stability analysis is the most relevant in projects located in earthquake prone areas to ensure that catastrophic failures will not occur
Seismic analysis of tailings dam should account for the degree of internal drainage and the characteristics of the design earthquake, to properly estimate the amount of pore pressure built-up during the seismic event, as well as the pertinent impact on the reduction of shear strength and the modification of dynamic soil properties

Summary

INTRODUCTION

Mining activity and other industrial processes generate large quantities of solid waste that annually need to be disposed of and stored in the so-called tailings dams in different parts of the world. Seismic analysis of tailings dam should account for the degree of internal drainage and the characteristics of the design earthquake, to properly estimate the amount of pore pressure built-up during the seismic event, as well as the pertinent impact on the reduction of shear strength and the modification of dynamic soil properties (i.e., shear stiffness and damping) Based on these evaluations, proper assessment of the volume of material mobilized during a potential failure and the pattern and speed of deformation can be achieved, thereby providing guidance to estimate the extension of the affected zones. This study reviews some of the key geo-seismic environmental aspects to consider during seismic evaluations of tailings dams and presents a practiceoriented numerical scheme which, implemented on a lagragian platform, appears to capture the overall behavior of ground response in geotechnical problems well in which large deformations are likely to occur, such as liquefaction or cyclic mobility This approach enhances the formulation proposed by Dawson et al.[8].

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Background

Findings

CONCLUSIONS