Impact of methods used to reconstitute tailings specimens on the liquefaction potential assessment of tailings dams

Mariana Martins Corrêa,Waldyr Lopes Oliveira Filho

doi:10.1590/0370-44672018720164

Mariana Martins Corrêa, Waldyr Lopes Oliveira Filho

Open Access

https://doi.org/10.1590/0370-44672018720164

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Abstract

The aim of this research is to investigate the liquefaction susceptibility of silt sandy mining tailings by experimental laboratory techniques. The main aspect analyzed is how techniques of sample reconstitution impact the results obtained in static undrained triaxial tests. Different methods of sample preparation are reviewed, such as moist tamping (MT), air and water pluviation, and a newly developed one called the Slurry Deposition (SD) method. This research highlights the importance of the "fabric" or particle structural arrangement associated with the various specimen preparation techniques when liquefaction potential assessment is of concern. Two series of undrained static triaxial tests were performed on specimens prepared according to MT and with SD techniques on specimens in the loose and very loose state. Results have demonstrated that MT specimens have shown the whole spectrum of liquefaction resistance (total liquefaction, limited liquefaction, and no liquefaction) on increasing density, while the SD campaign has shown only liquefaction resistance even in the overlapping intermediate densities with the MT series, where the latter has shown liquefaction, although limited. This scientific study critically discusses the risk of taking laboratory results of replicated soil elements that may not correspond to the reality.

Highlights

Laboratory tests play an important role in understanding the mechanical response of geomaterials
The main results of this research are related to the analysis of CIU triaxial tests performed on the silt sandy tailings, whose specimens were prepared according to the moist tamping (MT) and slurry deposition (SD) methods
The present research established an experimental program to assess the mining tailings liquefaction potential through isotropically consolidated undrained triaxial tests. It was driven by the challenge of searching for the most adequate specimen reconstitution method that could make it possible to produce soil elements with a similar structure, as in tailings dam deposits, such as those found in mines in the Quadrilatero Ferrifero of Minas Gerais, Brazil

Summary

Introduction

Laboratory tests play an important role in understanding the mechanical response of geomaterials. For this purpose, testing undisturbed samples obtained from field investigations is considered more appropriate for studying natural soil behavior, since it allows the structure of soil particles in situ, stress field, depositional history, etc. The use of reconstituted samples of granular soils for laboratory testing has gained widespread acceptance in the past for a number of reasons, including (Khalili and Wijewickreme, 2008): a) difficulties in obtaining high quality undisturbed non-cohesive field samples; b) need to test essentially identical "homogeneous" test specimens (without variability commonly found in field samples); and c) demand to characterize manmade engineering materials. Previous articles on this issue have shown that each sample preparation method renders a specific fabric, which may result in distinct stressstrain characteristics and responses (Vaid and sivathayalan, 2000; Carraro and Prezzi 2007)

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