The critical state line of nonplastic tailings

L.A Torres-Cruz,J.C Santamarina

doi:10.1139/cgj-2019-0019

Abstract

The probability of failure of tailing dams and associated risks demand improvements in engineering practice. The critical state line provides a robust framework for the characterization of mine tailings. New experimental data for nonplastic platinum tailings and a large database for tailings and nonplastic soils (grain size between 2 and 500 μm) show that the critical state parameters for nonplastic tailings follow the same trends as nonplastic soils as a function of particle-scale characteristics and extreme void ratios. Critical state lines determined for extreme tailings gradations underestimate the range of critical state parameters that may be encountered in a tailings dam; in fact, mixtures with intermediate fines content exhibit the densest granular packing at critical state. The minimum void ratio emin captures the underlying role of particle shape and grain size distribution on granular packing and emerges as a valuable index property to inform sampling strategies for the assessment of spatial variability. Mineralogy does not significantly affect the intercept Γ100, but it does affect the slope λ. The friction coefficients M of tailings are similar to those of other nonplastic soils; while mineralogy does not have a significant effect on friction, more angular grains lead to higher friction coefficients.

Highlights

The historical failure rate of tailing dams and the associated risks demand improvements in material characterization, the design of the containment structure, construction practices, and monitoring technology (Santamarina et al 2019)
This study explores the determination of the critical state line (CSL) of nonplastic platinum tailings, analyzes results in the context of a large database of CSLs compiled from the literature (25 nonplastic tailings and 132 nonplastic soils), and seeks to identify trends between critical state parameters (⌫100, ␭, and M) and index properties that can be used to readily assess spatial variability in tailings dams
Data sources The following analyses take into consideration the critical state lines (CSLs) of the three platinum mixtures described above, 25 tailings reported in the literature (Table 3), and 132 nonplastic soils collected from published studies

Summary

Introduction

The historical failure rate of tailing dams and the associated risks demand improvements in material characterization, the design of the containment structure, construction practices, and monitoring technology (Santamarina et al 2019). The reference stress p* does not affect the critical state line (CSL) in itself, it does affect the strength of the correlations between ⌫p∗ and other parameters (Torres-Cruz 2019). Analyses based on the two extreme gradations underestimate the range of critical states present at a nonplastic tailings dam.

Results

Conclusion