Behavioural analysis of iron ore tailings through critical state soil mechanics

Silva, João Paulo de Sousa; Cacciari, Pedro Pazzoto; Torres, Vidal Felix Navarro; Ribeiro, Luís Fernando Martins; Assis, André Pacheco de

doi:10.28927/SR.2022.071921

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Article • Soil. Rocks 45 (2) • 2022 • https://doi.org/10.28927/SR.2022.071921 copy

Behavioural analysis of iron ore tailings through critical state soil mechanics

Authorship SCIMAGO INSTITUTIONS RANKINGS

Abstract

Understanding the geotechnical properties of iron ore tailings is currently one of the major challenges in the mining industry. With transitions from drained to undrained conditions occurring in seconds, recent dam problems have been a challenge to solve with classical soil mechanics, which provides few means to explain how such phenomena develop. There is also an increasing propensity in technical and scientific circles to seek constitutive models that are based on critical state soil mechanics and that allow for the analysis of tailings behaviour. However, there is still a lack of knowledge and information about the critical state properties of iron ore tailings. The present research experimentally and numerically investigated the effectiveness of modelling the behaviour of iron ore tailings. The aim of these experiments was to assess the critical state parameters of tailings from a significant iron ore operation site in Quadrilátero Ferrífero (Minas Gerais state, Brazil). The results indicated that the selected numerical model (NorSand) was adequate to evaluate the behaviour of the studied mine tailings. The numerical results showed consistent adherence to the experimental results of both drained and undrained tests, with deformations below 5% and samples in which the state parameter had a small magnitude.

Keywords
Critical state; Iron ore; Laboratory tests; Numerical model calibration; NorSand; Tailings

Chemical	Tailings
composition (%)	FT-P1	FT-P2
Fe	25.44	13.48
SiO₂	61.23	80.22
P	0.027	0.016
Al₂O₃	0.79	0.028
Mn	0.021	0.001
TiO₂	0.058	0.001
CaO	0.017	0.007
MgO	0.91	0.16
Calcination losses	0.91	0.16

Tailings	$G s$	Void ratio		Standard Proctor		Atterberg limits			Classification
		$e_{m i n}$	$e_{m a x}$	$ρ_{d}$ (kN/m³)	$w$	LL	PL	PI	USCS
		$e_{m i n}$	$e_{m a x}$	$ρ_{d}$ (kN/m³)	(%)
FT-P1	3.8	0.59	1.13	19	14	NP			ML
FT-P2	3.2	0.6	1.1	18	14	NP			ML
BL-2&1	3.6	0.85	1.31	22	12	NP			ML
Typical	3-4.2			17-19	11-15	NP			ML

Specimen			Initial			Post-consolidation
Test	Condition	Test type	$γ$ (kN/m³)	$γ_{d}$ (kN/m³)	$w$ (%)	Mean effective stress (kPa)	Void ratio ( $e$ )
1	dense	CD	24.5	22.6	8.74	50	0.67
2	dense	CD	24.4	22.5	8.68	100	0.64
3	dense	CD	24.6	22.6	8.82	150	0.62
4	dense	CD	24.5	22.6	8.65	300	0.55
5	loose	CD	17.6	16.7	5.38	100	0.92
6	loose	CD	17.6	16.7	5.56	300	0.85
7	loose	CD	17.7	16.7	5.61	400	0.8
8	loose	CD	17.6	16.6	5.34	600	0.78
9	loose	CU	17.7	16.7	5.9	100	0.94
10	loose	CU	17.6	16.7	5.44	200	0.87
11	loose	CU	17.6	16.7	5.44	400	0.86
12	loose	CU	17.7	16.7	5.61	600	0.84

	BL-2&1	Typical range (*)	Comment
CSL
$Γ$	1.28	0.9–1.4	‘Altitude’ of CSL defined at 1 kPa
$λ_{10}$	0.19	0.03–0.15	Slope of CSL defined on base 10
CSL_a	1.13	-	Parameter for curved CSL analogous to $Γ$
CSL_b	0.23	-	Parameter for curved CSL analogous to $λ$
CSL_c	0.27	-	Parameter for curved CSL analogous to an exponent of the stress level
Plasticity
$M_{t c}$	1.35	1.2-1.5	Critical friction ratio, with triaxial compression as a reference condition
$N_{t c}$	0.20	0.2-0.5	Volumetric coupling parameter
$χ_{t c}$	3.45	2.5-4.5	Relates minimum dilatancy to corresponding $ψ$ , with triaxial as a reference condition
$H$	n/a	50-500	Plastic hardening modulus for loading
$H_{0}$	85	-	Often equal to f( $ψ$ )
$H_{Ψ}$	850	-	$H = H_{0} - H_{ψ} . ψ$
Elasticity
$G$	39 and 70	-	Shear modulus
$G_{e x p}$	0.6 and 0.53	-	Soil property
$v$	0.2 (adopted)	0.1-0.3	Poisson’s ratio

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E-mail: secretariat@soilsandrocks.com

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[1] #Corresponding author. E-mail address: eng.jpssilva@gmail.com