The Shear Strength of Filtered
Tailings and Waste Rock Blends
Ralph Burden
Dr David J. Williams
Dr G Ward Wilson
Michael Jacobs
1 October 2018
| Geotechnical Engineering Centre
• Introduction
- Filtered tailings
- Benefits of adding rock to filtered tailings
- Objectives
• Background
- Previous research on shear strength of waste rock
/ tailings blends
• Test Method
• Blending and Material Properties
• Results
• Conclusions
Outline
2
Introduction: Filtered Tailings
3
Slurry
≈ 30% Solids
Thickened
≈ 55% Solids
Filtered
≈ 85% Solids
What are the Potential Benefits of Adding Rock to a
Filtered Tailings Stack?
4
• Increased shear strength
• Steeper side slope, better stability
• Increased hydraulic conductivity
• Faster dissipation of excess pore pressure generated during
stacking
• Material can be stacked faster, in higher lifts
• Lower moisture content / degree of saturation
• Less pore pressure, better stability
• Less requirement to dry filter cakes before spreading and
compacting, faster stacking
• Increased density
• Lower overall waste volume
Focus of this presentation
Objectives
5
Objective: Investigate the influence that addition
of rock has on the shear strength of filtered
tailings
Key questions:
• Does adding rock to a stack increase shear
strength?
• What is the relationship between mix ratio and
shear strength?
Background: Blended Co-disposal
6Wilson, G. W. W., B.; Miskolczi, J. (2008). Design and Performance of Paste Rock Systems for Improved Mine Waste Management. First
International Seminar on the Management of Rock Dumps, Stockpiles and Heap Leach Pads. Perth, Australia, Australian Centre for
Geomechanics.
Blend Configurations (After Wickland 2006)
7
Rock
Pure RockPure
Tailings
Increasing Mix Ratio
“Floating”
Condition
“Just-filled”
Point
Unsaturated
Condition
Previous Research on Shear Strength of Blends
8
Pure RockPure
Tailings
Increasing Mix Ratio
“Floating”
Condition
“Just-filled”
Point
Unsaturated
Condition
Shear strength
equivalent to rock
alone?
Rock
Test Method
9
• 300 x 300mm shear box
• Confining stresses of 250,
500 and 1000 kPa
• Strain rate: 0.1 mm/min
(fully drained conditions)
• Tested at blended
moisture contents
Materials Tested
10
Waste Rock
w = 2.1%
Filtered Tailings
w = 19.3%
Blending and material properties: Mix ratio
11
All mix ratios are expressed as Rock : Tailings by
dry mass
Three mix ratios tested:
• 0.4 : 1
• 1 : 1
• 1.8 : 1
Tests were also carried out on tailings alone and
waste rock alone
“Floating” Condition
- Approximately “Just Filled” point
Waste Rock Scalping
12
Large particles must be
removed due to
constraints in shear box
size
• Waste rock scalped
on-site to -100 mm
• Scalped to -37 mm for
testing
Particle Size Distribution
13
Particle Size Distribution
14
Blending Procedure
15
• “Perfect” blending
targeted to achieve good
quality, repeatable results
• Water added if required to
bring material up to field
moisture content
Blending Procedure
16
Blending Procedure
17
Blending Procedure
18
Results
19
Conclusions
20
• Adding waste rock to tailings increases shear
strength:
- Up to a limiting mix ratio of about 1:1 R:T
• At high stresses, strength of mixture is higher
than strength of waste rock alone:
- Addition of filtered tailings increases point
contacts, reducing breakdown of waste rock
Questions?
| Geotechnical Engineering Centre