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