Geotechnical properties of iron
mine coarse tailings
M. Esfehani, N.S. Verma, J. Lemieux, and T. Hamade
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Conference Sponsors
AMEC Earth & Environmental
Knight Piésold and Co.
Ausenco
MWH
BASF Chemical
MineBridge Software, Inc.
CETCO
Paterson & Cooke
ConeTec
Robertson GeoConsultants, Inc.
DOWL HKM
SRK Consulting, Inc.
Engineering Analytics, Inc.
Tetra Tech, Inc.
Gannett Fleming
URS
Golder Associates, Inc.
Community Sponsor
CDM Smith
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Context
 Investigation of
geotechnical
properties of
coarse tailings at
Bloom Lake Iron
Mine
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Context
 Coarse tailings are utilized in the construction of
various structures at the Mine
 Geotechnical design process requires:
•
•
Evaluation of dykes and stockpiles stability
Forecast of geotechnical behavior
 Stability analysis requires determination of mechanical
and hydraulic properties of tailings
 Characteristics of the tailing materials are influenced
by:
•
•
Nature of parent rock
Production and disposal processes
 Site specific investigation
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Investigation program
 In situ activities


Sampling
In situ measurement
 Lab testing







Grain size distribution
Specific gravity
Minimum density
Permeability
Direct shear test
Consolidated undrained (CU) triaxial test
Scanning Electron Microscope (SEM) imaging
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In situ activities
 Sampling program
 In situ density measurement
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In situ activities
 Sampling program in deposition area
 Hydraulic deposition process


Large particles settle faster than the fines
Grain size distribution is a function of distance from
discharge point

Sampling at three locations along discharge stream:
• Near the upstream end
• At midstream
• Near the downstream end
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In situ activities
 Samples
• Upstream
•
•
Midstream
Downstream
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In situ activities
 In situ density measurement
 Obtaining representative density values
 Determining the target densities for the laboratory
testing program
• Available data from the previous and ongoing
construction of the tailings dykes
• Measurements at roller compacted area (dykes)
• Measurements at dozer compacted area (tailings)
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Lab testing program








Grain size distribution analyses
Specific gravity determination
Minimum density determination
Permeability tests
Proctor tests
Direct shear tests
Consolidated undrained (CU) triaxial test
Scanning Electron Microscope (SEM) imaging
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Lab test results
 Grain size distribution
Sample location
Fines (%)
(particles < 75 µm)
Upstream
6
Midstream
8
Downstream
15
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Lab test results
 Specific gravity
Sample location
Specific gravity
Upstream
3.30
Midstream
2.90
Downstream
2.87
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Lab test results
 Minimum density
Sample location
Minimum dry density (kg/m3)
Upstream
1,776
Midstream
1,507
Downstream
1,383
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Lab test results
 Permeability
Sample location
Permeability (m/s)
Upstream
1.09 x 10-5
1.17 x 10-5
Midstream
1.18 x 10-5
2.25 x 10-5
Dowstream
1.88 x 10-5
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Lab test results
 Direct shear test
Target dry unit weight (kN/m3)
Normal pressure (kPa)
19.5
80
150
300
17.5
80
150
300
14.8
20
40
80
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Lab test results
 Direct shear test
41
40
39
38
Peak Friction Angle (°)
37
36
35
34
33
32
31
Upstream
30
29
Midstream
28
Downstream
27
At 4% shear strain,
no peak resistance
26
25
14
15
16
17
Unit Weight
18
19
20
(kN/m 3 )
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Lab test results
 Revision of target density for triaxial tests
23
3.4
22
21
3.2
20
19
3.0
17
2.8
16
2.6
15
Specific Gravity
Unit weight (kN/m3)
18
14
13
12
11
Maximum dry unit weight from modified Proctor test
Target unit weight for roller compacted case (95% of modified Proctor)
Target unit weight for dozer compacted case (90% of modified Proctor)
Average dry unit weight measured at dozer compacted area
Minimum unit weight from lab test
Specific Gravity (secondary axis)
10
2.4
2.2
2.0
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Lab test results
 Consolidated undrained (CU) triaxial test
40
39
38
Friction Angle (°)
37
36
35
34
Upstream
33
Midstream
32
Downstream
31
30
14
15
16
17
Unit Weight
18
19
20
(kN/m 3 )
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Lab test results
 Scanning Electron Microscope (SEM) imaging
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Conclusion
 Hydraulic sorting (as a function of distance from the discharge point)





Increase of fines content
Decrease of specific gravity
Decrease of minimum density
Direct shear tests
peak friction angles vary from 33 to 40 degrees
 Consolidated Undrained (CU) triaxial tests

peak effective friction angle from 35 to 39 degrees
 Higher friction angles for the midstream and
downstream samples



Higher roughness
Better packing
Higher interlock forces
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Question?
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