CIM AGM- Edmonton, Alberta
PERFORMANCE OF COMPOSITE PASTE
FILL FENCES
Presented by:
Paul Hughes
Authored by:
Paul Hughes,
Dr. Rimas Pakalnis,
Dr. Michael Hitch,
Cristian Caceres
University of British Columbia
Ray Wilkins
Goldcorp Inc – Red Lake Mine
Purpose of Research
• What are the loading mechanics of
paste against barricades?
• What is the capacity of the composite
paste fill fences?
• Based on the loading mechanics of the
paste, do the fill fences pose a risk of
failure?
Outline
•
•
•
•
•
•
•
•
•
Glossary of Terms
General Introduction
Research Methodology
Site Description
Instrumentation Program
Results
Analysis
Conclusions
Recommendation for
Future Work
Glossary of Terms:
PASTE
Potvin, Thomas, Fourie (2005),
define paste as follows:
• Contains at least 15% passing
20 microns
• When placed does not bleed
water
• Does not settle or segregate in
a pipeline
• Has a slump less than 230 mm
• Contains typically between
75% and 85% solid by weight
• Between 1% and 10% Binder
Glossary of Terms:
COMPOSITE PASTE
BARRICADE
•A paste barricade, or paste fill
fence, is a constructed barricade
whose purpose is to retain
backfill within a mined-out
stope.
•Composite Fill Fence :
– rebar skeleton
– adequate thickness of
shotcrete
•Other examples:
– Concrete bulkheads
– Timber bulkheads
– Cable sling bulkheads
Why is This Research Necessary?
• The majority of the applicable barricade research
focuses on hydraulic fill barricades in open stope
mining.
• Barricade pressures in these instances are much
larger than those experienced in paste backfill
barricades.
• Current paste loading theory is based on material
with a different loading mechanism.
• Although some research is currently underway, the
majority of the paste barricade research is based on
brick barricades and not composite barricade types.
Contributions to Operations
• Economic benefits:
» increases in fill pour rate
» continuous paste pours
» widening of stope dimensions dictated by barricade
loads.
• Safety benefits:
» discontinuities between successive paste pours
would be minimized
» the risk of designing a backfill stope that would
exceed a barricade’s capacity is largely eliminated.
SITE STUDY- Red Lake Mine
RED
LAKE
•Located in
Balmertown, Ontario
•Nearest towns:
Kenora and Dryden
•Accessed via Highway
105 or local airport
•Nearest International
Airport - Winnipeg,
Manitoba
Red Lake Mining Methods
Mining
Method
2002
2003
2004
Overhand
Cut and Fill
100%
70%
60%
Underhand
Cut and Fill
0%
25%
25%
Pillar
Recovery
0%
5%
15%
Underhand
Cut
Overhand
Pillar Removal
Cut and
and Fill
Fill
Progression
of mining
Fill Fences at Red Lake
•
•
•
•
Rebar anchored 0.6 m on walls and floor when
Holes in rock must be filled with resin and 2.1 m ,#6 rebar must be spun into hole
Fence to be constructed with #6 rebar on a 0.6 m by 0.6 m grid
Rebar connections must overlap a minimum of 45 cm Secure ‘bed springs’ with tie
wraps inside of fence designed height
• Apply minimum of 10 cm of shotcrete
• Allow shotcrete to cure for twenty four hours prior to placement of paste
• If necessary, 10 cm paste pipe to be installed through fence to provide an outlet for
the paste line flush
Paste Practices
•The paste recipe at Red Lake is between 510% cement by dry weight
•UCS of 2MPa
• Stopes are prepared with paste barricade
and prep of engineered floor for UCF stopes
•Mixed on surface and pumped through a
gravity fed system
•The total length of the paste system is
2500m
• Average velocities are 1.83m/s (Mah, 2003)
•Batch plant can produce 80 tonnes per hour
of paste
•Achievable pouring rate at the stope is
40m3/hr.
Fill Fence Inventory
Instruments
Fill Fence
Earth Pressure
Shotcrete
Cells
Strain Gauges
Rebar
Strain
Gauges
Measured Fill
Height
32-826-8
5
0
0
No
37-746-2
1
1
0
No
34-806-4
2
2
0
No
31-806-3
1
1
0
Estimated
36-746-1
2
2
0
Estimated
34-806-1
1
1
0
Estimated
34-786-14a
2
3
3
Direct
34-786-14b
2
3
3
Direct
Destructive
Test
2
3
3
N/A
Instruments Used in Monitoring
Rebar Strain Gauges
Concrete Strain Gauges
Earth Pressure Cell
Load Cell
Tiltmeters
Typical Fence Layout
3.5m
EPC 2
1.7 m
SG3
1.2m
SG2
Rebar
SG1
SG1
0.6m
EPC 1
1.8 m
Rebar SG2
Not to Scale
3.85m
Tilt meters
Destructive Fill Fence Test
8m
1
2.6m
4m
2
3
7
8
2.5 m
1.5 m
6
2m
5 a,b,c
2.75 m
4
1
Vert. Rebar SG
5 (a) Vert Left SG (b) Load Cell (c) Vert Right SG
2
Horiz. Top SG
6
Horiz. Bottom Rebar SG
3
Horiz. Top Rebar SG
7
EPC Bottom Right
8
1 m x 1m Loading Plate
4
EPC Top Left
Not to Scale
Typical Pressure and Strain Plots
0.0300
125
2.5
100
2
4
0.0275
0.0250
0.0200
2.5
2
0.0150
0.0125
1.5
Fill Height (m)
0.0175
Strain [uE]
0.0225
Pressure (MPa)
75
1.5
50
1
25
0.5
3
0
9-Jul-04
9-Jul-04
10-Jul-04
10-Jul-04
11-Jul-04
11-Jul-04
12-Jul-04
12-Jul-04
13-Jul-04
13-Jul-04
0
14-Jul-04
0.0100
0.0075
0.0050
1
-25
-0.5
0.5
-50
-1
0.0025
0
0.0000
-75
-1.5
Date
-0.0025
02-Aug-04
-0.5
04-Aug-04
06-Aug-04
08-Aug-04
10-Aug-04
12-Aug-04
SG1
SG2
SG3
Date
EPC 1
EPC 2
FILL HEIGHT
Pressure Plot for 36-746-1
• Spikes occur during paste line flush
Strain Plot for 31-806-3
• Strains correspond to paste height
• Maximum Pressure 0.025 MPa
• Maximum strain recorded 125
microstrain
Applied Stress Within Shotcrete (MPa)
3.5
Summary of Results
Fence
32-826-8
37-746-2
34-806-4
31-806-3
36-746-1
34-806-1
34-786-14a
34-786-14b
Destructive Test
Height
(m)
4.50
3.90
3.60
4.25
5.25
3.70
3.40
3.85
2.60
Maximum Maximum
Maximum Strain in Strain in
Width
Pressure Concrete
Rebar
(m)
(kPa)
(με)
(με)
N/A
50
N/A
N/A
3.60
N/A
N/A
N/A
5.35
22.5
2000
N/A
4.25
20
125
N/A
12.25
25
-220
N/A
6.90
40
-375
N/A
4.80
14
35
25
3.50
19
180
130
8.00
127
-50
1100
Paste Loading Mechanism
•
•
The ratio of assumed vertical load vs. measured horizontal loads was
investigated and the paste was considered a Rankine Soil during this
loading .
The Rankine Theory provides the following formula to estimate the
active lateral earth Pressure:
σh= Ka σv
Where:
σv=γ H
Ka = (1- sin Φ)/ (1+ sin Φ)
γ= unit weigh of soil (18.63kN)
H = height of soil (m)
•
•
To determine the friction angle of the paste- needed an actual or
inferred height paste and recorded earth pressure cells.
Heights and pressures could be compared to determine if the expected
Rankine linear relationship exists between these two measurements.
Paste Loading Mechanism
40.00
35.00
Lateral Earth Pressure (kPa)
30.00
General linear trend between
lateral earth pressure and fill
height
Ka= 1
Slope of line relates to coefficent of lateral earth
pressures
y = 9.3778x
R2 = 0.7999
25.00
20.00
High R-squared value,
indicates relationship is not
dependant on fill rate or
cement content
15.00
10.00
5.00
0.00
0.00
0.50
1.00
1.50
2.00
2.50
3.00
3.50
Fill Height (m)
36-746-1 (Elev 0.55m)
36-746-1 (Elev. 2.6m)
34-786-14a (Elev 0.6m)
34-806-1 (Elev 0.60m)
31-806-3 (Elev 0.8m)
4.00
Fill Fence32-826-8
Fence had horizontal and vertical EPC installed together
Ka = 1
Rankine
Theory states that Ka = σh/ σv
0.0800
General linear agreement between
horziontal stress and horizontal
stresses.
0.0700
Horizontal Load (MPa)
0.0600
Slope of line represents co-efficent
of lateral earth pressure
y = 0.5477x
R2 = 0.9167
0.0500
0.0400
0.0300
0.0200
0.0100
0.0000
0
0.01
0.02
0.03
0.04
0.05
Vertical Load (MPa)
0.06
0.07
0.08
0.09
0.1
Determine Coefficient of Lateral Earth Pressure
• Using Rankine Theory :
– σh= Ka γ H
• Solve for Ka
Instrument
Height
Friction
Fill Fence
(m)
Ka Value Angle
0.55
0.46
21.9
36-746-1
2.6
0.69
10.4
34-806-1
0.6
0.63
13.0
34-786-14a
0.6
0.57
15.9
31-806-3
0.8
0.43
23.8
32-826-8
0.25
0.55
16.9
Average
0.56
16.99
Effect of Fill Rate on Friction Angle
30.0
Poor agreement between fill rate
and friction angle. Slope of
trend line is near horizontal
indicating that friction angle is
not related to fill rate.
25.0
Friction Angle
20.0
15.0
R2 = 0.024
10.0
5.0
0.0
0.00
0.05
0.10
0.15
0.20
0.25
Fill Rate (m/hr)
36-746-1
34-806-1
34-786-14a
31-806-3
0.30
0.35
0.40
Stress vs. Strain Relationship
•
•
The stress-strain behavior analysis of the fence determines if the fence
undergoes any plastic strain during imposed loads.
Fence can no longer take imposed loads and ultimately will fail.
•
Following Fences with known fill height were used:
–
–
–
–
–
•
31-806-3
36-746-1
34-806-1
34-786-14a
Destructive Test
Assumptions:
–
the strain in the strain gauge is directly related to the imposed load of the
fence
– was poured at a constant rate and the fill rate is based on the total height of
the paste divided by the time taken to fill the stope.
Typical Stress vs. Strain Plot
25.000
20.000
Stress (kPa)
15.000
10.000
5.000
-150.000
-100.000
-50.000
0.000
0.000
50.000
Strain (uE)
SG1
SG2
SG3
100.000
150.000
Destructive Fill Fence Stress vs. Strain Plot
120.00
110.00
100.00
100 kPa
90.00
Yielding occurs in rebar at approximately
100 kPa
Load (kPa)
80.00
70.00
Shotcrete trends do not show yielding
60.00
Performance below 100kPa is linear
indicating an elastic behavior
50.00
40.00
Failure deemed to occur at 100 kPa for fill
fences
30.00
Note: High level of recorded strains not
recorded on any other fence
20.00
10.00
0.00
-25
25
75
125
175
225
275
325
375
425
475
525
575
625
675
725
775
825
875
925
975 1025 1075 1125 1175
Strain (Microstrain)
Vertical
Horizontal Top
Horizontal Bottom
Vertical Left
Vertical Right
Horizontal Top
Horizontal Bottom
'Converted Data'!$P$6
All Stress vs. Strain Plots
120.00
110.00
100.00
100 kPa: yielding of fence
90.00
80.00
Load (kPa)
70.00
60.00
50.00
40.00
30.00
Below 40 kPa: recorded stress
and strain within instrumented
paste pour fences
20.00
10.00
0.00
1200
34-786-14a Shotcrete SGs
1100
36-746-1 SGs
1000
34-806-1 SGs
900
34-786-14a Rebar SGs
800
Strain (Microstrain)
Destructive Test Shotcrete SGs 31-806-3 SGs
700
600
500
400
300
200
100
0
-100
-200
-300
Destructive Test Rebar SGs
Conclusions
At the outset of this thesis, three questions
needed to be addressed:
• What are the loading mechanisms of paste against
barricades?
• What is the capacity of the paste fill fences at Red
Lake?
• Based on the loading mechanism of the paste, do the
fill fences pose a risk of failure?
What are the loading mechanisms of paste?
40.00
30.00
Lateral Earth Pressure (kPa)
•Rankine soil like
behavior
•Coefficient of lateral
earth pressure, Ka,
was 0.56
•Loading rate had no
effect on value of Ka
35.00
General linear trend between
lateral earth pressure and fill
height
Slope of line relates to coefficent of lateral earth
pressures
y = 9.3778x
R2 = 0.7999
25.00
20.00
High R-squared value,
indicates relationship is not
dependant on fill rate or
cement content
15.00
10.00
5.00
0.00
0.00
0.50
1.00
1.50
2.00
2.50
3.00
3.50
4.00
Fill Height (m)
36-746-1 (Elev 0.55m)
36-746-1 (Elev. 2.6m)
34-786-14a (Elev 0.6m)
34-806-1 (Elev 0.60m)
31-806-3 (Elev 0.8m)
30.0
Poor agreement between fill rate
and friction angle. Slope of
trend line is near horizontal
indicating that friction angle is
not related to fill rate.
25.0
Friction Angle
20.0
Instrument
Height
Friction
Fill Fence
(m)
Ka Value Angle
0.55
0.46
21.9
36-746-1
2.6
0.69
10.4
34-806-1
0.6
0.63
13.0
34-786-14a
0.6
0.57
15.9
31-806-3
0.8
0.43
23.8
32-826-8
0.25
0.55
16.9
Average
0.56
16.99
15.0
R2 = 0.024
10.0
5.0
0.0
0.00
0.05
0.10
0.15
0.20
0.25
Fill Rate (m/hr)
36-746-1
34-806-1
34-786-14a
31-806-3
0.30
0.35
0.40
What is the capacity of the paste fill fences?
120.00
110.00
100.00
100 kPa
90.00
Yielding occurs in rebar at approximately
100 kPa
Load (kPa)
80.00
70.00
Shotcrete trends do not show yielding
60.00
Performance below 100kPa is linear
indicating an elastic behavior
50.00
40.00
Failure deemed to occur at 100 kPa for fill
fences
30.00
Note: High level of recorded strains not
recorded on any other fence
20.00
10.00
0.00
-25
25
75
125
175
225
275
325
375
425
475
525
575
625
675
725
775
825
875
925
975 1025 1075 1125 1175
Strain (Microstrain)
Vertical
Horizontal Top
Horizontal Bottom
Vertical Left
Vertical Right
Horizontal Top
Horizontal Bottom
'Converted Data'!$P$6
Based on the loading mechanism of the paste, do the fill
fences pose a risk of failure?
120.00
110.00
100.00
Height
Fence
(m)
80.00
32-826-8
4.50
70.00
37-746-2
3.90
60.00
34-806-4
3.60
31-806-3
4.25
50.00
36-746-1
5.25
40.00
34-806-1
3.70
30.00
34-786-14a
3.40
34-786-14b 20.00
3.85
Destructive Test 10.00
2.60
Width
(m)
N/A
3.60
5.35
4.25
12.25
6.90
4.80
3.50
8.00
Load (kPa)
90.00
Maximum Maximum
Maximum Strain in Strain in
100 kPa:
yielding of fence
Pressure
Concrete
Rebar
(kPa)
(με)
(με)
50
N/A
N/A
N/A
N/A
N/A
22.5
2000
N/A
20
125
N/A
25
-220
N/A
40
-375
N/A
Below 40 kPa: 35
recorded stress
14
25
and strain within instrumented
19
180
130
paste pour fences
127
-50
1100
0.00
1200
34-786-14a Shotcrete SGs
1100
36-746-1 SGs
1000
34-806-1 SGs
900
34-786-14a Rebar SGs
800
Strain (Microstrain)
Destructive Test Shotcrete SGs 31-806-3 SGs
700
600
500
400
300
200
100
0
-100
-200
-300
Destructive Test Rebar SGs
Conclusions
From this research, the following recommendations were made to
Red Lake Mine:
– Fill pressures during backfill do not differ based on fill rate;
– Fill fence construction is suitable to the applied loads measured
during the testing;
– No alterations to fence construction are necessary;
– Maximum pressures were recorded during paste line flushes;
– In order to reduce loads on fence, line flushes should be done
outside of the backfilled stopes;
– Continuous pouring is advised for underhand cut and fill stopes as it
will eliminate hazards associated with ground fall due to cold joints.
Recommendations are currently being applied at Red Lake Mine.
Recommendation for Future Work
• Testing of other types of barricades
• Testing should be carried out to determine the
benefits of tying in the back and the floor to the fill
fence with embedded rebar.
• In addition to fence construction, monitoring of paste
pours should be carried out to determine the relation
of the percentage of cement within the paste and the
loading rate of placement to the coefficient of lateral
earth pressure.
• A more complex numerical model is necessary to
develop an understanding of the interaction between
the rebar and shotcrete under the paste loads.
Acknowledgements
• Goldcorp Ltd.’s Red Lake Mine
• NSERC IPS Program
• The trusts of the William Alexander Mackenzie
Scholarship and the Dr F J Nicholson Scholarship.
• Rocscience for providing software that was essential
in my research.S
• Josh Clelland, Ali Rana and Kathryn Dehn.
• Workforce at Red Lake mine for their assistance
throughout. I would like specifically to thank Grant
Corey, Boi Linh Van, Danielle Pelletier and Ray
Wilkins
• Dr. Rimas Pakalnis
• Yieldpoint for assistance and instrumentation