COVERS FOR MINE WASTE DISPOSAL FACILITIES By Andy Robertson and Shannon Shaw.
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Transcript of COVERS FOR MINE WASTE DISPOSAL FACILITIES By Andy Robertson and Shannon Shaw.
COVERS FOR
MINE WASTE DISPOSAL FACILITIES
By
Andy Robertson and Shannon Shaw
Review of Cover Purpose
• Access• Physical Isolation• Erosion Protection• Vegetation Establishment• Oxygen (oxidation) Control• Infiltration (leaching) Control
Soil Covers
• Types of Covers:
• Simple– Permeability depends on grain size– Compaction– Oxygen diffusion depends on moisture content
• Compound
• Complex– Variable– Multi-layered
waste
low density
high density
waste
moisture
Grey Eagle Tailings Cover
Trends in Cover Design
• Infiltration barrier design for wet climates (water barrier)• Evaporation enhancing designs for dry climates (water
balance/store and release)• Thick HDPE geomembrane covers to resist disruption
Typical comparison of alternative covers
A ) N o C o ve r
B ) M od erate Ve g etation C ove r
C ) G oo d Veg etation C o ve r
D ) L ow P erm ea bility Till S o il C o ve r
E ) H ig h P erm ea bility T ill S o il C o ve r
N o te : (“”) N u m b e rs are pe rce n t o f to ta lA n nu al precip ita tion
F a irG rass
G oodG rass
F a irG rass
F a irG rass
1 m
1 m
P rec ip ita tion E vapora tion R un o ff
S eepage
P rec ip ita tion E vapora tion R un o ff
R un o ff
S eepage
S eepage
Ta il ingsk= 6x10 cm /s-5
Ta il ingsk= 6x10 cm /s-5
Ta il ingsk= 6x10 cm /s
-5
P rec ip ita tion E vapora tion R un o ff
S eepage
k= 1x10 cm /s
T ill S o ilH igh P e rm eab ility
-4
Ta il ingsk= 6x10 cm /s
-5
Ta il ingsk= 6x10 cm /s
-5
P rec ip ita tion E vapora tion R un o ff
S eepage
k= 2x10 cm /s
T ill S o ilLow P e rm eab il ity
-6
Typical comparison of alternative covers
I) S o il B a rrier w ith S ynthe tic M em brane L iner,Lace ra l D ra in and S oil C over
H ) S o il B a rrier w ith La cera l D ra in and R ip rap C over
F ) R ip rap E rosion R esis tan t C ove r
G ) S oil B a rrie r w ith Lace ra l D ra in and S o il C ove r
0 .5 m
1 .0 m
0 .3 m
1 .0 m
P rec ip ita tion E vapo ra tion R un o ff
S eepage
P rec ip ita tion E vapo ra tion R un o ff
S eepage
La te ra l D ra inS lope0 .5%
Ta il ingsk= 6x10 cm /s
-5
P rec ip ita tion E vapo ra tion R un o ff
S eepage
k= 1x10 cm /s C ov e r S o il-4
P rec ip ita tion E vapo ra tion R un o ff
S eepage
k= 1x10 cm /s B a rrie r S o il-7L inea r
S lope0 .5%
0 .3 m
0 .6 m
1 .0 m
F a irG rass
S lope0 .5%
0 .3 m
1 .0 m
1 .0 m
F a irG rass
La te ra l D ra in
La te ra l D ra in
k= 5x10 cm /s-3
Ta il ingsk= 6x10 cm /s
-5
k= 1x10 cm /s R oc k/G rave l-2
k= 1x10 cm /s B a rrie r S o il-7
k= 5x10 cm /s-3
k= 1x10 cm /s C ov e r S o il-1
k= 1x10 cm /s B a rrie r S o il-7
k= 5x10 cm /s-3
Ta il ingsk= 6x10 cm /s
-5
Ta il ingsk= 6x10 cm /s
-5
k= 1x10 cm /s R oc k/G rave l-2
N o te : (“”) N um b ers are pe rcen t o f to ta lA nnual precip itat ion
mm
Dry Cover Costs
• Oxygen Control• Migration Control
• Simple Covers– Soil covers
• Complex Covers– Multiple soil– “Cefyl”– Clay layered– Geomembrane*
* Perpetual replacement @ 50 year intervals ~22% of present value hence long term fund $0.40-0.60/tonne
$2 - $6/m2
or $0.03-0.10/tonne waste rock
$20 - $30/m2
Or $0.33-0.50/tonne waste rock
Water Cover Costs
• New Rock Waste– In natural water bodies
• Haulage costs– In man-made impoundments
• $0.25 - $1.50 + haulage costs
• Old Rock Waste– With treatment of storage products– >$2.75 - $4.00/tonne
Suitability of Cover Types
Tailings Waste RockPotential Problems
Risk inDesign
Risk duringConstruction(slimes)
Long-termRisk ofDisruption
Risk inDesign
Risk duringConstruction(slopes)
Long-termRisk ofDisruption
Access
Slumping
Erosion Sheet
Channel
Consolidation
Biota
Infiltration
Oxygen Flux
High Risk Elements of Cover Performance
Minimizing Risk of Cover Failure1. Materials
– Maximize use of natural, durable materials– Minimize use of geosynthetics which deteriorate– Rip-rap control of erosion in dry climates
2. Climate• In dry climates:
– consider evaporative cover designs– increase use of rip-rap for erosion protection– provide for sedimentation control
• In wet climates:– consider infiltration cover designs– consider water covers
Minimizing Risk of Cover Failure
3. Biota– Beaver (beaver control or wide channels)– Burrowing animals (bio-intrusion layers)– Ants & insects (bio-intrusion layers)– Anthropogenic activity (institutional control)– Roots (control vegetation species)
4. Monitoring & Maintenance– Erosion– Settlement– Sedimentation (& Glaciation)– Biotic factors (fauna, flora, man)