Geosynthetic Mining Solutions at
Copper Tailings Dams: A Review of
the State of Practice in Chile.
Carlos Cacciuttolo, Engineering Council, Chile.
Jack Caldwell, Robertson GeoConsultants, Canada.
Scott Bernard, CICH AG, Chile.
Outline
• Introduction
• Use of Geosynthetics in Tailings Dams – Key Issues
• Seepage Control in Tailings Dams
• Geosynthetic Types used in Tailings Dams
• Constructability Issues on Tailings Dams
• Applications
• New Trends
• Conclusions
• Acknowledgments
Introduction
Introduction
Some copper-mining operations, which use flotation processes,
generate a total of approximately 100,000 mtpd of tailings that need
to be stored in a cost-effective, safe and environmentally friendly
manner.
This means tailing storage facilities (TSFs), which in some cases have a
100 m dam height that need to be designed for:
• Optimal containment;
• Preventing seepage from the impoundment through the dam and
adjacent areas, for environmental protection and dam safety;
• Controlling piping issues;
• Providing filter and drainage capacity; and
• Optimizing the physical and hydrologic stability of the TSF for the
mining lifetime (operation and closure), taking into account high
seismic activity and possible extreme floods.
Use of Geosynthetics in Tailings Dams
Key Issues
Use of Geosynthetics in Tailings Dams
Key Issues
Advantages
• No clay layers: geosynthetics offer an opportunity to minimize the use of costly clay filters for
grading the materials in the dam.
• Simplicity: geosynthetics simplify the construction process so that the overall construction
period is reduced.
• Effective long-term performance: geosynthetics offer better performance against acid-rock
drainage (ARD) generation—unlike impervious core dam materials (such as clay), whose
structural properties may change due to the effects of oxidization and leaching caused by
sulfide-rich mine tailings.
Disadvantages
•Prone to damage: geosynthetics are more susceptible to mechanical damage caused by by
settling of the support surface, differential deformations, or puncturing of the geomembrane.
• Geosynthetic loading: in order to design adequate geosynthetics systems, it is necessary to
consider water loading, excessive tailings loadings, or eventual loads of snow on
geomembranes placed on the upstream slope of the dam.
Sensitivity to climate conditions: extreme temperature changes cause geosynthetic thermal
contraction. Geosynthetics can be damaged by UV rays if they are permanently exposed to
them. The effect of wind on geosynthetics can also be critical.
Seepage Control in Tailings Dams
Seepage Control in Tailings Dams
• The deposition of slurry tailings from the dam crest
causes the development of beaches which typically
have the shape of a fan. The covering by the tailings
acts as a seal that eliminates or at least attenuates
seepage from eventual perforations or tears generated
during its useful life (Barrera and Lagas, 2012).
• In the case of tailings sand dams, slimes (cyclone
overflow) are discharged into the impoundment. These
materials are very fine (total tailings fine fraction) and
retain a great deal of water once deposited. This
results in higher water losses trapped in interstitial
slimes, with a very low permeability in the order of K ~
10-6 cm/s (Barrera, 1998).
•To prevent seepage through the dam foundation, a
cut-off trench and grout-curtain control system is
installed along the upstream toe of the dam, which
allows for the interception of the seepage. A
geotextile–geomembrane liner is placed at the
upstream face of the cut-off trench.
Source: Mafra et al., 2008.
Geosynthetic Types used in Tailings Dams
Geotextile and Geomembranes Types
used in Tailings Dams
Geotextiles
Table: Nonwoven, Needle-Punched Geotextile Properties
Properties of Material
Test Method
Unit of Measure
Required Value
Required Value
Weight per Area Unit
ASTM D5261
g/m2(oz/yd2)
≥ 335 (10)
≥ 180 (6)
Apparent Opening Size, Sieve No.
ASTM D4751
Mm
≤ 0.15
≤ 0.21
Grab Tensile Strength
ASTM D4632
N
≥ 1,110
≥ 600
Grab Elongation
ASTM D4632
%
≥ 50
≥ 50
Puncture Strength
ASTM D4833
N
≥ 665
≥ 350
Trapezoidal Tear
ASTM D4533
N
≥ 445
≥ 240
Permittivity
ASTM D4491
1/sec
≤ 1.2
≤ 1.4
Flow Rate
ASTM D4491
l/min/m2
≤ 3,100
≤ 4,500
UV Resistance (after 500 hours)
ASTM D4355
%
≥ 70
≥ 70
Geotextile and Geomembranes Types
used in Tailings Dams
Geomembranes
Table: HDPE Smooth-Texture, Black-Color Geomembrane Properties
Properties of Material
Test Method
Unit of Measure
Required Value
Thickness
ASTM D5199
mm (mil)
≥ 1.5 (60)
Density
ASTM D1505
g/cm3
≥ 0.94
Strength at Yield
ASTM D6693
N/mm
≥ 22
Strength at Break
ASTM D6693
N/mm
≥ 40
Elongation at Yield
ASTM D6693
%
≥ 12
Elongation at Break
ASTM D6693
%
≥ 700
Tear Resistance
ASTM D1004
N
≥ 186
Puncture Resistance
ASTM D4833
N
≥ 480
Oxidative Induction Time
ASTM D3895
Min
≥ 100
Carbon Black Content
ASTM D1603
%
2.0 – 3.0
Geotextile and Geomembranes Types
used in Tailings Dams
Geomembrane Design Matrix
Table: Geomembrane Liner Design Matrix (Lupo and Morrison, 2005)
Foundation
Conditions (α)
Liner
Bedding Soil (β)
Overliner Material
(γ)
Effective Normal Stress (MPa) (σ)
σ < 0.5
0.5< σ< 1.2
σ > 1.2
Coarse grained
Coarse grained Fine
grained
2.0 mm HDPE
2.0 mm HDPE
2.5 mm HDPE
1.5 mm HDPE
2.0 mm HDPE
2.5 mm HDPE
Fine grained
Coarse grained Fine
grained
1.5 mm HDPE
1.5 mm HDPE
2.0 mm HDPE
1.0 mm HDPE
1.5 mm HDPE
2.0 mm HDPE
Coarse grained
Coarse grained Fine
grained
2.0 mm LLDPE
2.0 mm LLDPE
2.5 mm LLDPE
1.5 mm LLDPE
2.0 mm LLDPE
2.5 mm LLDPE
Fine grained
Coarse grained Fine
grained
2.0 mm LLDPE
2.0 mm LLDPE
2.5 mm LLDPE
1.5 mm LLDPE
2.0 mm LLDPE
2.5 mm LLDPE
Firm or high stiffness
Soft or low stiffness
Constructability Issues on Tailings Dams
Constructability Issues on Tailings Dams
Climate and Topography Conditions
• Mine facilities in Chile are located
mainly in the Atacama Desert or the
Andes range areas, where the is an
adverse climate and extreme
topographic conditions.
• Construction of TSFs presents unique
challenges including demanding
construction schedules and difficulties in
sourcing specialized contractors.
• The geomembrane deployment
typically requires grading slopes not
higher than 2H:1V.
• Under windy conditions the use of
sand bags to secure the geomembrane
stability is necessary.
Source: Belfi, 2013; Incolur, 2013 webpage.
Constructability Issues on Tailings Dams
Geosynthetics Seam Works
• The geosynthetic sheets are unrolled
down the slope and cut to the
appropriate length to cover the entire
inclined slope.
• The panels are joined by manual
thermofusion weld seaming along the
slope,
• Panels are joined by manual extrusion
weld seaming along the length of the
dam.
• All welds and liners are inspected
using industry-accepted QA/QC controls
and test procedures.
• Workers, installers, and inspectors
must receive high-angle work and safety
training, which emphasizes the correct
use of anti-puncturing shoes, and
elements of personal safety for steepslope works.
Applications
Applications
Geosynthetics at Starter Dams Constructed with Borrow Materials
• The starter dam is the embankment of the TSF in the early stages, needs
to have a continuous impervious barrier along the upstream face of the
dam, as well as along the bottom of the dam (cut-off system), which
waterproofs the riverbed’s alluvium and the shoulders’ colluvium.
•An impervious core is installed on borrow
materials. This consists of a 1.5 mm (60
mill) flexible, HDPE geomembrane
bedding with two anti-puncture layers that
protect it against possible damage by the
construction materials: first a cushion layer
of nonwoven, needle-punched geotextile,
and second a silty sand layer are placed
as a filter core on the borrow material.
Source: Belfi and Incolour, 2013 webpage.
Applications
Geosynthetics at Cycloned Tailings Sand Dams
• The cycloned tailings sand dam typically has a crest width of 20 m, to provide: a safe base for
the wooden trestles (support of two tailings sand delivery pipelines); an adequate
geomembrane liner anchorage trench/slimes delivery pipeline space; electric lighting lines
space; and prompt access for adequate trafficability of vehicles maintenance/surveys.
• When a dam crest of 20 m and a 2H:1V upstream slope is constructed:
(1) a new wooden trestle lift of 5 m needs to be installed
along the dam crest and relocated to the tailings sand
pipelines;
(2) a slimes pipeline needs to be relocated; and
a new stage of nonwoven geotextile–HDPE geomembrane on
the upstream slope is required.
(3) Once the slimes pipeline have been relocated the
geosynthetic installer builds a new anchorage trench along
the tailings sand dam, starting the placing of the 200 g/m2 (6
oz/yd2) anti-puncture, nonwoven, needle-punched geotextile,
and once it is well advanced, placing the 1.5 mm (60 mill)
HDPE geomembrane.
Source: Barrientos, Tailings 2013 webpage.
(4) Finally the slimes spigot pipelines are installed.
Applications
Geosynthetics at Rockfill Dams
• Zoning within the waste rock dam section will need to be accomplished with the filter
criteria to avoid piping (Sherard, and Dunnigan 1985)., and can be achieved by varying
lift thickness and compaction specifications for different areas of the embankment.
• An impervious core of geosynthetic materials is installed on the upstream face of the
dam, consisting of 2 mm (80 mil) HDPE geomembrane cushioned by one 400 g/m2 (10
oz/yd2) anti-puncture, nonwoven geotextile that protects it against possible damage by
the dam materials
• Additionally, a nonwoven geotextile
sacrifice layer of 200 g/m2 (6 oz/yd2) is
placed over the HDPE geomembrane to
provide UV ray protection while the TSF is
filling with tailings
New Trends
Bituminous Geomembrane (BGM)
New Trends
Bituminous Geomembrane (BGM)
•A
bituminous geomembrane (BGM) liner is used
in projects worldwide, and shows the
waterproofing versatility of this type of
geomembrane in cases of earth dams with gentle
slopes, and concrete dams with subvertical slopes.
• The joints between the BGM panels ensure an
additional advantage over other types of
geomembranes. The joints are welded at a high
temperature created by a simple gas torch.
• This liner has advantages in terms of
withstanding wind effects, having no stringent
base layer requirement, being useable on other
dam types such as rolled compacted concrete
(RCC) dams, and decreasing construction times
and the quantity of borrow materials required.
Source: Coletanche webpage.
New Trends
Smart Geosynthetics
New Trends
Smart Geosynthetics
• A new emerging smart geosynthetic, fiber optics technology
(Dijcker et al., 2011), is used at TSFs to cushion the geomembrane
liners, monitor the dam’s behavior, and provide information.
• The new trends in future will be providing geosynthetic solutions
that will control and prevent the leakages at TSFs.
Source: Dijcker et al., 2011.
Conclusions
• Although the geomembrane is not completely waterproof,
it is nearly waterproof when compared to other materials
and some soils, even clay soils.
• The main function of geosynthetics on TSFs is to serve as
liner layer between different materials to prevent and
mitigate eventual leaks that may occur.
• The covering by the tailings acts as a seal that eliminates
or at least attenuates seepage derived from eventual
perforations or tears generated during its useful life.
• Use of geosynthetics at TSFs is growing daily, that support
environmentally friendly tailings-management solutions,
that control and reduce the tailings seepage, and decrease
the borrow pit works for filter dam construction.
Acknowledgments
The authors of this paper wish to express their
appreciation to the organizers of this important
conference for the invitation to participate and be part
of it, and also for having the opportunity to share
experiences with colleagues from around the world.
Carlos Cacciuttolo, Chile.
Jack Caldwell, Canada.
Scott Bernard, Chile.
[email protected]
[email protected]
[email protected]
Thank You for your Attention!
Thank you!