6-Landfill Liners-14s - 2 Slides Per Page
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Transcript of 6-Landfill Liners-14s - 2 Slides Per Page
1
Landfill Settlement and Liners
A/Prof Hadi Khabbaz
Email: [email protected]
Applied
Geotechnics
Solid Wastes
2
Geotechnical Aspects of
Landfills
• Landfill Stability
• Landfill Settlement
• Landfill Liners
3
Potential landfill infrastructure failure
modes: stability and integrity (Dixon and Jones, 2005)
Potential landfill infrastructure failure
modes: stability and integrity (Dixon and Jones, 2005)
4
Potential landfill infrastructure failure
modes: stability and integrity (Dixon and Jones, 2005)
Potential landfill infrastructure failure
modes: stability and integrity (Dixon and Jones, 2005)
5
Potential landfill infrastructure failure
modes: stability and integrity (Dixon and Jones, 2005)
Potential landfill infrastructure failure
modes: stability and integrity (Dixon and Jones, 2005)
6
Potential landfill infrastructure failure
modes: stability and integrity (Dixon and Jones, 2005)
• Landfill Settlement
• Compacted Clay Liners (CCLs)
– Compaction
– Clay Mineralogy
• Geosynthetic Clay Liners (GCLs)
OUTLINE
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Landfill
Settlement
Settlement occurs during filling stage and continues over
an extended period.
Landfill settlement is mostly due to compression of wastes.
Final settlement can be as large as 30% of the initial fill
height.
Early settlement during filling stage is desirable.
A large post-closure settlement is undesirable. Surface ponding and crakes in cover soil
Damage to geomembrane and leachate collection system
Settlement of foundation soil may be significant if landfill is
located on soft ground.
Settlement
8
The settlement of landfill affects:
The design of protection systems (covers, barriers
and drains)
Storage capacity
Cost and feasibility of using the underlying refuse for
the support of buildings, pavements and utilities.
Mechanism of Solid Waste Settlement
Excessive settlements Cause fracture of covers & drains
Increase moisture into the landfill Produce more leachate
Complexity of Solid Waste Settlement
The mechanisms of refuse settlement are complex.
1. Extreme heterogeneity of waste fill
2. Presence of large voids
3. Chemical reactions (corrosion, oxidation and
combustion)
4. Biological degradation (fermentation and decay)
Why?
9
Factors Affecting the Magnitude of Settlement
1. Waste compaction effort and placement sequence
2. Content of the decomposable materials
3. Overburden pressure and stress history (vertical
expansion over an old landfill
4. Leachate level and fluctuation in the landfill
5. Landfill operation methods (e.g. leachate recirculation
accelerates biodegradation)
6. Environmental factors (e.g. moisture content,
temperature and gases present )
Estimation of Landfill Settlement
The settlement of MSW includes primary consolidation and
long-term secondary compression (creep).
HHH c
H = total settlement of solid waste
Hc = primary settlement of solid waste
H = long-term secondary settlement of solid waste
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o
o
c He1
eHS
• How can e be estimated?
It is different for soils under various loading
conditions
It can be simulated in the lab using
Oedometer test.
Primary Settlement
Solid waste behaviour depends upon previous loading history.
Pressure (kPa)
e
pc
log scale
e1
e2
)'
''log(Ce
2
22c2
)'
''log(Ce
1
11r1
1
1
2
2
Primary Settlement
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Settlement
o
o
f
o
c
tf H)log(e1
CS
fopcif
Settlement
o
o
f
o
rtf H)(log
e1
CS
pcfoif
of
Primary Settlement
Settlement
o
pc
f
o
c
o
o
pc
o
rtf H)(log
e1
CH)(log
e1
CS
fpcoif
Primary Settlement
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In 1-D Consolidation assume the
soil is fully saturated:
Sr = 1 then:
eo = Gs . wo Sr . e = Gs . w
What is the value of Gs?
Primary Settlement
NOTE: Gs, Cc and Cr are not constant for
MSW.
Secondary Settlement (Creep)
o
1
2
1
H)t
t(log
e1
CH
H = long-term secondary settlement
e1 = void ratio of the waste layer at the end of primary consolidation
Ho = initial thickness of the waste layer before settlement
C = secondary compression index
t1 = starting time of the time period for which long-term settlement of
the layer is desired (e.g. t1 = 1 month)
t2 = ending time of the time period for which long-term settlement of the
layer is desired
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Example
Time period Height of solid waste filled
feet metre
1st month 12 3.6
2nd month 18 5.4
3rd month 16 4.8
4th month 10 3.0
5th month 14 4.2
The filling procedure of a new municipal solid waste landfill is listed
below. Calculate the total settlement at the end of the 5th month.
gwaste = 70 lb/ft3 (11 kN/m3)
o = 1000 lb/ft2 (48 kPa)
t1 = 1 month
Cc= Cc/(1+eo) = 0.26
C= C/(1+e1) = 0.07
H0 = 70 ft (21.34m)
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Example (Solution)
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27
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First layer
Second layer
Third layer
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Fourth layer
Fifth layer
2.51/21.34 = 0.118 or 11.8%
Compacted
Clay Liners
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Compacted Clay Liners
Compacted clay soil is widely used
1. to line landfills and waste impoundments,
2. to cap new waste disposal units, and
3. to close old waste disposal sites.
Compacted clay liners and covers should have a
permeability coefficient less than or equal to a
specified maximum value. (k = 1.010-9 m/s)
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Compacted Clay Liners (CCLs)
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www.abgltd.com/Erosamat%20type%203.asp
34 http://www.caawsystems.com/products/images/Geonet%20(3).JPG
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36
Geomembrane Liners (GLs)
Seam lengths should be monitored carefully
www.ettlinc.com/Ldfl%20CQC-CQA%20Services.HTM
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Clay Liner
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Comparison between Geotechnical Compacted Clay
and Landfill Compacted Clay Liners
Design Criteria:
Geotechnical Compacted
Clay
Design Criteria:
Landfill Compacted Clay
Bearing capacity (shear
strength); compressibility
Permeability, shear
strength, shrinkage
potential, chemical
resistance and compatibility
Construction
Requirement:
Construction
Requirement:
90 to 100% of maximum dry
density (both sides of
optimum water content)
90 to 100% of maximum dry
density (wet side of
optimum water content)
Lift thickness is generally
250 to 450 mm.
Lift thickness is not more
than 150 mm after
compaction
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Quiz
Many deposits of clayey soil (e.g. glacially deposited
materials) are mixed with gravel.
According to laboratory testing results it is possible to
achieve a hydraulic conductivity less than 110-9 m/s
using a soil with up to 50% gravel. Do you think this
soil can be used directly in field construction
specifications for a clay liner? Why or why not?
Isolated pockets of segregated gravel particles, whose voids
are not filled with clayey material would tend to increase the
overall hydraulic conductivity of the clay liner.
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Clay Liner Blowout
Empty landfill, with liner, below the water table
dL
dcKh
w
s
2
bw
ubb
g
g
g
Critical Hydraulic Head for Liner Base
hb = critical head (relative to landfill base elevation, m)
Kb = empirical constant ≅ 1/3
gw = unit weight of water (kN/m3)
gs = unit weight of soil (kN/m3)
cu = undrained shear strength of clay (kPa)
d = liner thickness (m)
Lb = length of base of landfill (m)
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Example
An empty landfill with a clay liner is shown in the figure.
The thickness of the liner, d, is 800 mm. The undrained
cohesion of clay is 100 kPa and its density is 1.8 t/m3.
Find the factor of safety of this clay liner against blowout.
2m
2.8m
2.5m
hb = 1.36 + 1.44 = 2.8 m > 2 m OK
Compaction and Permeability Consideration
One of the most important aspects of construction to
have low hydraulic conductivity is proper remoulding
and compaction of the soil.
Important tests are:
1. Compaction Test
2. Permeability Test
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Compaction and Permeability Consideration
Compaction Test Permeability Test
From Das, 2001
Permeability Tests
Constant Head Falling Head
Aht
qLK
2
1
h
hln
At
aLK
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Compaction
Uncontrolled Landfill
(No controlled placement
and no compaction)
1m
Variable
1m
Controlled Sanitary
Landfill
(Spread and compacted
in layers of 2-3m thick;
encapsulated with soil
in cells of 2-6m thick)
25
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Compaction
Definition: Mechanical densification of soil is
called compaction. It involves expulsion of air
from void spaces of a soil.
Application: compaction is very important
when soil is used as construction materials.
Advantages:
Reduce compressibility
Increase strength
Reduce permeability
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Factors Affecting Compaction
Compactive effort (compaction energy)
Water (moisture) content
Soil type
Initial density (void ratio)
Number of passes of rolling equipment
Frequency and amplitude of loading equipment
Number of drops of a falling hammer
Weight and height of drop of hammer
Field
Lab
Compaction energy is a function of:
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51 http://geotech.uta.edu/lab/Main/SandCone/index.htm
Compaction Mould in the Lab
Volume ≈ 1000 cm3
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Compaction Hammer in the Lab
http://www.controls.it/immagini/product_zoom/33_EN_Compaction_new.jpg http://www.eleusa.com/pdf/Soil/compaction.pdf
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53 http://www.eleusa.com/pdf/Soil/compaction.pdf
Compaction Hammer
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Sample Ejector
http://www.eleusa.com/pdf/Soil/compaction.pdf
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Compaction Standard Test Proctor (1930)
Proctor Introduced dry density as a measure of
compaction.
The water content of the soil is very likely to vary
from time to time, hence the field total unit weight.
Therefore, the dry unit weight of the soil is always
used as a means of reporting the test results and
eventually applying in real applications.
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Compaction Standard Test Proctor (1930)
Compaction: Standard
Mass of hammer 2.7 kg
Height of hammer fall 300 mm
No. of Layers 3
No. of blows per layer 25
Compaction energy* 595.5 kJ/m3
AS 1289
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Compaction Standard Test Proctor (1930)
Compaction: Standard Modified
Mass of hammer 2.7 kg 4.9 kg
Height of hammer fall 300 mm 450 mm
No. of Layers 3 5
No. of blows per layer 25 25
Compaction energy* 595.5 kJ/m3 2701 kJ/m3
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Compaction Energy
E = mgh (J)
E1 = 2.79.80.3 = 7.94 J
Et = (7.35 J) (3 layers) (25 blows) = 595.5 J
Es = 595.5 J / 1000 cm3 = 595.5 kJ/m3
Vol.≈1000 cc
Standard Compaction:
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59 Water Content (%)
Dry
Un
it W
eig
ht
(kN
/m3)
Compaction Curve
MDD = 2.28 t/m3
OMC = 6.8%
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Effect of Compaction on Soil Structure
Max. dry
density
Optimum
water
content
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Effect of Compaction on Soil Structure
Wet side of
compaction
Dry side of
compaction
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Pe
rme
ab
ilit
y c
m/s
) D
ry D
en
sit
y
Moisture Content (%)
Change in
Permeability Wet Side of the
Optimum Water
Content
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63
Field Density
1. Sand Replacement
2. Water or Oil Replacement (Balloon test)
3. Core Recovery Method (for cohesive soils)
4. Nuclear Density Meter
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Field Density (1)
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65 http://geotech.uta.edu/lab/Main/SandCone/index.htm
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34
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68
35
69
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Field Density: Water replacement
Check valve
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Field Density: Balloon Test Device
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Field Density: Oil Replacement
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Lift Height
450 mm
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Relative Compaction (RC)
100Density Lab Max.
Density FieldCompactionlativeRe
100RCmax(Lab)d,
)field(d
g
g
Can Relative Compaction be greater than 100%?
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75
Saturated Line (Zero Air Voids)
Zero
Air
Voids
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Useful Relationships
eSwG rs
Zero Air Voids
Dry Density
w1
wetdry
e1
G wsdry
S
wszav
wG1
.G
Dry Density
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Tamping Foot Rollers (Mesh, Grid)
Sheep’s-foot Rollers for clay
High contact pressures 1400 - 1700 kPa
Several parallel rollers can be towed
Suitable for cohesive soils
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Example
For a clayey soil used as liner material, the Modified
Proctor Test results were:
3
maxd m/kN2.18)( g
%14wopt
7.2Gs
Determine the value of the degree of saturation at the
maximum dry density.
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Example (Solution)
3
maxd m/kN2.18)( g %14wopt 7.2Gs
1G
11v
ve
d
ws
d
s
s
t g
g
g
g
Given:
454.012.18
8.97.2e
eSwG rs 454.0
147.2
e
wGS s
r
%26.83Sr
%83Sr
Dynamic Compaction
Dynamic compaction involves dropping a heavy mass
(M) from a certain height (H) several times in one
place. The process is repeated on a grid pattern
across the site.
H
M
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Trials indicate that the masses in the range
of 5 to 20 tonnes and drops in the range of 5
to 20 m are effective for compacting loose
sandy soils and MSW but not clayey soils.
Dynamic Compaction
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Compaction Pattern
http://www.iaeg.info/iaeg2006/PAPERS/IAEG_294.PDF
Maximum Depth
HMdmax
dmax = the maximum depth of influence (m)
H = the average drop height (m)
M = the mass of the pounder (t)
= 0.3 to 0.6 (depends on the site properties)
0.6
0.35
0.5
Silty sand
Municipal waste
Clayey sand
0.3 - 0.4
0.4 -0.5
Silt with low Sr
Silt with high Sr
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Quiz
The dynamic compaction method is applied on a closed
municipal solid waste landfill site. The mass of the pounder
is 10 tonnes and the average drop height is 8 m.
(a) Determine the maximum depth of influence for this
dynamic compaction.
(b) If the required influence depth is 4 m, calculate the
drop height if the same pounder is employed.
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87
Recap for Compaction
Standard and Conventional Compaction
optimum moisture content (OMC)
maximum dry density (MDD)
dry side and wet side of OMC
Dynamic Compaction
(is an effective and economical alternative
to conventional compaction)
Clay
Mineralogy
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CLAY MINERALOGY
1. Clays play a primary role in reducing hydraulic
conductivity of soils used in the construction of
liners and slurry walls for contaminant of waste
disposal facilities
2. Clay minerals have a crystalline structure, an
equivalent diameter of less than 2 mm. Its
permeability coefficient is very low (10-8 - 10-12 m/s).
0.2 0.6 6 20
2mm 0.002mm 0.060mm 60mm 200mm
3. Clay particles are generally flaky (plate-like in
shape) but some are tubular
Shape of Clay Particles
4. Their thickness is very small relative to their length
& breadth, in some cases as thin as 1/100 of the
length
Flocculated
Structure
(edge-to-face
or edge-to-
edge)
Dispersed
Structure
(face-to-face
orientation)
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Specific Surface
Clays have a large surface area with a high percent of
constituting molecules distributed on the surface and
carry a net negative charge. This charge attract the
positive end of water molecules. Thus a lot of water
may be held as adsorbed water within a clay mass.
The specific surface is defined as the surface area (m2)
per gram of mass.
It ranges from: 5 to 800 m2/g for clays.
1 to 0.4 m2/g for silt and 0.04 to 0.001 m2/g for sand.
Calculate the Specific Surface of the following particle:
Gs = 2.6
L = 2.5 mm
W = 1 mm
t = 50 nm
g/m5.1610)05.015.2(6.2
10)05.05.2105.015.2(2S
V..G
A
V.
AS
)g(Mass
)m(AreaSurfaceSurfaceSpecific
2
12
12
S
ws
SSS
2
Example
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Bonds in Clay Minerals
Primary bonds: hold together the atoms (e.g. ionic
bonds or covalent)
Secondary bonds: hold together water molecules of
adjacent sheets of crystalline lattice (e.g. hydrogen
bond of polar molecules or dipoles).
Properties of clay minerals and their reaction with
water are significantly influenced by the hydrogen
bond in water. (Note that water is a dipole )
Basic Blocks in Clay Minerals
Two Basic
Building Blocks
Silica Tetrahedron
(Si4+ surrounded by O2-)
SiO4
Alumina Octahedron
(Al3+ surrounded by OH-)
A B
Silica Sheet Alumina Sheet
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KAOLINITE
A
B
A
B
A
B
A
B
Basic building block
Stacked blocks forming particles
Diameter to thickness ratio: 20
Thickness: 50 nm
Permeability: 10-8 m/s
Activity and swelling potential: Low
Hydrogen bond
Al4Si4O10(OH)8
ILLITE
Basic building block Stacked blocks
forming particles
Diameter to thickness ratio: 50
Thickness: 10 nm
Permeability: 10-9 m/s
Activity and swelling potential: Moderate
A
B
A A
B
A
A
B
A
A
B
A
K K K
K K K
Potassium ion
(Al,Mg,Fe)2(Si,Al)4O10
[(OH)2,(H2O)]
49
MONMORILLONITE
Basic building block Stacked blocks
forming particles
Diameter to thickness ratio: 100 - 400
Thickness: 0.1nm
Permeability: 10-11 m/s
Activity and swelling potential: High
A
B
A
A
B
A
A
B
A
A
B
A
Water
(Na,Ca)0.33(Al,Mg)2(Si4O10)
(OH)2·nH2O
Clay Mineral Specific
Gravity
Specific
Surface
(m2/g)
Liquid
Limit (%)
Plastic
Limit (%)
Kaolinite 2.6 - 2.7 10 - 20 30 - 60 20 - 35
Illite 2.6 - 2.9 65 - 100 60 - 120 35 – 60
Montmorillonite 2.4 - 2.7 700 - 840 100 - 800 50 - 100
Comparison
Smectite Bentonite
50
Clay Activity
m2%
PLLLor
ContentClay%
PIAc
m
Activity Range Classification
Ac ≤ 0.75 Inactive
0.75 < Ac < 1.25 Normal or
Marginally Active
Ac ≥ 1.25 Active
Clay Activity
Soils with high activity are not recommended for use
on landfill liners or contaminated structures as they
are more readily affected by contaminants.
Na - Montmorillonite: Ac = 7.2
Bentonite: Ac = 7
Ca - Montmorillonite: Ac = 1.5
Illite: Ac = 0.9
Kaolinite: Ac = 0.3 - 0.5
51
Pollutant
plume
Leachate loading
Clay soil
barrier
Plume advance
Aquifer
Waste
Plie
Clay Mixed with Contaminants
Effect of Contaminants on Soil
Properties
Bearing Capacity: Decreases
Shear Strength: Decreases
Permeability: Increases
Generally
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103
Clay liner is used as impervious barrier against
drainage of leachate into environment
Clay liner is also used as impervious barrier
against surface runoff into landfill
The important properties of clay liner
Impervious ( k<10-9 m/s )
Limited shrinkage or swelling
Limited cracking potential
Clays in illite group are most suitable
Summary (Clay Liners)
Geosynthetic
Clay Liners
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Geosynthetic Clay Liners
Geosynthetic Clay Liners (GCLs) are thin
hydraulic barriers containing approximately 5
kg/m2 of bentonite, sandwiched between
two geotextiles or attached with an adhesive
to a geomembrane.
Sodium bentonite (lower K) is used primarily
in North America, while calcium bentonite
(higher K) is used more frequently worldwide.
Geosynthetic Clay Liners
Geosynthetic Clay Liners (GCLs) are
increasingly used in bottom liners for
landfills and in final cover for landfills. They
can be easily placed on side slopes.
In a composite landfill liner system, GCLs
reduce the thickness of compacted clay
liners and caps, which increases landfill air-
space in the same footprint and allows less
excavation work for a given landfill volume.
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Geosynthetic Clay Liners
Differential Settlement:
Geosynthetic clay liners can withstand more differential
settlement than compacted clay liners. Hence, GCLs
appear to be an attractive alternative to compacted clay
liners in landfill covers, assuming that other issues such
as slope stability do not preclude the use of GCLs.
L
Differential Settlement: d = /L
2 1
Total Settlement: ? Differential Settlement: ?
Total Settlement: 1
Original Surface
Geosynthetic Clay Liners
Wet-Dry Response (swell and shrink):
Dry bentonite swells when wetted and shrinks
when dried. However the wetting and drying cycles
did not appear to cause any major damage to
GCLs. The geosynthetic component of GCL
prevents any intrusion of overlaying pea gravel
into cracks.
Hence, geosynthetic clay liners can be better
material than compacted clay liners to use,
when some degree of cyclic in water content is
anticipated within the hydraulic barrier.
55
109
Geosynthetic Clay Liners (GCLs)
comprised of sodium bentonite, bound by a woven and non-
woven geotextile or adhered to a geomembrane
110
Properly installed geomembranes in a composite liner
system for a municipal waste landfill
www.bam.de/deponietechnik_en.htm
56
111
Material HDPE
Specification: 1.0 mm
Size: 6m x 50m
Breaking Elongation: 700%
High Density Poly-Ethylene Geomembrane
http://www.geosynthetics.com.cn/UploadFiles/2007516231745880.pdf
112
Model: 5kg/m2
Geotextile + Bentonite Clay
http://www.geosynthetics.com.cn/newsinfo.asp?ArticleID=594
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Q1. Which type of clay is the most suitable soil for construction of clay
liners?
a. Bentonite
b. Illite
c. Montmorilonite
d. Kaolinite
Provide at least two reasons for your selection.
Q2. Landfill compacted clay liners should be compacted very close to the
maximum dry density at:
a. the wet side of the optimum water content.
b. the dry side of the optimum water content.
c. the optimum water content.
d. any water content that clay has got a flocculated structure.
Explain why?
QUIZ
Prefabricated vertical drains (PVDs) are not only
used to accelerate the consolidation process of
compressible soils but were also installed to release
generated gases from landfills.
Generation of landfill gases during the process of bio-
degradation is also a long process like consolidation.
The use of PVDs for landfill gas release was
successfully and extensively applied in landfills in UK
in the early 2000.
Using Prefabricated Vertical Drains for Landfills
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115
Thank you for
your attention
Any
Questions?