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)



4





5





6



• Landfill Settlement

• Compacted Clay Liners (CCLs)

– Compaction

– Clay Mineralogy

• Geosynthetic Clay Liners (GCLs)

OUTLINE

7

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

10

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

11

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

12

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

13

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)

14

27

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First layer

Second layer

Third layer

15

29

Fourth layer

Fifth layer

2.51/21.34 = 0.118 or 11.8%

Compacted

Clay Liners

16

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)

32

Compacted Clay Liners (CCLs)

17

www.abgltd.com/Erosamat%20type%203.asp

34 http://www.caawsystems.com/products/images/Geonet%20(3).JPG

18

36

Geomembrane Liners (GLs)

Seam lengths should be monitored carefully

www.ettlinc.com/Ldfl%20CQC-CQA%20Services.HTM

19

37

Clay Liner

20

39

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

40

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.

21

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)

22

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

24

47

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

49

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

50

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:

26

51 http://geotech.uta.edu/lab/Main/SandCone/index.htm

Compaction Mould in the Lab

Volume ≈ 1000 cm3

52

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

27

53 http://www.eleusa.com/pdf/Soil/compaction.pdf

Compaction Hammer

54

Sample Ejector

http://www.eleusa.com/pdf/Soil/compaction.pdf

28

55

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.

56


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

29

57


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

58

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:

30

59 Water Content (%)

Dry

Un

it W

eig

ht

(kN

/m3)

Compaction Curve

MDD = 2.28 t/m3

OMC = 6.8%

60

Effect of Compaction on Soil Structure

Max. dry

density

Optimum

water

content

31

61

Effect of Compaction on Soil Structure

Wet side of

compaction

Dry side of

compaction

62

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

32

63

Field Density

1. Sand Replacement

2. Water or Oil Replacement (Balloon test)

3. Core Recovery Method (for cohesive soils)

4. Nuclear Density Meter

64

Field Density (1)

33

65 http://geotech.uta.edu/lab/Main/SandCone/index.htm

66

34

67

68

35

69

70

Field Density: Water replacement

Check valve

36

71

Field Density: Balloon Test Device

72

Field Density: Oil Replacement

37

73

Lift Height

450 mm

74

Relative Compaction (RC)

100Density Lab Max.

Density FieldCompactionlativeRe

100RCmax(Lab)d,

)field(d

g

g

Can Relative Compaction be greater than 100%?

38

75

Saturated Line (Zero Air Voids)

Zero

Air

Voids

76

Useful Relationships

eSwG rs

Zero Air Voids

Dry Density

w1

wetdry

e1

G wsdry

S

wszav

wG1

.G

Dry Density

39

77

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

78

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.

40

79

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

41

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

42

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

43

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.

44

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

45

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)

46

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

47

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

48

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


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


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

52

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

53

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 (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.

54


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


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

57

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

58

115

Thank you for

your attention

Any

Questions?

6-landfill liners-14s - 2 slides per page

Documents

landfill settlement

settlement of landfill

settlement of msw

early settlement

magnitude of settlement

final settlement

old landfill

landfill operation methods