1

Geotechnical Aspects of Ballated Rail Tracks

A/Prof Hadi Khabbaz

Email: hadi.khabbaz@uts.edu.au

Room 2.511B

Applied

Geotechnics

2

OUTLINE

Introduction to Rail Tracks

Track Substructure Problems and

Investigation

Engineering Properties of Ballast

Application of Geosynthetics in Rail Tracks

Sub-Ballast and Track Filtration

Subgrade Stabilisation

3

Introduction

to Rail Tracks

tangent track (straight line), curved track, and track transition

curve (also called transition spiral or spiral) which connects

between a tangent and a curved track.

Cant-cross level or

Superelevation

Rail Gauge

Wrap

Tilt

Cant Deficiency

Comfort Criterion (jerk) da/dt

(0.2 - 0.5 m/s3)

Vertical Gradient (track grade)

less than 2%

r

tangent track

Important Terms in Rail Track

radrl

maF

r/va2

sinNr/mvF2

cosNmg

mg

F = centripetal force

s

h

hs

htan

22

h

rg

v

mg

r/mvtan

22

hg

svr

2

Curvature and Superelevation

Find curve radius

The ideal cant appears as acceleration deficiency is zero.

Otherwise we have cant deficiency.

realidealdhhh

V = train speed (m/s)

r = curve radius (m)

g = acceleration due to gravity (=9.8

m/s2)

h = cant (m)

s = track width or rail gauge (1.4 m - 1.6

m)

hd = cant deficiency (m)

hreal = real cant

hideal = ideal cant

rg

svh

2

max

ideal

Curvature and Superelevation

Find cant deficiency

2

Given:

Design train speed = 120 km/h

Maximum train speed = 150 km/h

Cant = 160 mm

Gauge = 1500 mm km062.1m1062

8.916.06.3

5.1120

hg

svr

2

22

Example

m250.08.910626.3

5.1150

rg

svh

2

2

2

max

ideal

mm90160250hd

Find:

(a) Curve radius in km

(b) Cant deficiency

Solution:

(b) Cant deficiency

(a) Curve radius in km

The maximum speed of a train on curved track for a

given cant deficiency (unbalanced superelevation) is

determined by the following formula:

d007.0

)mm(h)mm(h)h/km(v

d

max

d = the degree of curvature in degrees per

30m (in railroad work traditionally used 100

ft of chord) d

r

Maximum Speed on Curved Track

Passenger

Train

(km/h)

Freight Train

(km/h)

Branch lines - 30-40

Secondary

lines

80-120 50-80

Main lines 130-200 80-120

High speed

lines

250-300 -

Train Speed

Rolling stock Empty

(kN)

Loaded

(kN)

Trams 50 70

Light-rail 80 100

Passenger coach 100 120

Passenger motor

coach

150 170

Locomotive (4-6

axles)

215 215

Freight wagon 120 225

Heavy haul 120 250-350

Weight per axle of several rolling stock types

(nominal axle load)

Curve Radius

A tilting train is a train that has a mechanism enabling

increased speed on regular rail tracks.

As a train rounds a curve at speed, objects inside the train

experience centrifugal force.

Rail Tracks

Ballasted Tracks

Slab Tracks

Two Main Types of Rail Tracks

3

13

Ballasted Rail Tracks

Ballast

Subgrade

Subballast

Sleeper

Rail-fastening system

Crib Ballast

Shoulder Ballast

Upper Ballast and Lower Ballast

Sub-ballast and Capping Layer

Geosynthetic layer 14

Ballasted Rail Tracks

Ballast

Subgrade

Subballast

Sleeper

Rail-fastening system

Fresh Ballast Recycled Ballast

Blended Ballast

Future Alternatives to Ballasted Tracks

Ballast breakage, excessive

settlement and fouling of

ballasted track

Intensive maintenance of rial

tracks

Rail Organisations are

interested in alternative,

non-ballasted track systems.

Non-ballasted Track Systems

1. Slab Track

(Ballast-less Tracks)

2. Magnetically Levitated Trains

(Maglev-Trains)

Slab Track (Ballast-less tracks)

In a slab track the load-carrying capacity is

fulfilled by reinforced or pre-stressed concrete

slabs, which rest on a sand bed and support the

rails above via directly attached concrete

sleepers or via a cast embedment of rubber.

Slab Track Main Benefits

Increased service life

Relatively low structural weight and height

High lateral track resistance allowing higher speeds in

combination with tilting technology

Great precision of track-geometry parameters by

application of precise concrete sleepers

Limitation of churning of ballast particles at higher speeds

Low maintenance costs if the sub-structure has sufficient

strength and resiliency to prevent cracking of the concrete

Higher availability due to less closure of tracks for

maintenance requirements

4

Slab Track (Ballast-less tracks)

Integration of Sleepers with the Concrete

To reduce the high construction costs of high-speed

rails, a new installation concept, called Rheda

System, was developed by Rail-One company in

Germany in 2000: Integration of sleepers with the

concrete

Ballast-less (Slab Track) Construction

Track Structure

1. Discrete supported rail 2. Embedded rail

Slab Track Drawbacks

Higher construction costs

The time-consuming structural precautions that have to

be taken to avoid differential settlements and cracking of

the slabs.

Large alterations in track position and superelevation can

only be made possible by substantial amounts of work,

Adaptability to larger displacements in the embankment

is relatively small.

In case of derailment, repair works will take much more

time and efforts.

5

Maglev-Trains

A non-conventional

railway system that has a

large potential for future

application is the

magnetically levitated train

(‘Maglev-Train’).

For this railway system, frictional contact between the

train wheel and the rail is avoided by applying a

magnetic field that levitates the train to a distance of

100 mm above the track.

http://www.pieces-zine.com/200902magnet/images/Maglev.jpg

Maglev-Trains

In 1997, at a 43 km test track in Yamanashi, Japan, a Maglev train

established a new world speed record of 550 km/h.

Despite of the speed increase, the very low level of noise and

vibrations, and the low maintenance, the costs of this type of railway

system are significantly higher than those of a conventional railway

system.

http://etumbv.nl/vestipendo/maglev.jpg

The magnetic field is generated

by using super-conducting

magnet coils, which are made of

very thin wires of a niobium-

titanium alloy that are brought

into copper wires.

27

Track Substructure

Problems and

Investigation

28

Problems in Rail Track Substructure

29

Track Problems

Why do we need to know track

problems?

Having a clear idea of the problem to find

solutions

Determining the level of track reconditioning

Using the past problems occurred for new

designs, hence, to reduce the maintenance

costs 30

FOUNDATION

• Differential settlement

• Clay pumping

• Ballast breakage and fouling

• Poor drainage

OTHER

• Rail irregularities – rail joints, dipped welds,

railhead corrugation

• Transition effects – bridge and grade crossings

• Track buckling

Track Problems

6

31

Differential Settlement

Due to different rates and amounts of settlement

mainly in the ballast and subgrade. Can also result

from lateral spread of ballast

32

Clay Pumping

Under cyclic loading and in presence of water, subgrade

materials ‘pump’ up into the ballast. More common when

no subballast layer is used.

33 Clay Pumping

34

Ballast Breakage and Fouling

Ballast breaks under cyclic loading. Foreign materials,

clay from the subgrade and broken ballast fill the

ballast voids and the track becomes ‘fouled’.

2 November 2010, The Canterbury Earthquake in New Zealand

An image of the distorted railway line 36

EXAMPLES OF TRACK FORMATION PROBLEMS

Ballast Fouling

7

37

Foundation Rock Pumping

38

Foundation Rock Pumping

39

Poor Drainage-Undrained Bearing

Ballast is supposed to be

free draining even at

highest level of compaction

Native Vegetation

(weeds!) to improve Soil

Suction

Can be due to poor

drainage design, poor

subgrade conditions and/or

ballast fouling

40

Poor Drainage - Continued

41

Issues: Track stability

Waterlogging

Fire & weed management

Adjacent land use

Poor Drainage - Continued

42

INITIAL FORMATION

Subgrade

Ballast (Base)

Poor Drainage - Continued

8

43

ENTRY OF MOISTURE INTO

BASE

MOISTURE EXITS OUT SHOULDERS

Poor Drainage - Continued

44

ENTRY OF MOISTURE

INTO SUBGRADE

MOISTURE IS TRAPPED

Poor Drainage - Continued

45

Poor Drainage - Continued Foundation Failure

Punching Failure

Bearing Capacity and Slope Instability

46

Track buckles due to build up of stress in the welded rail

As a result of heat and insufficient lateral stability to hold

the track

Heat Buckle

Track Buckling Poor Design and Construction

9

More Specific Problems of Tracks

Ballast degrades and deteriorates with increasing train

passages, causing reduced angularity and shear

strength, resulting in higher track deformation and

differential settlement.

Particle breakage (degradation) is a major cause of

ballast fouling.

Severely fouled ballast is usually replaced by fresh

aggregates during track maintenance, which costs

millions of dollars annually.

Large stockpiles of waste ballast are causing

environmental concern and expensive to dispose off.

How to minimise ballast degradation and how the

waste ballast can be recycled to track substructure. 55

Engineering

Properties of

Ballast

Provide Rapid

Drainage Reduce Settlement

and Lateral

Displacement

Withstand High

Dynamic Loads:

Shear Strength

Minimising Ballast Degradation is Imperative to Sustain

its Primary Functions

BALLAST FUNCTIONS

Individual

particles

• Mineralogy

• Durability

• Shape

• Texture

• Specific gravity

Assembly of

particles

• Permeability

• Void ratio

• Moisture content

• Bulk density

Parent rock

characteristics

· Hardness

· Specific gravity

· Toughness

· Weathering

· Mineralogical composition

· Internal bonding

· Grain size

Ballast particle

properties

· Existing Fractures

· Particle shape

· Particle size

· Surface texture

Field or experimental

parameters

· Confining pressure

· Thickness of ballast layer

· Ballast gradation

· Moisture content

· Initial density or porosity

· Train load and speed

0 5E+5 1E+6

Number of load cycles, N

0

5

10

15

20

Se

ttle

me

nt,

s (

mm

) s = a N b

Latite basalt, air dry

d50

= 43.4 mm

30 tonnes/axle

25 tonnes/axle

25 & 30 tonnes/axle

a = 8.15

b = 0.044

a = 8.7

b = 0.044

a = 6.9

b = 0.044 a = 6.7

b = 0.044

500,000 1,000,000

Effect of Load Cycles

and Axle Loads on Ballast Settlement

baNS

10

Ballast Grading RailCorp

Recommended Railway Ballast Grading

0

20

40

60

80

100

1 10 100

Particle size (mm)

% P

as

sin

g

Recommended Grading

Australian Standard (AS 2758.7)

Cu = 2.2 - 2.6

Cu = 1.5 - 1.7

Uniformity Coefficient: Cu = D60/D10

Large-Scale Cylindrical Triaxial Apparatus

Monotonic Loading Cyclic loading

Diameter = 300 mm

Height = 600 mm

Dynamic actuator

installation

Large Scale Dynamic

Triaxial Equipment

Built at University of Wollongong

Diameter = 300 mm

Height = 600 mm

1020 30 40 50 60 70

Particle Size (mm)

0

20

40

60

80

100

Pe

rce

nta

ge

Pa

ssin

g

Very Uniform (VU)

Uniform (U)

Gap (G)

Moderate (M)

VU

U

G

M

Cu

1.39

1.72

1.68

2.03

k0 (m/s)

9.9

7.6

8.1

5.0

e0

0.82

0.77

0.74

0.71

Particle Size Distribution of Saples

PSD of samples used in large-scale triaxial testing

0 100000 200000 300000 400000 500000

Number of Cycles

-3

-2

-1

0

Vo

lum

etr

ic S

tra

in

v (

%)

0

2

4

6

Axia

l S

train

1 (

%)

Very Uniform

Uniform

Gap

Moderate

Axial

Volumetric

v = 1 + 23

Axial and Volumetric Strains

Axial and Volumetric Strains response of different ballast particle

distributions under cyclic loading

11

1 .2 1 .4 1 .6 1 .8 2 2 .2

C u

0

1

2

3

4

Bre

ak

ag

e (

%)

V e ry U n ifo rm

U n ifo rm

G a p

g ra d e dM o d e ra te ly

g ra d e d

Role of Particle Gradation on Ballast Breakage Ballast Breakage Indices

1. Marsal Method (1973)

2. Hardin Method (1985)

Determination of Particle Breakage

a

b

c

d

fikWkWk%W

final

fWk

iWk

)dc()ba(%Wk

initial

n

1

kgWB

0Wifk

Example to find Breakage Index (Bg)

n

1

kgWB 0Wif

k

%5.53105.402Bg

Grain Size (mm)

2mm 60mm

Before

Loading

After Loading

HARDIN METHOD

2mm 60mm

Bp

Potential Breakage

12

2mm 60mm Bt

Total Breakage

(Red Area)

2mm 60mm

Br (%) = 100 x (Bt / Bp)

127.75

3.46

2.71

Relative Breakage

Fouling Index

Fouling Index = P4 + P200

P4 = Percent passing the 4.75 mm sieve

P200 = Percent passing the 0.075 mm sieve

FI < 1 : Clean Ballast

1 <FI 10 : Moderately Clean Ballast

10 <FI 20 : Moderately Fouled Ballast

20 <FI 40 : Fouled Ballast

FI > 40: Highly Fouled Ballast

Ballast Fouling due Coal Particles

Infiltration of

coal

VCI = (1+ef)

eb

× Gs.b

Gs.f

× Mf

Mb

× 100

Void Contaminant Index (VCI) proposed by UOW

eb = Void ratio of clean ballast

ef = Void ratio of fouling material

Gs-b = Specific gravity of clean ballast

Gs-f = Specific gravity of fouling

Mb = Dry mass of clean ballast

Mf = Dry mass of fouling material

Clay infiltration

Ballast Fouling Assessment

VCI = (1+ef)

eb

× Gs.b

Gs.f

× Mf

Mb

× 100

Void Contaminant Index (VCI) proposed by UOW

PVC = Vf

Vvb

× 100

Percentage Void Contamination (PVC)

Feldman and Nissen (2002)

Fouling Index (FI)

Selig and Waters (1994)

FI = P4.75 + P0.075

P4.75 = Percentage (by weight) passing the 4.75 mm sieve

P0.075 = Percentage (by weight) passing the 0.075 mm sieve

Vvf = Total volume of fouling material passing 9.5 mm sieve

Vvb = Initial voids volume of clean ballast

eb = Void ratio of clean ballast

ef = Void ratio of fouling material

Gs-b = Specific gravity of clean ballast

Gs-f = Specific gravity of fouling

Mb = Dry mass of clean ballast

Mf = Dry mass of fouling material

0

1 0

2 0

3 0

4 0

5 0

0

2 0

4 0

6 0

8 0

1 0 0

0 5 1 0 1 5 2 0 2 5

0

2 0

4 0

6 0

8 0

1 0 0

Fo

uli

ng

In

de

x,

%

c o a l- fo u le d b a l la s t

s a n d -fo u le d b a l la s t

c la y -fo u le d b a l la s t

PV

C,

%

VC

I, %

P e r c e n ta g e fo u lin g , %

Ballast Fouling

Assessment:

A Comparison

clay

coal

sand

clay

sand

VC

I%

PV

C%

F

ou

lin

g

Ind

ex

%

Percentage of Fouling, %

13

Permeability Coefficient

Hazen formula: K = 0.01(D10)2

Sherard formula: K = 0.0035(D15)2

Indraratna et al: K = 0.01(D5D10)0.93

NOTE: K is in m/s, and Dn is in mm

Sieve Size

(mm)

Before

Loading (%)

After

Loading (%)

63 100 100

53 85 89

45 60 70

37.5 45 50

26.5 16 32

19 6 13

13.2 2 10

9.5 1 8

4.75 0.5 6

2.36 0 3

1.18 0 2

0.6 0 1.5

0.30 0 1.3

0.150 0 1.1

0.075 0 0

Question:

Find the breakage

indices (Bg and Br)

fouling index (FI)

and Permeability

Coefficient (K) of

this ballast.

Role of Particle Gradation

The more well graded ballast:

• Smaller the particle breakage,

• greater the internal friction,

• Smaller the ballast settlement,

• Smaller the lateral movement

but, lower the drainage rate.

Effect of Confining Pressure on Particle

Degradation (Cyclic Loading)

0 5 0 1 0 0 1 5 0 2 0 0 2 5 0

E ffe c tiv e C o n f in in g P re s s u re (k P a )

0

0 .0 2

0 .0 4

0 .0 6

Ba

lla

st

Bre

ak

ag

e I

nd

ex

, B

BI

qm a x

= 5 0 0 k P a

qm a x

= 2 3 0 k P a

( I ) ( I I ) ( I I I )

Optimum Contact

Track buckles due to build up of

stress in the welded rail

as a result of heat and insufficient

lateral stability to hold the track

Heat Buckle at Darnick, NSW

SHOLDER BALLAST

ARTC

14

BALLAST SHOULDER WIDTHS

RailCorp

Long Welded Rail : LWR

Continuously Welded Rail : CWR

BALLAST DEPTH CATEGORIES

RailCorp

CBR: California Bearing Ratio The California Bearing Ratio was developed by the California State Highways Department.

A simple test developed to evaluate the strength of road subgrades.

Minimum CBR for Formation

88

Applications of

Geosynthetics in

Rail Tracks Reinforcement

Creep strength

Primary Functions of

Geosynthetics

Geogrids Geotextiles Geomembranes Geocomposites

Separation

Filtration

Drainage

Protection

Moisture Cutoff

Separation

Separation

Reinforcement

Filtration

Drainage

GEOSYNTHETICS

15

Extruded Geogrids (Uniaxial) Biaxial Geogrids

1.2-1.5 d50 of ballast

Geocell

Strengthening of Rail Tracks Using Geosynthetics

Woven Geotextile

Geocomposite

(Bonded Geogrid & Geotextile)

Recycled Ballast

from Chullora Quarry, Sydney

Improvement of Recycled Ballast Using Geosynthetics

Fresh Ballast

from Bombo Quarry

near Wollongong

Geotextile

Geogrid

800

600

600

Large-scale rig with servo hydraulic actuator and unrestrained walls

16

Load bearing

ballast

300

100 Capping

50 Subgrade

150 Crib ballast

Specimen Preparation in Prismoidal

Triaxial Chamber

Pressure cell and settlement plates installation

Placement of pressure cell and

settlement plates on the top of the

Geosynthetic layer

0

2 0

4 0

6 0

8 0

1 0 0

1 0 1 0 0

S ie v e s iz e (m m )

% P

as

sin

g

B a lla s t b e fo re T e s t in g (R e c y c le d / F re s h )

S R A U p p e r L im it S p e c if ic a t io n

S R A L o w e r L im it S p e c if ic a t io n

5 02 0 3 0 4 0 8 06 0 7 0 9 0

S ta te R a il A u th o r i ty o f N S W (S R A )

S R A s p e c if ic a t io n T .S . 4 3 0 2 -1 9 8 3

Cu = 1.6

Cz = 1

D50 = 35 mm

g = 15.3 kN/m3

Particle Size Distribution of Ballast before Testing

0

5

10

15

20

25

0 100000 200000 300000 400000 500000 600000

Number of load cycles, N

Sett

lem

en

t, S

(m

m)

Fresh ballast (wet)

Recycled ballast (wet)

Recycled ballast with geotextile (wet)

Recycled ballast with geogrid (wet)

Recycled ballast with geocomposite (wet)

Stabilisation

Rapid increase

in settlement

Recycled ballast (saturated specimens)

NOTE: Results for Fresh Ballast specimens and Recycled Ballast (dry specimens) are not shown here

Settlement of ballast with and without geosynthetics

-2.0

-1.5

-1.0

-0.5

0.0

0 100000 200000 300000 400000 500000 600000

Number of load cycles, N

Late

ral str

ain

, L

(%

)

Fresh ballast (dry)

Fresh ballast with geotextile (dry)

Fresh ballast with geogrid (dry)

Fresh ballast with geocomposite (dry)

(L is parallel to the sleeper)

Recycled ballast (saturated specimens)

Variation of lateral strain of ballast under cyclic loading

-6

-4

-2

0

2

4

0 10 20 30 40 50 60 70

Grain size (mm)

DW

k (

%)

Fresh ballast (wet)

Recycled ballast (wet)

Recycled ballast with geotextile (wet)

Recycled ballast with geogrid (wet)

Recycled ballast with geocomposite (wet)

Effect of geosyntheticsHighest breakage

Recycled ballast (saturated specimens)

Change in particle size of ballast under cyclic loading

17

3 .1 9

2 .9 6

1 .6 3

1 .5 0

1 .8 8

1 .7 01 .6 4

1 .5 61 .6 0

1 .5 2

0 .0

0 .5

1 .0

1 .5

2 .0

2 .5

3 .0

3 .5

Bre

ak

ag

e I

nd

ex

R e c y c le d b a lla s t F re s h b a lla s t R e c y c le d b a lla s t

w ith g e o g r id

R e c y c le d b a lla s t

w ith g e o te x t ile

R e c y c le d b a lla s t

w ith g e o c o m p o s ite

S a tu ra te d S a m p le s

D ry S a m p le s

R B

(g e o g r id )

R B

(o n ly ) R B

(g e o te x t ile

)

R B

(g e o c o m p o s ite

)

F B

(o n ly )

R B : R e c y c le d B a lla s t

F B : F re s h B a lla s t

Breakage Indices of Specimens with and without Geosynthetics

1 6 .5 7

1 2 .21 2 .6 3

2 3 .4 5

1 6 .9 8

1 5 .1 1

0

5

1 0

1 5

2 0

2 5

R e c y c le d B a lla s t F re s h B a lla s t

R e c y c le d B a lla s t w ith

G e o c o m p o s ite

To

tal

se

ttle

me

nt

(mm

)

D ry S a m p le s S a tu ra te d S a m p le s

Total Settlement

Settlement of dry and wet samples after 500,000 cycles

104

Sub-Ballast and

Track Filtration

105

Rail Track Sub-Ballast

Ballast

Subgrade

Subballast

Sleeper

Rail-fastening system

Works as a separator

Distributes load on subgrade

Works as a filter

Sub-Ballast Purpose

106

Track Degradation Modes

Ballast fouling

Clay pumping

Hydraulic erosion of

ballast and sleepers

Sleeper 1%

Subgrade 3%

Surface 7%

Underlying

granular layer

13%

Ballast 76%

107

Consequences of Fouled Tracks

Less ballast life High risk of derailment Speed restrictions High maintenance costs Recurrence of problem

18

108

How Does Filter Work?

Track filter must meet 2 criteria:

Retention: Fine enough to capture eroded particles within its

voids

Permeability: Coarse enough to allow seepage flow

109

Filtration

Permeability

8 51 5

5 dD

5 05 0

2 5 dD

2 0

1 0

6 0

D

DC

u

1 51 5

5~4 dD

GRAVEL Coarse Fine

SAND SILT or CLAY

Coarse Fine Medium

0

10

20

30

40

50

60

70

80

90

100

0.001 0.01 0.1 1 10 100

Grain size [mm]

Pe

rce

nt fin

er

by w

eig

ht

[%]

Ballast grading limits

by AREA No. 4

Fine-grained

subgrade

≤ 25

Suballast

grading limits

GRAVEL Coarse Fine

SAND SILT or CLAY

Coarse Fine Medium

0

10

20

30

40

50

60

70

80

90

100

0.001 0.01 0.1 1 10 100

Grain size [mm]

Pe

rce

nt

fin

er

by w

eig

ht

[%]

Ballast grading

limits by AREA

No. 4

Fine-grained

subgrade Suballast

coarse

grading

limits

Suballast

fine

grading

limits

Subballast Selection Criteria

(Selig and Waters, 1994)

Dn = particle size which passes n% by

weight of the total filter sample

dn = particle size which passes n% by

weight of the total base sample

(Piping ratio)

112

Subgrade

(Formation)

Stabilisation

Increase soil stiffness & shear strength

Reduce pore water pressure

Reduce lateral displacement

Improvement of Soft Formation

Remediation Techniques

Three Methods

Chemical Stabilisation Cement, Lime and Lignin

Vertical Drains Vacuum Preloading

Native

Vegetation

Soft Clay Underlying Rail Tracks Improved by

Vertical Drains

Entry of Moisture into Base

MOISTURE EXITS OUT SHOULDERS

Using Native Vegetation (Trees)

19

MOISTURE IS TRAPPED

Entry of Moisture into Base

Tree roots favour surface water source

119

Uniformly graded ballast particles are more prone to

degradation.

Conclusions

Confining pressure plays a vital role in controlling dilation-

compression behaviour of ballast.

Ballast deformation varies non-linearly with the number of

load cycles.

120

The use of thicker and more durable geotextiles is very

important to maintain the long term performance of them.

Conclusions

Presence of the geosynthetic reinforcement can reduce

the compressibility of the track.

Reduced breakage of the ballast material and greater

abrasion resistance can be achieved with geosynthetics.

The greater lateral confinement can be provided by

geosynthetics (reinforcement layer).

Using geo-composites decreases settlement, lateral

movement, particle degradation and subgrade pumping. 122

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