1
Geotechnical Aspects of Ballated Rail Tracks
A/Prof Hadi Khabbaz
Email: [email protected]
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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