Railway Technical Research Institute Railway Technical Research Institute Geotechnical issues around ballasted track and slab track in Japan Railway Technical Research Institute Yoshitsugu Momoya 1
Railway Technical Research InstituteRailway Technical Research Institute
Geotechnical issues around ballasted
track and slab track in Japan
Railway Technical Research Institute
Yoshitsugu Momoya
1
Railway Technical Research InstituteRailway Technical Research Institute
Contents
Introduction
Ballasted tracks in existing line
Asphalt roadbed in design standard
Slab track on earth structure
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Ballasted track and slab track
Ballasted track • Periodical maintenance work is necessary.
• Easy to correct track irregularity.
• Construction cost is relatively low.
Slab track
• Low maintenance work.
• Difficult to correct track irregularity.
• Construction cost is relatively high.
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Supporting sleepers stably and uniformly.
Ballast
Roadbed
Subgrade
Wheel load of train
20%10% 20% 10%40%
Distribute train load applied on roadbed.
Requirement for ballasted track
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Easy to correct track irregularity by tamping.
Requirement for ballasted track
Good drainage.
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Apply adequate elasticity on track (especially on bridge or viaduct)
Requirement for ballasted track
Lateral resistance against lateral train load and rail buckling.
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Requirement for slab track
Maintenance free.
Not high construction cost.
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Soft ground.
Present coast line
Coast line 6000 years ago
Tokyo
Alluvial clays are deposited at plains. Geological ages are young. (younger than 6000 years)
Difficult circumstance for railway track in Japan
Mud pumping on soft ground
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Heavy rain.
Japan
China
Rain fall in September (average)
Ballasted track after rain
Difficult circumstance for railway track in Japan
Typhoon
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Contents
Introduction
Ballasted tracks in existing line
Asphalt roadbed in design standard
Slab track on earth structure
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Existing line
・Constructed before 1960’s
Design standard was not regulated.
Newly constructed line
・Constructed after 1970’s
Design standard was established in 1978
Most of railway lines in Japan were constructed before 1950’s
Existing line and newly constructed line
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Roadbed and subgrade in existing line
• No specific roadbed layer • Material is not regulated • Insufficient drainage • Low stiffness subgrade
• Penetration of ballast into roadbed • Mud pumping • Large dynamic deformation • Increase of maintenance work
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Penetration of ballast into roadbed
Existing line
Ballast layer SPT test N-value Ballast penetration layer
SPT test N-value
Roadbed
Subgrade
Subgrade
Dep
th (
cm)
Dep
th (
cm)
Newly constructed line
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Depth of ballast penetration layer
0 50 100 150 200 250 300 0
30
60
90
120
150
Logeh=-0.019K30+5.02
道床バラスト貫入層の深さ(
cm)
地盤の K30値(MN/m3)
Dep
th o
f b
alla
st p
en
etra
tio
n la
yer
(cm
)
K30 value of plate loading test (MN/m3)
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Subgrade
Ballasted track
3.0m
Vertical stress in roadbed and subgrade
0.0 1.0 0.5 Ballast
Roadbed
Vertical stress in roadbed and subgrade
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Settlement of ballasted tracks and track irregularity strongly depends on the stiffness of roadbed and subgrade.
Track irregularity
mm/10,000 ton
Am
plit
ude o
f ro
adbed
dis
pla
cem
ent
(mm
)
Stiffness of roadbed and track irregularity
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Most of the roadbeds constructed before 1960’s do not have sufficient stiffness.
Large settlement
Without improvement
Roadbed improvement Less settlement
Roadbed improvement
Settlement of ballasted track becomes less after roadbed improvement.
Roadbed improvement
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Conventional roadbed improvement method:
Crushed stone, steel slag, cement treated material.
Sufficient compaction work was necessary.
Conventional roadbed improvement
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Liquid A
Liquid B
Pump
Pump
Grout
Plastic pipe
Slag cement Setting accelerator Water
Hardening agent Water
発生バラストの投入(バラスト+硅砂)
グラウトの注入Grout
Contaminated
ballast by sand
Degraded ballast
(Mixed with sand)
New roadbed improvement method
Reusing degraded ballast mixed with cement grout.
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Cyclic loading 5Hz, ΔP=80kN
Sleeper
Ballast
Roadbed
Cyclic loading test
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0 200 400 600 800 1000-25
-20
-15
-10
-5
0
Water pouring
Grouted deteriorated ballast
Grouted new ballast
Sand roadbed
Se
ttle
me
nt o
f sle
ep
er
(mm
)
Number of cycles (x1000)
Water pouring
Cyclic loading test results
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750 800 850 900 950 1000-2.5
-2.0
-1.5
-1.0
-0.5
0.0
Groudted degraded ballast
Grouted new ballast
Sand roadbed
Se
ttle
me
nt o
f sle
ep
er
(mm
)
Number of cycles (x1000)
Cyclic loading test results
Settlement after 750,000 cycles
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Before roadbed improvement Excavation of ballasted track
Degraded ballast Preparation of grout
Liquid A
Degraded ballast
Grout material
Liquid B
Application at site
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Injection of grout
Injection of grout After roadbed improvement
Laying degraded ballast
Application at site
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0 5 10 15-30
-20
-10
0
10
20
30
高低
変位
(mm
)
位置(m)
未対策
0 5 10 15-30
-20
-10
0
10
20
30
高低
変位
(mm
)
位置(m)
未対策
6ヵ月後
0 5 10 15-30
-20
-10
0
10
20
30
高低
変位
(mm
)
位置(m)
未対策
11ヵ月後
6ヵ月後
路盤改良範囲Roadbed improvement
After 6 months
After 11 months
Before improvement
Tra
ck
irre
gu
lari
ty(m
m)
Position (mm)
Track irregularity after the roadbed improvement
Position (m)
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Concrete
structureEmbankment
Structuraltransition
Generalsection
Concrete structure
Embankment
Floating sleeper
→ large settlement
Structural transition
zone
No floating sleeper
Issues around transition zone
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Loading actuators
Track model
Scale: 1/5
Embankment
model
Load cells
Concrete
structure
model
Moving loading test
Multi-actuator moving loading test apparatus
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Multi-actuator moving loading test apparatus
Posoition of virtual axial load
Load
Actuator No.1No.2 No.3 No.4 No.5 No.6 No.7 No.8
Virtual axial load (combined actuator load)
No.1+No.2 No.2+No.3 No.3+No.4 No.4+No.5 No.5+No.6 No.6+No.7 No.7+No.8
Load by each actuator
vehicle vehicle
2.1 11.7 2.1 2.1 11.7 2.14.1
Unit: m
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Multi-actuator moving loading test apparatus
0 10 20 30 40 50
0
1
2
Act
uat
or
load
(kN
)
Time (sec)
9.0 9.5 10.0 10.5 11.0 11.5 12.0
0
1
2
Act
uat
or
load
(kN
)
Time (sec)
0 10 20 30 40 50
0
1
2
Sle
eper
load
(kN
)
Time (sec)
0 10 20 30 40 50
-2
-1
0
Sle
eper
dis
pla
cem
ent
(mm
)
Time (sec)
Sleeper settlement Sleeper load
Actuator load Actuator load
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Train load
Embankment Concrete
structure
-500 0 500 1000 1500
0
1
2
3
4
Sle
eper
load (
kN)
Sleeper position (mm)
Concrete Embankment
Sleeper load 4000cycles
0 500 1000 150012
10
8
6
4
2
0
Se
ttle
me
nt
of
sle
ep
er
(mm
)
Position of sleeper (mm)
Sleeper settlement 10 trains
50 trains
100 trains
200 trains
Those sleepers are not
supporting wheel load
(Floating sleeper)
Accelerate local settlement
Moving loading test results
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Moving loading test results
Concrete slab Low stiffness mat
Concrete approach slab
Approach block (Design standard)
Low stiffness roadbed
Approach block
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-500 0 500 1000 150012
10
8
6
4
2
0
Approach block
Settle
ment
of sle
eper
(mm
)
Position (mm)
Without counter measure
Concrete approace slab
Concrete Embankment
Low stiffness roadbed
Moving loading test results
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Contents
Introduction
Ballasted tracks in existing line
Asphalt roadbed in design standard
Slab track on earth structure
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Asphalt roadbed for newly constructed lines
Asphalt concrete
Well graded crushed stone
Asphalt roadbed became standard structure in Japan after 1978
Subgrade: K30 ≧ 70MN/m3
• Sufficient bearing capacity.
• No ballast penetration.
• Good drainage.
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Asphalt concrete layer Asphalt concrete layer
Railway Road
Multi-layered elastic analysis FEM analysis
Wheel
Rail Sleepers
Ballast
Subgrade Subgrade
Tensile strain Tensile strain
Design of asphalt roadbed
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Design of asphalt roadbed
Asphalt concrete
Well graded crushed stone
Subgrade
Displacement at the surface of roadbed
Tensile strain at the bottom of asphalt concrete
Subgrade
Well graded crushed stone
Asphalt concrete
Rail Sleeper
Ballast
1/4 symmetric model
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0 60 120 180 240 300 360 420 4803.0
2.5
2.0
1.5
1.0
0.5
0.0
Thickness of crushed stone layer:
15cm
30cm
60cm
Dis
pla
cem
en
t o
f asp
halt
ro
ad
bed
su
rface (
mm
)
Position (cm)
Wheel load 80 kN
(bogie axle)
0 60 120 180 240 300 360 420 480-60
-40
-20
0
20
40
60
Between sleeper:
Compressive strain
Beneath sleeper:
Tensile strain
Wheel load 80 kN
(bogie axle)
Thickness of crushed stone layer
15cm
30cm
60cm
Str
ain
at
the b
ott
om
of
asp
halt
co
ncre
te (
)
Position (cm)
Settlement Strain
Design of asphalt roadbed
Asphalt concrete
Well graded crushed stone
Subgrade
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・Tensile strain at the bottom of asphalt concrete εt
→ Allowable number of cyclic loading for Fatigue failure
NA = 0.6×18.4×C×6.167×10-5 et -3.291EA
-0.854 Where NA :Allowable number of cyclic loading for Fatigue failure et :Tensile strain EA :Young’s modulus (MN/m2) Vv :void ratio Vb : asphalt volume C = 10M M = 4.84 (Vb / (Vv+Vb) - 0.69)
・Vertical displacement at the surface of asphalt roadbed
→ Less than 2.5mm considering impact load
Design of asphalt roadbed
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Fatigue life
Subgrade Thickness of crushed stone
layer for high speed line
K30 = 70 MN/m3 60 cm (Settlement)
K30 = 110 MN/m3 40 cm (Fatigue life)
Design of asphalt roadbed
0 10 20 30 40 50 60 70 801
10
100
1000
Subgrade: K30
= 70 MN/m3
Subgrade: K30
= 110 MN/m3
Thickness of crushed stone layer (cm)
Fat
igu
e li
fe o
f as
ph
alt
con
cret
e (y
ear)
40years
Displacement
0 10 20 30 40 50 60 70 800
1
2
3
4
2.5mm
Subgrade: K30
= 70 MN/m3
Subgrade: K30
= 110 MN/m3
Thickness of crushed stone layer (cm)
Dis
pla
cem
ent
of
asp
hal
t ro
adb
ed (
mm
)
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Contents
Introduction
Ballasted tracks in existing line
Asphalt roadbed in design standard
Slab track on earth structure
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Slab track
鉄道総研 RRR 堀池 2007.6
Rail
Cement asphalt mortar
Slab
Rail Fastener
Concrete trackbed
Circular stopper
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Tokaido Shinkansen (1964): Ballasted track on embankment Bearing capacity of embankment was not very high. (using clay, compaction control etc) Settlement of ballasted track became very large after the start of train operation. Sanyo Shinkansen Okayama-Hakata (1975): Slab track on viaduct. Hokuriku Shinkansen Takasaki-Nagano (1997): Slab track on high quality embankment
http://www.jrtt.go.jp/02Business/Construction/const-seibi.html
History of slab track
Sanyo
Tokaido
Hokuriku
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Life cycle cost of slab track is lower than that of ballasted track.
9 years
Year
Tota
l co
st
Annual tonnage 1.2 million ton / year
Cost of slab track
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0
20
40
60
80
100
割合
(%
)
バラスト軌道 スラブ軌道等
東海道新幹線
(
東京・新大阪)
山陽新幹線
(
新大阪・岡山)
山陽新幹線
(
岡山・博多)
上越新幹線 (
大宮・新潟)
東北新幹線
(
東京・盛岡)
北陸新幹線
(
高崎・長野)
東北新幹線
(盛岡・新青森)
九州新幹線
(
博多・鹿児島中央)
北陸新幹線
(
長野・金沢)
北海道新幹線
(
新青森・新函館)
九州新幹線
(
武雄温泉・諫早)
Ballasted track
Slab track
Toka
ido s
hink
anse
n
San
yo s
hink
anse
n
Jyo
etsu
shi
nkan
sen
Toho
ku s
hink
anse
n
Hoku
riku
shi
nkan
sen
Kyu
syu s
hink
anse
n
Hokk
aido
shi
nkan
sen
Kyu
syu s
hink
anse
n
Hoku
riku
shi
nkan
sen
Toho
ku s
hink
anse
n
San
yo s
hink
anse
n
Perc
enta
ge (
%)
1964 1975 1982 1997
Percentage of slab track in Shinkansen
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Slab track on earth structure
Required specification for subgrade Stiffness: K30 ≧ 110MN/m3
Density: Higher than 95% of maximum dry density Material for embankment: Gravel, Sandy gravel, Gravelly sand, sand
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ap
h
∞
E1,μ1
E2,μ2原地盤
路床改良層
20 30 40 50 60 70 80 90 100 1100.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
改良深さ(
m)
原地盤のK30値 (MN/m
3)
Multi-layered elastic analysis
Subgrade improvement for slab track
• Subgrade of natural ground should be improved to satisfy K30 value.
Subgrade
Improved layer
K30 value of natural ground (MN/m3) Depth
for
impro
vem
ent
(m)
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列車輪重
レール
軌道スラブ
仮想部材(軌道パッド)
仮想部材(CAモルタル)
鉄筋コンクリート版
路床
路 床
鉄筋コンク
リート版
軌道スラブ
レールCAモルタル
軌道パッド
鉄筋コンクリート版
鉄筋コンクリート版
仮想部材(CAモルタル)
軌道スラブ
路 床
3 200mm
軌道スラブ
CAモルタル
路 床
軌道パッド
レール
列車輪重
(a) Parallel to rail direction (b) Perpendicular to rail direction
Reinforced concrete
Slab Rail
Rail pad CA mortar
Subgrade
Slab
Train load Rail Rail pad
CA mortar
Reinforced concrete Subgrade
Train load Rail
Slab CA mortar
Reinforced concrete
Rail pad
Train load
Slab
CA mortar
Subgrade
Subgrade
Reinforced concrete
Numerical analysis for the design
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Co
ncr
ete
ro
adb
ed
Trac
k
CA mortar
Reinforced concrete
Well graded crushed stone
Prime coat
Sub
grad
e
(em
ban
kmen
t)
Slab
Subgrade (Groundwork or cutting)
Drainage Layer
Slab
Filling layer (CA mortar)
Reinforced concrete
Well graded
crushed stone
Slab track on earth structure (Cutting)
Slab
Concrete roadbed
Cross section of slab track on earth structure
Subgrade
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Subgrade (K30
≧110 MN/m3)
Standard
RC roadbed
Slab
track
Reinforced concreteWell-graded crushed stone
• If N value of subgarad by SPT test is less than 4, ground improvement is required.
Subgrade with N value less than 4
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Integrated RC roadbed
Slab
track
Clay subgrade(N<4)
Integrated
RC roadbed
Surface improvement
Ground improvement is necessary
in the standard design method
Reinforced concrete Well-graded
crushed stone
Investigation was carried out to apply integrated RC roadbed on soft diluvial clay subgrade.
Diluvial clay: Ageing effect, pre-loaded(cutting)
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Ground investigation method
Electric cone penetration test Standard penetration test
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Ground investigation result
10
8
6
4
2
00 5 10 15 20 25 30
Surface
improvement
(Crushed stone)
Silty
sand
Clayey
sand
Silty
sand
Clay
Gravely
clay
Clay
Clay
Silt
Dep
th f
rom
th
e s
urf
ace o
f co
ncre
te r
oad
bed
(m
)
N-value
Gravel
N-value must not be
plotted in this area
10
8
6
4
2
00 2 4 6 8 10
10
8
6
4
2
0-300 0 300 600
10
8
6
4
2
00 50 100 150 200
Point resitance q t (MN/m
2) Pore water pressure u
d (kN/m
2) Side surface friction f
s (kN/m
2)
N value Point
resistance Pore water
pressure Side
friction
SPT Electric cone penetration test
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0 1 2 3 4 5 60
50
100
150
Confining pressure 20 kN/m2
Confining pressure 50 kN/m2
Confining pressure 100 kN/m2
Dev
iato
r st
ress
1-
3 (
kN
/m2)
Axial strain (%)1E-5 1E-4 1E-3 0.010
50
100
150
Confining pressure
20 kN/m2
Confining pressure
50 kN/m2
Confining pressure 100 kN/m2
Yo
un
g's
mo
du
lus
Ese
c (
MN
/m2)
Axial strain
Triaxial test
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In-situ cyclic loading test
Vibrationmachine
Reinforced concrete
(Thickness: 300mm)
Subgrade improvement(crushed stone)
Crushed stone layer (150mm)
2400
1,500
Up line
11,840 Unit(mm)
1,500
1,0
00
1,0
00
Down line
Integrated
RC roadbed
Acceleration Earth pressure
Steel stressPore water
Base concrete
(Thickness: 200mm)
Subgrade (clay)
Gauges
Vibration machine
Test site
Integrated RC roadbed
Subgrade
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Loading test results
0 500 1000 1500 20000.0
0.5
1.0
1.5
2.0
2.5Clay subgrade surface
(Just beneath loading point)
2,700 mm distant from loading point
Concrete roadbed surface
(Just beneath loading point)
Accele
rati
on
(m
/s2)
Number of cycles (*1000)
0 500 1000 1500 20000.00
0.05
0.10
0.15
2,700 mm distant from loading point
Dis
pla
cem
en
t (m
m)
Number of cycles (*1000)
Concrete roadbed surface
(Just beneath loading point)
0 500 1000 1500 20000.0
0.5
1.0
1.5
2,700 mm distant from loading point
Edge of concrete base
Rein
forc
ing
ste
el
stre
ss (
N/m
m2)
Number of cycles (*1000)
Just beneath
loading point
0 500 1000 1500 20000
5
10
15
Surface of subgrade improvement
Su
bg
rad
e v
ert
ical
stre
ss (
kN
/m2)
Number of cycles (*1000)
Clay subgrade surface
Acceleration Displacement
Reinforcing steel stress Subgrade vertical stress
120kN, 20Hz, 2x106 times loading
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Reinforced concrete (Integrated RC roadbed)
Clay subgrade
Vibration machine
Well graded crushed stone
-10 -5 0 5 100.20
0.15
0.10
0.05
0.00
-0.05
-0.10 Loading test
FEM analysis
RC
ro
adb
ed d
isp
lace
men
t (m
m)
Longitudinal direction of track (m)
-4 -2 0 2 4-0.5
0.0
0.5
1.0
1.5 Loading test
FEM analysis
Rei
nfo
rcin
g s
teel
str
ess
(N/m
m2)
Transverse direction of track (m)
0
2
4
6
8
10
12
14
2 0 -2 -4 -6 -8 -10
Surface of
clay subgrade
Surface of subgrade
improvement
Loading test
FEM analysis
Depth from RC roadbed surface (m)
Ver
tica
l st
ress
(k
N/m
2)
Displacement Reinforcing steel stress Vertical stress
FEM to simulate the loading test
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Deformation of RC roadbed
Standard RC roadbed Integrated RC roadbed
Integrated RC roadbed distributes train load widely.
Wheel load 85kN Wheel load 85kN
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Standard RC roadbed Integrated RC roadbed
Integrated RC roadbed reduces stress applied on subgrade.
Vertical stress on subgrade
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Integrated RC roadbed
Standard RC roadbed
Integrated / Standard
Vertical displacement
0.60 mm 0.71 mm 0.85
Reinforcing steel stress
2.08 MN/m2 2.33 MN/m2 0.89
Subgrade surface stress
10.5kN/m2 28.6 kN/m2 0.37
Clay subgrade surface stress
6.89 kN/m2 9.02 kN/m2 0.76
Comparison between Standard RC
roadbed and integrated RC roadbed
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Summary
Bearing capacity of roadbed and subgrade is important factor to reduce the maintenance work of ballasted track.
To reduce the settlement of ballasted track at transition zone is an important issue.
Asphalt roadbed is widely applied to ballasted track.
Slab track is widely constructed on the earth structure in these 20 years.
Integrated RC roadbed is a new method to apply slab track on relatively soft subgrade, such as aged diluvial clay.
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