geotechnical issues around ballasted track and slab track ... tc202... · track and slab track in...

Railway Technical Research InstituteRailway Technical Research Institute

Geotechnical issues around ballasted

track and slab track in Japan

Railway Technical Research Institute

Yoshitsugu Momoya

1


Contents

Introduction

Ballasted tracks in existing line

Asphalt roadbed in design standard

Slab track on earth structure

2


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.

3


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

4


Easy to correct track irregularity by tamping.


Good drainage.

5


Apply adequate elasticity on track (especially on bridge or viaduct)


Lateral resistance against lateral train load and rail buckling.

6


Requirement for slab track

Maintenance free.

Not high construction cost.

7


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

8


Heavy rain.

Japan

China

Rain fall in September (average)

Ballasted track after rain

Difficult circumstance for railway track in Japan

Typhoon

9


Contents

Introduction




10


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

11


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

12


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

13


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)

14


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

15


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

16


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

17


Conventional roadbed improvement method:

Crushed stone, steel slag, cement treated material.

Sufficient compaction work was necessary.

Conventional roadbed improvement

18


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.

19


Cyclic loading 5Hz, ΔP=80kN

Sleeper

Ballast

Roadbed

Cyclic loading test

20


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

21


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

22


Before roadbed improvement Excavation of ballasted track

Degraded ballast Preparation of grout

Liquid A

Degraded ballast

Grout material

Liquid B

Application at site

23


Injection of grout

Injection of grout After roadbed improvement

Laying degraded ballast

Application at site

24


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)

25


Concrete

structureEmbankment

Structuraltransition

Generalsection

Concrete structure

Embankment

Floating sleeper

→ large settlement

Structural transition

zone

No floating sleeper

Issues around transition zone

26


Loading actuators

Track model

Scale: 1/5

Embankment

model

Load cells

Concrete

structure

model

Moving loading test

Multi-actuator moving loading test apparatus

27



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

28



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

29


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

30



Concrete slab Low stiffness mat

Concrete approach slab

Approach block (Design standard)

Low stiffness roadbed

Approach block

31


-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


32


Contents

Introduction




33


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.

34


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

35



Asphalt concrete


Subgrade

Displacement at the surface of roadbed

Tensile strain at the bottom of asphalt concrete

Subgrade


Asphalt concrete

Rail Sleeper

Ballast

1/4 symmetric model

36


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


Asphalt concrete


Subgrade

37


・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


38


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)


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

)

39


Contents

Introduction




40


Slab track

鉄道総研 RRR 堀池 2007.6

Rail

Cement asphalt mortar

Slab

Rail Fastener

Concrete trackbed

Circular stopper

41


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

42


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

43


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

44



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

45


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)

46


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



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

47


Co

ncr

ete

ro

adb

ed

Trac

k

CA mortar

Reinforced concrete


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

48


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

49


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)

50


Ground investigation method

Electric cone penetration test Standard penetration test

51


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

52


0 1 2 3 4 5 60

50

100

150

Confining pressure 20 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


Yo

un

g's

mo

du

lus

Ese

c (

MN

/m2)

Axial strain

Triaxial test

53


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


Subgrade

54


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


Accele

rati

on

(m

/s2)

Number of cycles (*1000)

0 500 1000 1500 20000.00

0.05

0.10

0.15


Dis

pla

cem

en

t (m

m)


Concrete roadbed surface


0 500 1000 1500 20000.0

0.5

1.0

1.5


Edge of concrete base

Rein

forc

ing

ste

el

stre

ss (

N/m

m2)


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)


Clay subgrade surface

Acceleration Displacement

Reinforcing steel stress Subgrade vertical stress

120kN, 20Hz, 2x106 times loading

55


Reinforced concrete (Integrated RC roadbed)

Clay subgrade

Vibration machine


-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

56


Deformation of RC roadbed

Standard RC roadbed Integrated RC roadbed

Integrated RC roadbed distributes train load widely.

Wheel load 85kN Wheel load 85kN

57


Standard RC roadbed Integrated RC roadbed

Integrated RC roadbed reduces stress applied on subgrade.

Vertical stress on subgrade

58



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

59


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.

60

geotechnical issues around ballasted track and slab track ... tc202... · track and slab track in...

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