gein20-0316

Reinforcement of railway ballasted track withgeosynthetic bags for preventing derailment

T. Kachi1, M. Kobayashi2, M. Seki3 and J. Koseki4

1Office Manager, Tajimi Track Maintenance Section, CN Const Co., Ltd., 2-75, Taihei-cho, Tajimi-shi,

Gifu, 507-0041, Japan, Telephone: 81/52-451-4509, Telefax: 81/52-451-4913,

E-mail: [email protected] Manager, Mishima Infrastructure Maintenance Depot, Central Japan Railway Company, 3-21,

Ohmiya-cho, Mishima-shi, Shizuoka, 411-0035, Japan, Telephone: 81/55-988-3154,

Telefax: 81/55-987-2417, E-mail: [email protected] Director, Central Japan Railway Company, 1-9-1, Marunouchi, Chiyoda-ku, Tokyo,

100-0005, Japan, Telephone: 81/3-3286-5152, Telefax: 81/3-3286-5165, E-mail: [email protected], Institute of Industrial Science, University of Tokyo, 4-6-1, Komaba, Meguro-ku, Tokyo,

153-0805, Japan, Telephone: 81/3-5452-6421, Telefax: 81/3-5452-6423,

E-mail: [email protected]

Received 9 October 2012, revised 7 June 2013, accepted 2 July 2013

ABSTRACT: In order to prevent a long-term service interruption of Tokaido Shinkansen (bullet

train) in Japan after an earthquake, various structures have been undergoing constant seismic

retrofit. Despite these efforts, a Shinkansen train derailed during the Niigataken-Chuetsu earthquake

in 2004. In order to prevent train derailments, it is important to prevent ballast from collapsing

and flowing out during large earthquakes. Precast concrete blocks are in use on the Tokaido

Shinkansen line for this purpose. However, precast concrete blocks have problems concerning

workability and cost. Therefore, a new method of reinforcing ballasted track has been developed in

which polymeric geomesh bags filled with ballast are stacked and strengthened by reinforcing bars.

The results of shaking table tests confirmed that the reinforced ballasted track has sufficient

seismic resistance against a severe seismic load matching the Tokai earthquake. Several durability

tests were also performed, confirming that bags exposed to ultraviolet radiation for a long time

have sufficient durability. Furthermore, a construction test on a commercial line demonstrated that

the new method provides good workability. Thus the current study demonstrates that the seismic

reinforcement of ballasted track using stacked bags and reinforcing bars is effective and

practicable.

KEYWORDS: Geosynthetics, Ballasted track, Geosynthetic bags, Seismic resistance, Shaking table

tests.

REFERENCE: Kachi, T., Kobayashi, M., Seki, M. & Koseki, J. (2013). Reinforcement of railway

ballasted track with geosynthetic bags for preventing derailment. Geosynthetics International, 20, No. 5,

316331. [http://dx.doi.org/10.1680/gein.13.00023]

1. INTRODUCTION

In order to prevent a long-term service interruption of the

Tokaido Shinkansen (bullet train) after an earthquake,

seismic retrofit of structures, such as embankments and

steel bridges, has been carried out continually for many

years.

On 23 October 2004, a near-fault type earthquake

struck the Chuetsu region in Niigata Prefecture, and a

Joetsu Shinkansen train travelling at 200 km/h derailed.

On conventional lines, track ballast collapsed and flowed

out in some locations during the earthquake, causing

severe track settlement.

Track structure for the newer Shinkansens, for example

Joetsu Shinkansen, is almost all slab track. Nevertheless

the Tokaido Shinkansen track is seated mostly on ballasted

structures. However, a seismic design manual for ballasted

track structures is not available, because ballast behaviour

is not fully understood. As part of the measures to address

train derailment concerns for Shinkansen ballasted track

(Morimura and Seki 2009), the present study focuses on

the shoulder ballast of conventional ballasted track that

may severely deform during a large earthquake, causing

large settlement. Track panels comprising rail and tie need

to be supported by ballast not only vertically but also

Geosynthetics International, 2013, 20, No. 5

3161072-6349 # 2013 Thomas Telford Ltd

horizontally. Nevertheless when the ballast collapses and

flows out during large earthquakes, the lateral ballast

resistance force is reduced. Consequently, large track

misalignment may be triggered. Results from past shaking

table tests have revealed such failure mechanisms (Iwata

and Iemura 2003). In order to prevent ballast collapse,

flow-out and to minimise track irregularity, it is important

to construct a retaining wall structure on the outside of the

ballasted track, which can restrain ballast from displace-

ment. With this in mind, the authors developed a new

method of reinforcing a ballasted track using geosynthetic

bags manufactured from a geomesh product. The purpose

of this study was to verify the effectiveness and practic-

ability of the method as a seismic measure to prevent

additional damage by train derailment during earthquakes.

There have been several attempts to reinforce ballasted

structures using sheet geosynthetics (e.g. Chen et al.

(2012), Ferellec and McDowell (2012) and Leshchinsky

and Ling (2013)). To the authorsbest knowledge, no

research has been conducted to date on the use of ballast-

filled geosynthetic bags for seismic damage mitigation on

rail track support.

2. GEOSYNTHETIC BAG METHOD

The current method employed in Japan to prevent ballast

collapse and flow-out during large earthquakes is to add

precast concrete blocks to the ballasted track (Ikegami et

al. 1982; Figure 1). An example is the track structure of

Tokaido Shinkansen. The effectiveness of this measure has

been confirmed (Nagao et al. 2006). The precast concrete

blocks have a projection on the bottom face. Sufficient

horizontal bearing capacity is ensured by this projection

when it is dug into the roadbed. Moreover, the bottom

face resists overturning.

However, the precast concrete blocks are 500 mm wide

and weigh approximately 200 kg. Construction using pre-

cast concrete blocks therefore needs heavy equipment and

closure of the railroad track, which hampers early comple-

tion of construction and raises construction costs. The

construction on the back side of the block needs great

care, because insufficient tamping can result in large

horizontal displacement during large earthquakes.

In seeking a new ballasted track structure that is super-

ior to precast concrete blocks with respect to economy and

workability, the authors initially focused on the reinforced-

soil retaining wall method with full-height rigid facing

(Tatsuoka et al. 1997; RTRI 2007; Figure 2). This method

involves stacking bags at a stable, near-vertical angle. The

concrete facing is then constructed against the front of the

stacked bags to further enhance stability. However, even

before the facing is constructed, the stacked bags them-

selves form a stable retaining wall.

The authors also focused on the sandbag method

(Matsuoka 2003; Matsuoka and Liu 2003) in which

sandbags are employed to construct a retaining wall to

stabilise a potentially collapsible slope. When a sandbag is

subjected to an external load, a tensile force is generated

around the bag, which adds an apparent cohesion, enhan-

cing the bearing capacity of the bag (Figure 3). The bags

themselves are cheap and easy to procure. Moreover, since

it is easy to adjust their weight simply by changing their

size and they can be stacked up, the retaining wall can be

constructed manually. The sandbag method is therefore

more economical and efficient for construction. Such

sandbags are also employed for emergency measures in

river protection works (Brandl (2011) among others) and

for reinforcement of earth fill dams (Mohri et al. 2009).

Ballast has large particle size and many edges. The

large frictional resistance generated between mutually

engaged ballast particles stabilises the ballasted track

against railway vibration. With a retaining wall of conven-

tional sandbags filled with ballast, there was the possibi-

lity that adequate frictional resistance would not be

generated at the boundary between two bags.

Figure 4 shows a newly proposed method to reinforce

ballasted track (basic configuration, Kachi et al. 2010).

The proposed structure is composed of stacked geosyn-

ProjectionConcrete block

Figure 1. Concrete blocks for reducing deformation of

ballasted track

Rigid facing Sand bag

Geotextile

Figure 2. Reinforced-soil retaining wall

c

No bags

With bags

External force

Tension

Figure 3. Effect of wrapping bags on base shear resistance

(after Matsuoka 2003)

Reinforcement of railway ballasted track with geosynthetic bags for preventing derailment 317


thetic bags filled with ballast and steel bars driven into the

roadbed to increase the shear resistance of the stacked

bags and to reinforce them. The bags are made from high

durability geomesh so that the frictional resistance can be

developed between the ballast in adjacent bags. Recycled

ballast may be used to fill the bags. As the weight of each

bag can be easily adjusted by changing its size, the bags

can be stacked manually. Moreover, execution of this

proposed method does not require any special construction

equipment or closure of the railway track. This method is

therefore more economical and efficient than the precast

concrete block method. In addition, it is expected that this

reinforced ballasted track method will also reduce rail

buckling, roadbed caving and track deformation.

3. HORIZONTAL BEARING CAPACITYTESTS OF BASIC CONFIGURATION

In order to examine the basic configuration of the

reinforced ballasted track, horizontal load tests were

performed on several types of ballasted structure. As

shown in the schematic of Figure 5, a horizontal load was

applied through a hydraulic actuator to the ballast cover of

each test structure (Kachi et al. 2009, 2010). A load cell

and a laser displacement transducer were used to measure

the horizontal load and horizontal displacement, respec-

tively. The test was conducted three times for each test

structure. The load was applied at the height of one-third

from the bottom, while assuming that the corresponding

earth pressure distribution would be hydrostatic.

Figure 6 shows three configurations (precast concrete

blocks, stacked bags, stacked bags with reinforcing bars)

for the horizontal bearing capacity tests and Figure 7

shows the results. The vertical axis represents the horizon-

tal displacement measured at the top layer of stacked bags

that resulted from the uniform horizontal load. The

shearing force at the base of the bag was measured with a

load cell in the shaking table model tests series that are

described later. The result of the shaking table tests

showed that the greatest value of the shearing force was

Geosynthetic bags

Reinforcing steel bars

Figure 4. Ballasted track reinforced with geosynthetic bags

Unit: mm

Ballast cover

Supporter

Simulated embankment

Test structure

Load cell Hydraulic actuator

Measurement ofdisplacement

400

About 600

About350

About 1200

Figure 5. Horizontal bearing capacity test

500500 500

200

860

Concrete blocks

400

Stacked bags

400 200Unit: mm

Stacked bags withreinforcing bars

Figure 6. Model configurations in horizontal bearing capacity tests

318 Kachi, Kobayashi, Seki and Koseki


1.0 kN. Therefore, the horizontal load that was applied to

the stacked bags was assumed to be on the order of

1.0 kN. Figure 7 shows that the horizontal displacements

of the stacked bags due to horizontal loads in the range of

0.53.0 kN were in general larger than those for the

configurations with precast concrete blocks. On the other

hand, by adding the reinforcing bars to the stacked bags,

the horizontal displacements could be reduced signifi-

cantly. This provides an alternative solution that is equiva-

lent to or even better than using precast concrete blocks.

4. SHAKING TABLE MODEL TESTS ONBASIC CONFIGURATIONS

In order to confirm the dynamic response of reinforced

ballasted track subjected to high seismic loads, an initial

series of shaking table tests was performed on full-scale

models (Kachi et al. 2009, 2010).

4.1. Test models and procedures

Figure 8 shows an example of the test models. Full-scale

models of a half section of a double track were con-

structed in a rigid steel box on a shaking table. The steel

box was partitioned into two spaces, enabling two different

models to be excited at the same time. In order to reduce

the forces from the steel box, two urethane foam mat-

tresses with nominal compressive strengths of 16.5 and

78.4 N/cm2, and thickness of 100 mm were inserted be-

tween the test structure and the steel box. A round steel

bar having a diameter of 12 mm with a smooth surface

was driven into the roadbed to a depth of 200 mm. The

bags, with 25 mm mesh openings, were made of polyester.

Each bag was filled with 25 kg of ballast and compacted

into a size of 400 mm long by 400 mm wide by 100 mm

high with a plate compacter. The roadbed was prepared by

compacting a sandy soil to a wet unit weight t of17.0 kN/m3: Table 1 shows a description of the ballast androadbed materials. The model track materials and rail are

typical for the Tokaido Shinkansen.

The input motion for the shaking table tests was the

response acceleration at the top of a track-supporting

embankment obtained by finite element (FE) dynamic

analysis matching the anticipated Tokai earthquake motion

(Matsuda et al. 2009). This input motion is much more

severe than the so-called Level 2 earthquake motion

prescribed for railway structures (RTRI 1999), and has

unfavourable characteristics for an embankment, namely a

long shaking duration and a long period of shaking. Figure

9 shows the input motion for the shaking table tests and

its Fourier spectrum.

4.2. Selection of performance criteria

In the present study, to numerically evaluate the seismic

performance of the reinforced ballasted track, two target

performance criteria were established.

The first target value is the maximum tie displacement

in the shaking table test. The established target is 25 mm

or less. There are two reasons for this value. The first is

that a shaking table test was performed using a real train

bogie in a related experiment (Muramatsu et al. 2009)

3.02.52.01.51.00.5

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t the

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ofst

acke

d ba

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)

Horizontal bearing capacity (kN)

Concrete blocks

Stacked bags

Stacked bags with reinforcing bars

Figure 7. Results of the horizontal bearing capacity tests

1600

600

6400

2900 2400 900 200

300

400

Unit: mm

1600

Figure 8. Shaking table model tests on basic test

configurations

Table 1. Test material for shaking table tests

Material

Roadbed Mountain sand of Iwase, Ibaraki Prefecture

Ballast Crushed stone ballast for railway (2060 mm)



using the input motion for the Tokai earthquake. For the

conditions in which the guard rail fulfilled its function,

the maximum tie displacement was 27 mm. The other

reason is that 25 mm is the accepted maximum displace-

ment criterion (Yoshida et al. 2009).

The second target value is related to the lateral ballast

resistance force, which is considered to have a significant

influence on the stability and buckling of the track even

after an earthquake. The established criterion for this

resistance force is 10.8 kN per tie at a tie movement of

3 mm, which is the standard control value for the lateral

ballast resistance force (Tanaka and Isoura 1998). Despite

0

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Original design ground motion

Responsive wave at the top ofthe embankment

Standard wave on theshaking table

Original design ground motion (gal)

Response wave at the top of the embankment

Standard wave on the shaking table

1000

1500

1000

1500

max 1377.6min 966.6

1000

1500

Figure 9. Input motion for the shaking table tests and its Fourier spectrum



a low probability of very high temperature occurring

simultaneously with a large earthquake, this control value

was used for this worst-case scenario.

4.3. Test results

Figure 10 shows the test result using precast concrete

blocks (case 1). The maximum horizontal displacement of

the top block was 16 mm, and that of the tie was 21 mm,

therefore the first criterion was satisfied. The horizontal

displacement of the bottom block was similar to the value

for the top block. This indicates that a sliding failure

mode along the foundation base was predominant. In this

case, the permanent settlement of the tie (hereafter cited

as P.s.t in the figures) was 5.7 mm.

Figure 11 shows the test result for the basic configura-

tion (case 2). The maximum horizontal displacement of

the top layer of stacked bags was 19 mm, and that of the

tie was 21 mm, therefore the first criterion was satisfied.

The horizontal displacement of the bottom layer of

stacked bags was much smaller than the value for the top

layer. This indicates that the reinforced ballasted track

suffered an overturning mode of displacement, rather than

a sliding mode along the base foundation.

Figure 12 shows the test result for the basic configura-

tion with larger track shoulder width (case 3). The maxi-

mum horizontal displacement of the top layer of stacked

bags was 42 mm, and that of the tie was 40 mm, therefore,

the first criterion was not satisfied. Two possible reasons

can be considered for this response. One is that the

dynamic earth pressure acting on the geosynthetic bags

was increased, due to larger ballast profile area. The other

reason is that the single bag in the second line has large

deformation because of the limited amount of overburden

pressure due to the self-weight of the bag and the absence

of steel bars to reinforce the bag. Therefore, it was

necessary to improve the proposed basic configurations.

The permanent settlements of the tie (P.s.t) were 10.6

and 20.3 mm for cases 2 and 3, respectively. Although

these values were larger than the value observed in case 1,

it could be confirmed that the permanent settlements with

the proposed method remain within an allowable range.

Figure 13 shows the lateral ballast resistance force

measured after the shaking table tests. The lateral ballast

resistance force for case 2 and case 3 models measured

after the shaking table tests was less than 10.8 kN at a tie

movement of 3 mm. Hence, these cases did not satisfy the

second criterion described in the previous section. There-

fore, further improvement was required from this view-

point as well.

5. HORIZONTAL BEARING CAPACITYTESTS ON IMPROVEDCONFIGURATIONS

In order to reduce the maximum horizontal displacement,

it was necessary to modify the basic configuration of the

reinforced ballasted track. Additional horizontal loading

tests were therefore performed on several types of

ballasted structure.

5.1. Test procedures

The test procedures are similar to those shown in Figure

5. Table 2 and Figure 14 show the test cases. Case (a) is

the basic configuration. In case (b), to enhance the passive

resistance of the reinforcing steel bars driven into the

roadbed, the depth of the reinforcing steel bars was

500

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25201510

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P.s.t 5.7 mm

Bottom of the block -- of the blockTop -- Tie

5040302010

500

500300

218

0

Tie

Bottom

Top

Maximum horizontal displacement (mm)Cross-section: units are mm

5

1000

1500

Figure 10. Results of concrete block test (case 1)



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Bottom of the bags -- Top of the bags -- Tie

Cross-section: units are mm

50403020100

Tie

Bottom

Top

Maximum horizontal displacement (mm)

10040080

100

200

820

10001500

Figure 11. Results of reinforced bag test (case 2)

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5040302010

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100

200

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Cross-section: units are mm

0

Tie

Bottom

Top

Maximum horizontal displacement (mm)

1000

1500

Figure 12. Results of reinforced bag test (case 3)



increased from 200 mm to 300 mm. Based on a related

earlier study that showed that the shear resistance of an

inclined stack of bags is much larger than that of a

horizontal stack of bags (Matsushima et al. 2008), the

proposed method was modified in case (c) by stacking the

bags at an inclination angle of 22.58, while driving thereinforcing steel bars vertically. In case (d), to resist

overturning of the stacked bags in a more effective

manner, the reinforcing steel bars were driven at an angle

of 708 to the vertical. By doing so, the upper three layersof bags alone were interconnected by the bars. In case (e),

therefore, additional steel bars were driven to interconnect

the lower three layers of bags as well.

5.2. Test results

Figure 15 summarises the test results in terms of the

horizontal displacements at the top of the stacked bags,

which were induced at horizontal loads in the range of

0.53.0 kN. It can be seen that the horizontal bearing

capacity was improved by increasing the embedment depth

of the reinforcing bars, by stacking the bags and driving

the reinforcing bars at an angle, and by increasing the

13121110987654321

10.8

6.4

8.6

11.5

0

Case 3

Case 2

Case 1

Lateral ballast resistance force at tie movement of 3 mm (kN)

Figure 13. Results of lateral ballast resistance force tests

Table 2. Shaking table test configurations

Case Method of stacking

bags

Inclination angle of

stacked bags

Depth of the

reinforcing steel bars

Number of bars in

each cross-section

a Level 908 200 mm 1

b Level 908 300 mm 1

c Inclination 708 300 mm 1

d Inclination 708 300 mm 1

e Inclination 708 300 mm 2

300

50

461 370

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400

400

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461

22.5

400

70300

370

300

50

461 370

22.5

Case (a) stacking bags withlevel, 90, 200 mm

Case (b) stacking bags withlevel, 90, 300 mm

Case (c) stacking bags withinclination, 90, 300 mm

Case (b) stacking bags with, 70, 300 mminclination

Case (e) stacking bags with, 70 2, 300 mminclination

Figure 14. Model configurations for the horizontal bearing capacity tests



number of the reinforcing bars per running length of

section. At the same horizontal load, the horizontal

displacement for case (e) that employed all of the above-

mentioned modifications was about a quarter of that for

case (a). This particular configuration exhibited superior

performance even when compared to the precast concrete

blocks (case 1) shown in Figure 7.

Figure 16 summarises the improvements made based on

the results of the horizontal bearing capacity tests. It is

expected that stacking the bags at a slope would improve

their capacity against dynamic earth pressure, which

would be further enhanced by the addition of inclined

reinforcing bars that mobilises the tensile resistance of the

bars. Increasing the embedment depth of the reinforcing

bars and increasing the frequency of reinforcing bars

would also help in securing sufficient tensile resistance. In

the following section, a model which is similar to case (e),

which had the best performance, is investigated as an

improved configuration for reinforced ballasted track.

6. SHAKING TABLE MODEL TESTS ONIMPROVED CONFIGURATION

In order to confirm the seismic resistance of the improved

configuration of the reinforced ballasted track with larger

track shoulder width, a second series of shaking table tests

was performed (Kachi et al. 2009, 2010; and Koseki

2012).

6.1. Test model and test procedures

Figure 17 shows a test model. Due to the limited capacity

of the shaking table employed for the second series of

tests, one model was constructed in a smaller rigid steel

box and excited. In order to reduce friction, the inside of

the steel box was coated with Teflon spray. The roadbed

was prepared by compacting a sandy soil to a wet unit

weight t of 17.0 kN/m3: The test procedures are similarto those shown in Figure 8. In order to enhance passive

resistance of the reinforcing steel bars, deformed steel bars

having a rough surface and a nominal diameter of 13 mm

(used to reinforce concrete) were driven into the roadbed

to a depth of 300 mm.

The test model employed U-shaped reinforcing steel

bars to enhance the overall stiffness of the stacked bags,

which were produced by welding two reinforcing steel

bars and a short steel bar together. There are two reasons

for employing the U-shaped bars. One is that U-shaped

bars induce an additional overburden load by stapling the

top of the stacked bags. Another reason is that a U-shaped

bar connects a bag with an adjacent bag in the direction

parallel to the rails. It should be noted that the tensile

force in the steel bars was measured with strain gauges

attached to straight bars, because instrumented deformed

steel bars could not be welded.

The input motion for the second series of the shaking

table tests matched the Tokai earthquake.

6.2. Test results

Figure 18 shows the result of the shaking table test on the

improved configuration (case 4). The maximum horizontal

displacement of the top layer of stacked bags was 9 mm

and that of the tie was 6 mm. Therefore, this maximum

4.03.02.01.00

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acke

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a

b

c

d

e

Figure 15. Results of horizontal bearing capacity tests

1 2

22.5

70

Improvement

Stackingbags

LevelInclination(22.5)

Bar Degrees 9070Inclination

Depth 200 mm 300 mm

Number

OthersSize of the bag: 400 400 100 mm Polyester mesh: 25 mmReinforcing bars: nominal diameter (13 mm)

Item

Figure 16. Shaking table model tests with improved stacked

bag configurations

1600

1280 1220 2400 900 200

1000

350

300

6000Unit: mm

Figure 17. Shaking table model tests of improved model

configurations



horizontal displacement of the tie is smaller than the first

target value (25 mm). This result proves that the improved

configuration of the reinforced ballasted track, which

employed stacked bags and inclined reinforcing bars,

exhibited sufficient seismic resistance even under a wider-

track condition.

To improve economy and workability, a reinforced

ballasted track using one reinforcing steel bar per bag was

investigated as another improved configuration (case 5).

Figure 19 shows the results of the shaking table test on

this improved configuration (case 5). The maximum

horizontal displacement of the top layer of stacked bags

was 14 mm, and that of the tie was 7 mm. Thus the

maximum horizontal displacement at the tie is smaller

than the aforementioned target value (25 mm). It can be

noted that the permanent settlement of the tie (P.s.t) was

1.2 mm. Figure 20 shows the relationship between the

horizontal displacement of tie and the horizontal accelera-

tion of the shaking table test. As indicated by the dashed

lines and a horizontal arrow, when the acceleration

exceeded a threshold value of about 1000 gal (1g), large

residual horizontal displacement of the tie accumulated.

On the other hand, when the acceleration remained within

the threshold value, the horizontal displacement of the tie

could be restored.

Figure 21 shows the lateral ballast resistance force

measured after the shaking table tests of cases 4 and 5.

The lateral ballast resistance force of these improved

configurations measured after shaking was 10.8 kN or

more at movement of 3 mm. That is to say, both improved

configurations (cases 4 and 5) satisfy the two displace-

ment criteria. This result confirms that the two improved

configurations have sufficient seismic resistance. The im-

proved configuration (case 5) was adopted as the standard

reinforced ballasted track structure.

7. PERFORMANCE EVALUATION TESTSFOR THE BAG

As has been noted, the reinforced ballasted track has a

sufficient seismic resistance and is feasible for practical

use. To confirm the durability of geosynthetic bags,

several performance evaluation tests were performed on

the bags (Kobayashi et al. 2009).

7.1. Cutting resistance tests for bag material

In the construction of the reinforced ballasted track, the

bags are filled with ballast and stacked up in layers while

being compacted with a plate compactor. During compac-

tion, the polymeric strands of each geomesh bag that are

caught between ballast and plate compactor can be broken

(cut). Breakage of several strands per bag is permissible,

but it is necessary to avoid severe damage to the bags. In

situ cutting resistance tests were therefore performed on

candidate geosynthetic bag materials.

The cutting tests were performed on horizontal sheets

of the geomesh materials, as shown in Figure 22. The test

sheets were laid on a simulated embankment, then ten-

sioned and fixed with anchors. The sheets were then

compacted by running a plate compactor (mass: 45 kg) ten


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m)

Time (s)

P.s.t 1.2 mm

400 370400100

50

22.5

1330

70 300

50 50 50 Top

Bottom

Tie

0 10 20 30 40 50

Maximum horizontal displcementCross-section: units are mm

1000

1500

Figure 18. Results of shaking table model test with improved configuration (case 4)



times in the longitudinal and cross directions to simulate

the actual construction. The tension applied to the material

was measured with a spring scale and adjusted to 68.6 N

per anchor. The number of breaks in each sheet was

counted. The percentage of broken strands for different

materials was compared.

The test materials are listed in Table 3. These materials

were selected based on cost and availability. These geomesh

materials have 2030 mm aperture sizes. The constituent

materials were polyester, polyethylene, and polyethylene-

coated polyester and are used in the manufacture of various

types of geomesh. Vinylon and polyarylate are the polymers

used in reinforcing sheet materials in the reinforced railroad

with rigid facing-method (RRR) (Tamura 2006).

Figure 23 shows the test results as the average of three

measurements. The results are in terms of percentage of


500

0

500

1000

1500

Inpu

tac

cele

ratio

n(g

al)

252015105

05

10

0 5 10 15 20 25 30 35

Hor

izon

tal

disp

lace

men

t(m

m)

Time (s)

P.s.t 1.2 mm

400 370 400100

22.5

1330

70 300

50 50 50Top

Bottom

Tie

0 10 20 30 40 50

Maximum horizontal displcementCross-section: units are mm

1000

1500

Figure 19. Results of shaking table model test for another improved configuration (case 5)

5000

500100015002000

0 5 10 15 20 25 30 35

Inpu

tac

cele

ratio

n (g

al)

Time (s)

500

0

500

1000

1500

8 6 4 2 0 2 4

Inpu

tac

cele

ratio

n (g

al)

Horizontal displacement (mm)

10001500

1000

1500

Figure 20. Relationship between horizontal displacement of tie and acceleration of the input motion in the shaking table test



broken strands, since the materials have different numbers

of strands. The poorest material with respect to breakage

was polyester, and best material was polyethylene-coated

polyester. Nevertheless, polyethylene was selected as the

main material for the geosynthetic bags, because of cost

and availability.

7.2. Cutting resistance tests on selected bag

materials

Next, cutting resistance tests were performed under simu-

lated construction conditions. In preparing test samples,

polyethylene was combined with about 10% polyarylate to

provide an economical improvement in breakage durabil-

ity. Polyarylate has more than four times greater cutting

resistance than polyethylene. For this reason polyarylate is

used to manufacture fishing nets, protective nets and

industrial safety gloves.

Test materials are listed in Table 4. For one of the tested

materials, the strands were manufactured using raschel

netting in a diamond mesh pattern due to its cutting

resistance and ease of manufacture. The strands were

knitted so that polyarylate with high cutting resistance was

exposed on the surface. Each intersection of strands where

strand breakage would result in a large opening was

reinforced by increasing the strand overlap length.

Three bags filled with ballast (mass: 25 kg/bag, size:

400 mm long by 400 mm wide by 100 mm high) were

prepared for each test material. The bags were laid on a

simulated embankment and compacted by running a plate

compactor (mass: 45 kg) over the bags in longitudinal and

cross directions as before. The number of breaks (N) was

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16Lateral ballast resistance force (kN/unit)

Case 4

Case 5

3 mm

10.8

14.6

13.7

Figure 21. Results of the lateral ballast resistance force tests

Spring scaleTurn buckle

Test piece

0.5

m

Anchor

Figure 22. Cutting resistance test using geomesh sheets

Table 3. Cutting resistance test geomesh sheet materials

No Test material Aperture size Knitting Thickness

1 Polyester 25 mm Raschel 2 mm

2 Polyethylene 25 mm Without knot 2 mm

3 Vinylon 20 mm Grid W: 5 mm, T: 1 mm

4 Polyarylate 20 mm Grid W: 5 mm, T: 1 mm

5 Polyester (with polyethylene film) 35 mm Without knot 4 mm

W, width; T, thickness.

0

1

2

3

4

5

6

7

8

9

10

Bre

akin

g pe

rcen

tage

9.3

1.3

2.7

0.60

Polyester Polyethylene Vinylon Polyarylate Polyester(with

polyethylenefilm)

Figure 23. Cutting resistance test results for geomesh sheets

Table 4. Materials for cutting resistance strength tests

No Test material Mesh size Knitting Thickness

1 Polyethylene 25 mm Without knot 2 mm

2 Polyethylene + polyarylate 25 mm Raschel 2 mm



counted to evaluate the cut resistance. However, to make

the difference in cut resistance easier to detect, the plate

compactor was run 50 times both ways (Figure 24).

Figure 25 shows the test results in terms of the number

of breaks. The test results are the average of number of

cuts from three samples of each material. Polyarylate-

combined polyethylene was superior in cut resistance to

polyethylene alone, confirming the effectiveness of com-

bining it with polyarylate. On actual construction sites, the

number of breaks of each bag would be fewer since a

plate compactor is run only three times both ways.

In view of the above results, polyarylate-combined

polyethylene was selected as the bag material.

7.3. Ultraviolet light resistance tests on bag material

Like many polymers, polyethylene and polyarylate are

susceptible to degradation due to ultraviolet radiation

(sunlight). Therefore, carbon black or another ultraviolet-

absorptive agent is mixed with the constitutive polymer. If

the bags are used to prevent ballast from flowing out of

reinforced ballasted track, the surface of the bags should

be covered with ballast as much as possible to prevent

direct exposure to sunlight. However, it may be difficult to

cover the surface with ballast depending on the field

circumstances. Therefore, the ultraviolet light resistance of

the bags was investigated by testing.

Accelerated exposure weathering tests were performed

in accordance with JIS L1096 (General cloths tests) 6.30.1

(JISC 2010b). A super xenon weather meter was used for

the test because its wavelength content is similar to that of

sunlight and it is possible to shorten the test period. Table

5 shows the test conditions.

In order to confirm the ultraviolet resistance, five

samples were exposed to ultraviolet radiation for the

specified duration and then subjected to tensile strength

testing conducted in accordance with JIS L 1013 (JISC

2010a).

The test materials are listed in Table 6; polyarylate-

combined polyethylene and also single polyethylene mate-

rials were tested.

Figure 26 shows the results of the tensile strength tests

conducted after accelerated radiation exposure tests. The

results are the average of five samples. The tensile

strength of polyarylate-combined polyethylene increased

for some time after the start of ultraviolet irradiation.

There are two reasons for this phenomenon. One reason is

the increase in polyethylene crystallinity. The other reason

is that the number of polymer chain crosslink scissions

caused by the ultraviolet light was larger than that of the

molecular chain breaks (e.g. Osawa and Narusawa 2002).

Material 1 3 Material 2 3

1 Polyethylene 2 Polyethylene polyarylate

Figure 24. Cutting resistance tests on filled bags

Polyethylene polyarylate

18.0

10.3

0

5.0

10.0

15.0

20.0

Polyethylene

Num

ber

of

brea

ks

Figure 25. Results of cutting tests on filled bags

Table 5. Ultraviolet radiation resistance test conditions

Item Contents

Testing apparatus Super xenon weather meter

Temperature of the panel 638C 18CSpraying time 18 min (in 1 cycle of 120 min)

Emission illuminance 180 W/m2

Irradiation time 250, 500, 1000, 2000, 3000, 5000 h

Table 6. Test materials for ultraviolet radiation resistance tests

No Material Color Thickness Protective additive

1 Polyarylate-combined polyethylene Black 2 mm Ultraviolet radiation absorptive agent

2 Polyethylene Green 2 mm None



With further increase in irradiation time, the tensile

strength decreased. This is because of progress in mole-

cular chain breakage caused by ultraviolet light.

As shown in Figure 26, the loss of tensile strength

declined after an irradiation time of 3000 h. In regard to

the relationship between the irradiation time by a super

xenon weather meter and the real sunshine time, it is

reported that the average energy of ultraviolet sunlight in

a year (300400 nm) is equivalent to approximately

300 MJ/m2 (Japan Weathering Test Center 2004). There-

fore, 500 h of irradiation by the super xenon weather

meter corresponds to 1-year exposure to sunlight. Based

on the test results obtained thus far, it can be concluded

that the test material maintains approximately 60% of its

initial tensile strength even after 5000 h of ultraviolet

irradiation, or exposure to sunlight for 10 years.

According to the mechanism of material deterioration

by ultraviolet light, an oxide layer is formed on the surface

of the fibre as the irradiation time increases. It is generally

believed that this oxide layer prevents ultraviolet radiation

from penetrating the polyethylene thereby mitigating

deterioration caused by sunlight. This mechanism may

have affected the above test results.

From the data obtained after 250 h of irradiation, an

approximate equation expressed as an index function can

be obtained. Figure 26 shows the approximate equation.

After extrapolation, a tensile strength of not less than

50 N/unit after 10 000 h of irradiation was obtained. This

means that polyarylate-combined polyethylene has suffi-

cient retained strength.

The above-mentioned test results indicate that

polyarylate-combined polyethylene bags can maintain

their design function for a sufficient period of time when

exposed to ultraviolet light.

No severe deterioration was observed in the polyethylene-

based geosynthetic materials in the ultraviolet resistance

tests performed in the past (e.g. Harada and Kato 2004). In

future, it is recommended to carry out weathering tests of

the bags at actual sites to evaluate their durability under

operational conditions.

8. FIELD CONSTRUCTION TEST

It has been confirmed that the standard configuration of

reinforced ballasted track has sufficient seismic load

resistance. However, it was anticipated that stacking bags

at an angle and driving inclined reinforcing steel bars

through them could affect the workability. To confirm the

workability of the reinforced ballasted track, a field

construction test was performed on a commercial line.

Figure 27 shows schematic views of the reinforced

ballasted track test. The test section was built adjacent to

the outside rail of a 10 m-long curved section of track

with a radius of 2500 m and a cant (cross fall) of 200 mm.

To accommodate the cant, the reinforced ballasted track

was constructed with six layers of bags. With regard to the

workability, the labourers quickly became proficient at

stacking the bags at an angle and tamping the bags with a

plate compactor.

To facilitate the driving of reinforcing steel bars at an

inclination, a jig was manufactured and placed on the head

of the reinforcing steel bar before it was driven in. The

angle of driving of each steel bar was measured with a

goniometer (protractor). An electric hammer was used to

drive the reinforcing steel bars. Where ballast with large

particle size was encountered in the bags or where the

roadbed soil was consolidated, the driving of the reinfor-

cing steel bars took longer. However, driving the reinfor-

cing bars at an inclination did not present any difficulties.

Figure 28 shows the construction work progress charts

using manual labour and a backhoe. Construction using

manual labour for the 10 m-long section did not take

longer than 4 h. Thus, it was confirmed that the reinforced

ballasted track can be constructed much more easily than

using precast concrete blocks.

100008000600040002000

yR287.0e

0.93

0.0001

2

x

0

50

100

150

200

250

300

350

0

Tensi

le s

trength

(N/u

nit)

y

Accelerated exposure weathering time (h)x

Polyarylate-combined polyethylene

Polyethylene

Figure 26. Results of the tension strength tests after

ultraviolet radiation resistance testing

300

1350

300

650

Original cross-section

700

746

22.5

50

500539

400 204

Unit: mm

50 50

70

Figure 27. Cross-section and plan view of construction test



Track maintenance work tests were also performed at

the test section, to investigate the influence of stacked

bags on the track maintenance work, such as ballast

renewal, tie renewal, and rail renewal which requires

welding work. Stacked bags close to the track ties may

interfere with track maintenance. However, this problem

can be solved by temporarily removing the bags and

restoring them after track maintenance work is completed.

Thus, it was confirmed that reinforced ballasted track

using the geosynthetic bag method proposed in this study

will not negatively impact track maintenance activities.

9. CONCLUSIONS

The results from the present study are summarised in the

following list.

(1) A reasonable and economical geosynthetic bag

method to reinforce ballasted track is proposed. This

method involves stacking up ballast-filled geosyn-

thetic bags and driving steel bars into the roadbed to

increase the shear resistance of the bags and to

reinforce the bags.

(2) Comparisons between the results of full-scale

shaking table model tests and performance criteria

confirmed that the reinforced ballasted track

composed of inclined stacks of geosynthetic bags

and reinforcing steel bars driven at an angle have

sufficient seismic resistance.

(3) The results of ultraviolet radiation tests showed that

the bags have sufficient durability when exposed to

sunlight for a long time.

(4) A field construction test at an actual commercial line

site confirmed that the geosynthetic bag method is

practical from a workability point of view.

Future studies are recommended to assess the long-term

performance of the proposed method under working load

conditions, including possible changes in the resonance

frequency of the ballasted track.

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Brandl, H. (2011). Geosynthetics applications for the mitigation of

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modelling of cyclic loads of geogrid-reinforced ballast under

confined and unconfined conditions. Geotextiles and Geomem-

branes, 35, 7686.

Ferellec, J. F. & McDowell, G. R. (2012). Modelling of ballastgeogrid

interaction using the discrete-element method. Geosynthetics

International, 19, No. 6, 470479.

Harada, M. & Kato, H. (2004). Durability Evaluation of Fibrous Rope,

Aichi Industrial Technology Institute Report, Aichi Center for

Industry and Science Technology, Toyota, Japan (in Japanese).

Ikegami, K., Ieda, H., Hanawa, S. & Jinno, K. (1982). Efficiency test and

design of the ballast curb blocks. Railroad Track, 30, No. 8, 461

466 (in Japanese).

Iwata, S. & Iemura, H. (2003). Seismic limit performance of ballast track

structure by large-scale strong earthquake response simulator test.

Proceedings of the Annual Conference of the Japan Society of Civil

Engineers, Tokushima, Japan, September 2003, 58, 6566 (in

Japanese).

JapanWeathering Test Center (2004).Measurement Table of Environmental

Factor, Japan Weathering Test Center, Tokyo, Japan (in Japanese).

JISC (Japan Industrial Standards Committee) (2010a). JIS L1013: Testing

Methods for Man-made Filament Yarns. Japan Industrial Standards

Committee, Tokyo, Japan (in Japanese).

JISC (2010b). JIS L1096: Testing Methods for Woven and Knitted

Fabrics. Japan Industrial Standards Committee, Tokyo, Japan (in

Japanese).

Kachi, T., Seki, M., Kobayashi, M., Nagao, T. & Koseki, J. (2009).

Measures for preventing derailment and dislodgement on Tokaido

Shinkansen applied ballasted track reinforced with geosynthetic

bags. The 16th Jointed Railway Technology Symposium 2009,

Tokyo, Japan, December 2009, pp. 647650 (in Japanese).

Kachi, T., Kobayashi, M., Seki, M. & Koseki, J. (2010). Evaluation tests

of ballasted track reinforced with geosynthetic bags. Proceedings of

the 9th International Conference on Geosynthetics, Brazil, pp.

14991502.

Kobayashi, M., Watanabe, Y., Yoroisaka, K. & Muramatsu, H. (2009).

Performance evaluation tests and construction tests of ballasted

track reinforced with geosynthetic bags. The 16th Jointed Railway

Excavating ballasts

Avoiding maintenance car

Packing ballasts in the bags

Excavating with backhoe

Realignment of roadbed

Stacking first layer

Rolling compaction first layer

Stacking second layer

Rolling compaction second layer

Stacking third layer

Rolling compaction third layer

Stacking fourth layer

Rolling compaction fourth layer

Stacking fifth layer

Rolling compaction fifth layer

Stacking sixth layer

Rolling compaction sixth layer

Driving steel bar

Ballast trimming

0:00

Manual labour

With backhoe

4:003:453:303:153:002:452:302:152:001:451:301:151:000:450:300:15

Figure 28. Construction process



Technology Symposium 2009, Tokyo, Japan, December 2009, pp.

651654 (in Japanese).

Koseki, J. (2012). Use of geosynthetics to improve seismic performance

of earth structures. Geotextiles and Geomembranes, 34, 5168.

Leshchinsky, B. & Ling, H. I. (2013). Numerical modeling of behavior of

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Kyoto University Science Publications, Kyoto, Japan, pp. 244250

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2009, pp. 545548 (in Japanese).

Mohri, Y., Matsushima, K., Yamazaki, S., Lohani, T. N., Tatsuoka, F. &

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S. (2009). Design and specification tests of anti-Derailing guard rail

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Railway Technology Symposium 2009, Tokyo, Japan, December

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reinforced soil retaining walls with full-height rigid facing for the

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Shinkansen, The Japan Railway Engineering Association, Tokyo,

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The Editor welcomes discussion on all papers published in Geosynthetics International. Please email your contribution to

[email protected] by 15 April 2014.



1. INTRODUCTION2. GEOSYNTHETIC BAG METHODFigure 1Figure 2Figure 3

3. HORIZONTAL BEARING CAPACITY TESTS OF BASIC CONFIGURATIONFigure 4Figure 5Figure 6

4. SHAKING TABLE MODEL TESTS ON BASIC CONFIGURATIONS4.1. Test models and procedures4.2. Selection of performance criteriaFigure 7Figure 8Table 1Figure 94.3. Test results

5. HORIZONTAL BEARING CAPACITY TESTS ON IMPROVED CONFIGURATIONS5.1. Test proceduresFigure 10Figure 11Figure 125.2. Test resultsFigure 13Table 2Figure 14

6. SHAKING TABLE MODEL TESTS ON IMPROVED CONFIGURATION6.1. Test model and test procedures6.2. Test resultsFigure 15Figure 16Figure 17

7. PERFORMANCE EVALUATION TESTS FOR THE BAG7.1. Cutting resistance tests for bag materialFigure 18Figure 19Figure 207.2. Cutting resistance tests on selected bag materialsFigure 21Figure 22Table 3Figure 23Table 47.3. Ultraviolet light resistance tests on bag materialFigure 24Figure 25Table 5Table 6

8. FIELD CONSTRUCTION TESTFigure 26Figure 27

9. CONCLUSIONSREFERENCESBrandl 2011Chen et al. 2012Ferellec and McDowell 2012Harada and Kato 2004Ikegami et al. 1982Iwata and Iemura 2003Japan Weathering Test Center 2004JISC (Japan Industrial Standards Committee) 2010aJISC 2010bKachi et al. 2009Kachi et al. 2010Kobayashi et al. 2009Figure 28Koseki 2012Leshchinsky and Ling 2013Matsuda et al. 2009Matsuoka 2003Matsuoka and Liu 2003Matsushima et al. 2008Morimura and Seki 2009Mohri et al. 2009Muramatsu et al. 2009Nagao et al. 2006Osawa and Narusawa 2002RTRI (Railway Technical Research Institute) 1999RTRI 2007Tamura 2006Tanaka and Isoura 1998Tatsuoka et al. 1997Yoshida et al. 2009

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