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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: takashi.kachi@cn-const.co.jp2General 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: kobm@jr-central.co.jp3Executive 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: m.seki@jr-central.co.jp4Professor, 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: koseki@iis.u-tokyo.ac.jp
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
Geosynthetics International, 2013, 20, No. 5
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
Geosynthetics International, 2013, 20, No. 5
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
0
2
4
6
8
10
12
14
16
18
0Hor
izon
tal d
ispl
acem
ent a
t the
top
ofst
acke
d ba
gs (
mm
)
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)
Reinforcement of railway ballasted track with geosynthetic bags for preventing derailment 319
Geosynthetics International, 2013, 20, No. 5
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
200
400
600
800
1000
1200
1400
0.1
Four
ier
spec
trum
(ga
l s
ec)
Frequency (Hz)
500
0
500
1000
1500
20000 5 10 15 20 25 30 35
Time (s)
Acc
eler
atio
n (g
al)
max 928.6min 778.7
500
0
500
1000
1500
20000 5 10 15 20 25 30 35
Time (s)
Acc
eler
atio
n (g
al)
max 1338.3min 1027.6
500
0
500
1000
1500
20000 5 10 15 20 25 30 35
Time (s)
Acc
eler
atio
n (g
al)
101
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
320 Kachi, Kobayashi, Seki and Koseki
Geosynthetics International, 2013, 20, No. 5
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
0
500
1000
1500
0 5 10 15 20 25 30 35Time (s)
Inpu
tA
ccel
era
tion
(gal
)
25201510
05
10
Hor
izon
tal
disp
lace
men
t(m
m)
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)
Reinforcement of railway ballasted track with geosynthetic bags for preventing derailment 321
Geosynthetics International, 2013, 20, No. 5
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 10.6 mm
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)
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 20.3 mm
Bottom of the bags -- Top of the bags -- Tie
5040302010
80080
100
100
200
1220
Cross-section: units are mm
0
Tie
Bottom
Top
Maximum horizontal displacement (mm)
1000
1500
Figure 12. Results of reinforced bag test (case 3)
322 Kachi, Kobayashi, Seki and Koseki
Geosynthetics International, 2013, 20, No. 5
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
22.5
400
200
80
400
40080
300
400
400
50
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
Reinforcement of railway ballasted track with geosynthetic bags for preventing derailment 323
Geosynthetics International, 2013, 20, No. 5
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
5.0
10.0
15.0
20.0
25.0
30.0
35.0
0
Hor
izon
tal d
ispl
acem
ent a
t the
top
ofst
acke
d ba
gs (
mm
)
Horizonal bearing capacity (kN)
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
324 Kachi, Kobayashi, Seki and Koseki
Geosynthetics International, 2013, 20, No. 5
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
Bottom of the block -- of the blockTop -- Tie
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 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)
Reinforcement of railway ballasted track with geosynthetic bags for preventing derailment 325
Geosynthetics International, 2013, 20, No. 5
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
Bottom of the block -- of the blockTop -- Tie
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
326 Kachi, Kobayashi, Seki and Koseki
Geosynthetics International, 2013, 20, No. 5
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
Reinforcement of railway ballasted track with geosynthetic bags for preventing derailment 327
Geosynthetics International, 2013, 20, No. 5
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
328 Kachi, Kobayashi, Seki and Koseki
Geosynthetics International, 2013, 20, No. 5
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
Reinforcement of railway ballasted track with geosynthetic bags for preventing derailment 329
Geosynthetics International, 2013, 20, No. 5
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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Excavating ballasts
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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
330 Kachi, Kobayashi, Seki and Koseki
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discussion@geosynthetics-international.com by 15 April 2014.
Reinforcement of railway ballasted track with geosynthetic bags for preventing derailment 331
Geosynthetics International, 2013, 20, No. 5
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