TechnologyTechnology

Railway Technology Today 1 (Edited by Kanji Wako)

Railway Construction in Japan
Yukinori Koyama
Introduction

Progress of construction
technology

Japan has a relatively small proportionof lowland, consisting mainly of alluvial
coastal plains. Railway construction
started in the early Meiji Era (1868–1912)
and since the construction technology
was still immature, the first lines werebuilt in level coastal areas. The rails werelaid mostly on earth structures such asembankments and cuttings. Many railway bridges over rivers were also built
at that time. Gradually, with progress intunnelling technology, railways wereconstructed connecting towns and cities
previously isolated by mountains.
The post-war period of rapid economic
growth in the 1950s and 1960s saw problems in securing urban land for new railway construction. Moreover, the rapid
spread of automobiles gave rise to severe
city planning problems with more traffic
congestion resulting in railway crossing
accidents. To solve these problems, more
urban railways were built on elevatedsections.
With advances in construction technology, especially shield tunnelling, many
new railways are being constructed underground. In recent years it has becomecompletely impossible to secure newland for railway construction in big cities, although railway demand is still increasing. Furthermore, it is even getting
harder to plan construction of new railways underground because there are already so many buried structures,
including underground railways. Therefore, the future will see a good deal ofeffort in developing new technologies forusing deep underground space, as well
as space above existing railways.

Comparison of Shinkansen lines
by structureFirst, this article looks at changes in Japanese railway technology by comparing
past and current Shinkansen structures(Fig. 1).
The Tokaido Shinkansen—the world’s
first high-speed railway—is built with alarge proportion of earth structures, suchas embankments. This method was chosen to shorten the work term and cut construction costs. It was possible because
maintenance costs were not so high inthose days and no one expected that theshinkansen would operate on the tightschedule of today (about 5 minutes headway).
The Sanyo Shinkansen, completed about
10 years later, runs mostly through mountainous districts. Consequently, morethan 80% of its length is tunnels andbridges (including viaducts).
Rising track maintenance costs due tolabour costs, resulted in more use of concrete slab tracks. However, since con-crete slab track laid on earth structures
requires strict control of track bed deformation, the Tohoku Shinkansen andJoetsu Shinkansen, both completed in
1982, have few such sections.
To minimize railway construction andmaintenance costs, the Nagano-boundshinkansen, which opened on 1 October this year, uses several new techniques
for laying concrete slab track on an earthstructure that is not deformed under thetrain load.

Embankments
Embankments made by heaping andcompacting soil are inexpensive andquick to construct and have long beenused in Japan. A typical embankment has
a quadrilateral cross section (Fig. 2).
Since soil cannot be heaped squarely,
sloping embankments on both sides provide structural stability, meaning that theembankment requires more space thanFigure 1 Changes in Shinkansen Structures

Nagano-boundShinkansen(1997)

39

JoetsuShinkansen(1982)

63

20

Earth structures
Tunnels
Bridges and Viaducts

165

107

TohokuShinkansen(1982)3354

Sanyo
Shinkansen(1975)

115212

TokaidoShinkansen(1964)

174

0100

27281

86200

70291

300

400

500600Length (km)36Japan Railway & Transport Review • December 1997

Copyright © 1997 EJRCF. All rights reserved.

Figure 2 Typical (top) and Geosynthetic-Reinforced Embankments (bottom)

the track actually needs. In addition, soilembankments are easily affected byheavy rain and earthquakes, which are aserious and common problem in Japan.
Consequently, concrete structures wereintroduced in the last 10 years to provide more stability, but still did not solve
the wasted space problem.
Recently, sloped embankments havebeen disappearing to be replaced bygeosynthetic-reinforced embankmentswith vertical concrete retaining walls. In
this method, soil is heaped in layers withhigh-polymer geosynthetic sheets and theentire structure is stabilized by verticalconcrete retaining walls, thus eliminating the wasted space of typical sloped
embankments. Furthermore, no foundation work (pile driving, etc.) is required
even on soft ground and the concrete
walls are not undermined by rain. Consequently, this new method is very economical and has outstanding
stability—these embankments even withstood the Great Hanshin Earthquake that
hit Kobe in January 1995.

Viaducts
Rigid-frame, reinforced concrete (RC),beam and slab viaducts are common in
Japan. They are monolithic structures

Slope(1 : 1.5-1.8)

Gabions
New free space

DrainsConcrete facing wall

Earth
Reinforcing net

with a rigid frame of columns and beams
and a slab serving as the railway track.
This type of viaduct is the most economical and has high resistance to earthquakes.
Many shinkansen were built using rigidframe viaducts to cut construction costs
and work terms. In fact, such viaducts
account for 700 out of the total 2000 kmof shinkansen tracks.
Figure 3 shows the procedure for constructing a rigid-frame viaduct. After thefoundation is completed, the superstructure is built using the scaffold shoring
support method. The columns, beams,

Typical embankment collapsed during Great Hanshin Earthquake

Copyright © 1997 EJRCF. All rights reserved.

Geosynthetics(RTRI)and slab are erected in that order. First,
temporary scaffold shoring is erected.
Then, reinforcing bars and timber formsare set up. Finally, the columns, beams,and slab are poured by the cast-in-placemethod.

Bridges
Concrete railway bridge
Short-span railway bridges (up to 25 m)
are built using RC beams supported onpillars (columns, etc.) at both ends. The
scaffold shoring method described above

Geosynthetic-reinforced embankment with vertical concrete facing wall undamaged by Great Hanshin Earthquake(RTRI)

Japan Railway & Transport Review • December 199737

Technology

Figure 3 Construction of Rigid Frame Viaduct using Scaffold Shoring
Method(a) Constructing foundation(b) Erecting scaffold shoring, reinforcing
bars, and timber forms for lower
columns, and pouring concrete(c) Erecting scaffold shoring, reinforcing
bars, and timber forms for beams,
slab, and upper columns, andpouring concrete

Steel bridges(d) Finished viaduct

Scaffold shoring for rigid frame viaduct

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Japan Railway & Transport Review • December 1997

is used to erect the RC beams. Mediumspan bridges (20 to 50 m), are built usingprestressed concrete (PC) beams insteadof RC. In this case, both scaffold shoring
and crane erection methods are used. In
the crane erection method, prefabricatedgirders are erected on-site using a crane.
Long spans (over 50 m), use rigid-frame
PC bridges with a monolithic structureof columns and beams, or cable-stayed
PC bridges. The cantilever method isusually used to build long-span PC
bridges.
Figure 4 shows the cantilever procedure.
The girders are erected in 3 to 5 m sections. First, movable erection vehicles
are assembled on each side of the central bridge tower. Next, timber forms,
reinforcing bars, and PC tendons andstrands are assembled. Then, the concrete is poured and the PC tendons andstrands are tensioned. The vehicles thenmove outward on both sides to build thenext sections. The procedure is repeated.
This method makes it possible to construct a long-span girder bridge using
relatively simple equipment.

Steel railway bridges can roughly be divided into plate girder bridges (bridgeswith rails above the girders are called
deck plate girder bridges and those withrails under the girders are called through(RTRI)

Completed viaduct(RTRI)

Copyright © 1997 EJRCF. All rights reserved.

Figure 4 Cable-Stayed PC Bridge Construction using Cantilever Method(a) Foundation work forcentral tower

Movable erection vehicle(b) Erecting cantilevers andconstructing tower

Honshu and Shikoku (opened in 1988)
crossing the Seto Inland Sea. The 9.4km section spanning the strait consists ofthree suspension bridges, two cablestayed bridges, and one truss bridge.
These incorporate the latest construction
technology and are among the world’s
longest bridges.

Mountain Tunnels(c) Tensioning PC tendonsand strands and extending
bridge cantilevers(d) Finished bridge

plate girder bridges) and through-truss
bridges with rails under a steel frame.
Normally, these steel railway bridges arefabricated at factories. The steel ismarked, cut, and welded or joined byhigh-strength bolts into a bridge, which

Constructing cable-stayed bridge

Copyright © 1997 EJRCF. All rights reserved.

is then erected on-site.
Recent advances in materials, design, andfabrication technologies have made it
possible to erect huge railway bridges.
A typical example is the chain of combined railway and road bridges between(RTRI)

Japanese railways nationwide passthrough some 3800 mountain tunnels
totalling 2100 km in length, including theSeikan Tunnel (the world’s longest tunnel) completed in 1988. The New Austrian Tunnelling Method (NATM),
composed of the following three stages,
is used most widely today to construct
mountain tunnels.
1. Excavating—blasting with dynamite
or by machine digging with natural
ground above kept intact
2. Supporting—steel supports installedin tunnel, concrete sprayed onto wall,and rock-bolts driven through concrete into tunnel rock
3. Lining—NATM creates tunnel support
by pouring concrete into forms, re-Chain of bridges joining Honshu and Shikoku over Seto Inland Sea—upper deckfor motorway and lower deck for railway(Honshu-Shikoku Bridge Authority)

Japan Railway & Transport Review • December 199739

Technology

Figure 5 Tunnel Construction using Cut-and-CoverMethod(a) Earth-retaining
wall(b) Covering ground (c) Constructing
surface, protectundergrounding utilities,
stationexcavating(d) Back filling,
removing coverplate, restoring
ground surface

Cover plate

Plate girder bridge (RTRI)

Supports

Through truss bridge(RTRI)

used for relatively shallow tunnels andwhere there are no existing structures onor under the ground. However, the shield
method, which permits deep tunnels tobe dug horizontally, is widely used today.

placing the conventional steel andpile supports. This has become thestandard method since it was firstused for the Nakayama Tunnel on theJoetsu Shinkansen (completed in1982).
Recently, the tunnel excavation has become increasingly automated and sometunnels have been constructed using
shield tunnelling machines.

Cut-and-cover method
Complex underground stations arechiefly constructed using the cut-andcover method (Fig. 5).
First, an earth-retaining structure of steelpiles, concrete, etc., is constructed fromground level, then the open cut is covered so as not to interfere with the above
ground traffic. Next, the ground is excavated to the required depth using suitable supports and taking care not todamage underground utilities, such as

Subways
For some time after the construction of
the first tunnel, subways were built using exclusively the cut-and-covermethod. In this method, the ground iscut to the tunnel depth, so it can only bewater supply, sewage, and gas pipes.
After the station is built, the above space
is back-filled to restore the ground surface.

Shield method
In the shield method, a shield (steel shell)
with a cutter at the front is used to tunnel
through the ground. The excavatedground is prevented from collapsing by
the pressure of slurry, etc., pumped backto the work face. Segment concrete
blocks prefabricated elsewhere are assembled automatically inside the shieldbehind the work face to finish the tunnel(Fig. 6). Shield tunelling permits fast, relatively safe construction work, and neither interferes with traffic above groundnor adversely affects nearby undergroundFigure 6 Tunnel Construction using Shield Tunneling
Machine (Pressurized Slurry Shield Type)
Slurry treatment plantPShield

Backfill grouting

Segments
Slurry feed pipePP

Slurry discharge pipe

PJackCutter disk

P Pump

Erecting prefabricated segments behind shield in Tokyo’s new Subway Line No. 7of Teito Rapid Transit Authority(M. Shimizu)

40

Japan Railway & Transport Review • December 1997

Copyright © 1997 EJRCF. All rights reserved.

Figure 7 Longitudinal Cross Section of Seikan Tunnel
Tunnel length (53.8km)
Underground section(13.55km)(m)400Tunnel portal
at Hamana,
Imabetsu-cho,
Honshuside
Shaft tosurface

300
200
100

Smoke extraction
machine room

Smoke extraction
machine room
Ventilator
Ventilator
machine room
machine room
Tsugaru Strait

0Main

-100
-200
-300

140m

tunne

ServicInspection
point

Pilot tunnel

e tunnlel

100meServic0510Mainltunne

ltunneInspection point

Pilot tunnel Water

drainagearea

Water drainage area

1520253035404550 (km)Figure 8 Seikan Tunnel between Honshu and Hokkaido
showing main, service and pilot tunnels

Main tunnel

30.00mServicetunnel

Shotcrete thickness 0.12m~0.15m

0m

0~0.7 90m
0.

4.8s of 600m)
necting gallery (at interval

3.47~4.10m

With a length of 53.8 km, the Seikan Tunnel connecting Honshu and Hokkaido
is the world’s longest tunnel (Fig. 7).
Construction started in 1971 and wascompleted in 1988. Because of the exceptional length, pilot and service tunnels were also dug. The pilot tunnel wasused mainly for geological surveys, andthe service tunnel alongside the maintunnel was used as a passage for construction workers and for removal of excavated rock.
The main tunnel diameter is 9.6 m to allow passage of shinkansen in the future.
The submarine section is 23.3-km longand the deepest point is 240 m beneathsea level. Construction proceeded withgreat difficulty because of the presenceof huge volumes of water and high earthpressures. These difficulties were overcome by developing several new technologies, including grouting by injecting
a high-pressure sodium silicate-cement
mixture to stop the water, shotcreting by
spraying concrete immediately after excavation to stabilize the bedrock, andlong-distance horizontal boring.
■

Underground section(17.0km)Tunnel Portal
at Yunosato,
Shirenai-cho,
Hokkaido
side
Shaft tosurface

Con

1.00m

0.50m

Seikan Tunnel

Underwater section(23.3km)118.00~0.00

structures.
In recent years, since shallow underground space in big cities is almost fully
used, more subway stations are being
constructed deeper underground, using
the shield method.

4.00~
5.00m

11.00~ 11.40m

15.00m15.00mShotcrete thickness
0.12m~0.15m
3.07~
4.22m

Pilottunnel
3.60~
5.00m

Yukinori KoyamaKanji Wako

Mr Yukinori Koyama is General Manager of the Structure Tech-

Mr Kanji Wako is Director in Charge of Research and Develop-

nology Development Division at the Railway Technical Researchment at RTRI. He joined JNR in 1961 after graduating in engi-

Institute (RTRI). He joined JNR in 1971 after graduating fromneering from Tohoku University. He is the supervising editor for

the University of Tokyo in Engineering, and transferred to RTRI

this new series on Railway Technology Today.

in 1987.

Copyright © 1997 EJRCF. All rights reserved.

Japan Railway & Transport Review • December 199741