Railway Technology Today 1 (Edited by Kanji Wako) Railway … · Cut-and-cover method Complex...

36 Japan Railway & Transport Review • December 1997

Technology

Technolo gy

Copyright © 1997 EJRCF. All rights reserved.

Railway Technology Today 1 (Edited by Kanji Wako)

Railway Construction in JapanYukinori Koyama

Introduction

Progress of constructiontechnologyJapan has a relatively small proportionof lowland, consisting mainly of alluvialcoastal plains. Railway constructionstarted in the early Meiji Era (1868–1912)and since the construction technologywas still immature, the first lines werebuilt in level coastal areas. The rails werelaid mostly on earth structures such asembankments and cuttings. Many rail-way bridges over rivers were also builtat that time. Gradually, with progress intunnelling technology, railways wereconstructed connecting towns and citiespreviously isolated by mountains.The post-war period of rapid economicgrowth in the 1950s and 1960s saw prob-lems in securing urban land for new rail-way construction. Moreover, the rapidspread of automobiles gave rise to severecity planning problems with more trafficcongestion resulting in railway crossingaccidents. To solve these problems, moreurban railways were built on elevatedsections.With advances in construction technol-ogy, especially shield tunnelling, manynew railways are being constructed un-derground. In recent years it has becomecompletely impossible to secure newland for railway construction in big cit-ies, although railway demand is still in-creasing. Furthermore, it is even gettingharder to plan construction of new rail-ways underground because there are al-ready so many buried structures,including underground railways. There-fore, the future will see a good deal ofeffort in developing new technologies forusing deep underground space, as wellas space above existing railways.

Comparison of Shinkansen linesby structureFirst, this article looks at changes in Japa-nese railway technology by comparingpast and current Shinkansen structures(Fig. 1).The Tokaido Shinkansen—the world’sfirst high-speed railway—is built with alarge proportion of earth structures, suchas embankments. This method was cho-sen to shorten the work term and cut con-struction costs. It was possible becausemaintenance costs were not so high inthose days and no one expected that theshinkansen would operate on the tightschedule of today (about 5 minutes head-way).The Sanyo Shinkansen, completed about10 years later, runs mostly through moun-tainous districts. Consequently, morethan 80% of its length is tunnels andbridges (including viaducts).Rising track maintenance costs due tolabour costs, resulted in more use of con-crete slab tracks. However, since con-

crete slab track laid on earth structuresrequires strict control of track bed defor-mation, the Tohoku Shinkansen andJoetsu Shinkansen, both completed in1982, have few such sections.To minimize railway construction andmaintenance costs, the Nagano-boundshinkansen, which opened on 1 Octo-ber this year, uses several new techniquesfor 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 hasa quadrilateral cross section (Fig. 2).Since soil cannot be heaped squarely,sloping embankments on both sides pro-vide structural stability, meaning that theembankment requires more space than

Figure 1 Changes in Shinkansen Structures

0 100 200 300 400 500 600

TokaidoShinkansen

(1964)

SanyoShinkansen

(1975)

TohokuShinkansen

(1982)

JoetsuShinkansen

(1982)

Nagano-boundShinkansen

(1997)

Length (km)

Earth structuresTunnelsBridges and Viaducts

165

354

212

174 29186

281 70

115 27

107 3

206339

37Japan Railway & Transport Review • December 1997Copyright © 1997 EJRCF. All rights reserved.

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 pro-vide more stability, but still did not solvethe wasted space problem.Recently, sloped embankments havebeen disappearing to be replaced bygeosynthetic-reinforced embankmentswith vertical concrete retaining walls. Inthis method, soil is heaped in layers withhigh-polymer geosynthetic sheets and theentire structure is stabilized by verticalconcrete retaining walls, thus eliminat-ing the wasted space of typical slopedembankments. Furthermore, no founda-tion work (pile driving, etc.) is requiredeven on soft ground and the concretewalls are not undermined by rain. Con-sequently, this new method is very eco-n o m i c a l a n d h a s o u t s t a n d i n gstability—these embankments even with-stood the Great Hanshin Earthquake thathit Kobe in January 1995.

Viaducts

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

with a rigid frame of columns and beamsand a slab serving as the railway track.This type of viaduct is the most economi-cal and has high resistance to earth-quakes.Many shinkansen were built using rigid-frame viaducts to cut construction costsand work terms. In fact, such viaductsaccount for 700 out of the total 2000 kmof shinkansen tracks.Figure 3 shows the procedure for con-structing a rigid-frame viaduct. After thefoundation is completed, the superstruc-ture is built using the scaffold shoringsupport method. The columns, beams,

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 bridgeShort-span railway bridges (up to 25 m)are built using RC beams supported onpillars (columns, etc.) at both ends. Thescaffold shoring method described above

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

Typical embankment collapsed during Great Hanshin Earthquake (RTRI) Geosynthetic-reinforced embankment with vertical concrete facing wall undam-aged by Great Hanshin Earthquake (RTRI)

New free space

Gabions

Drains

Reinforcing net

Earth

Geosynthetics

Concrete facing wall

Slope(1 : 1.5-1.8)


Technology


is used to erect the RC beams. Medium-span bridges (20 to 50 m), are built usingprestressed concrete (PC) beams insteadof RC. In this case, both scaffold shoringand crane erection methods are used. Inthe crane erection method, prefabricatedgirders are erected on-site using a crane.Long spans (over 50 m), use rigid-framePC bridges with a monolithic structureof columns and beams, or cable-stayedPC bridges. The cantilever method isusually used to build long-span PCbridges.Figure 4 shows the cantilever procedure.The girders are erected in 3 to 5 m sec-tions. First, movable erection vehiclesare assembled on each side of the cen-tral bridge tower. Next, timber forms,reinforcing bars, and PC tendons andstrands are assembled. Then, the con-crete 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 con-struct a long-span girder bridge usingrelatively simple equipment.

Steel bridgesSteel railway bridges can roughly be di-vided into plate girder bridges (bridgeswith rails above the girders are calleddeck plate girder bridges and those withrails under the girders are called through

Figure 3 Construction of Rigid Frame Viaduct using Scaffold ShoringMethod

Scaffold shoring for rigid frame viaduct (RTRI) Completed viaduct (RTRI)

(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, and pouring concrete

(d) Finished viaduct


plate girder bridges) and through-trussbridges 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

Figure 4 Cable-Stayed PC Bridge Construction using Cantilever Method

Constructing cable-stayed bridge (RTRI)

is then erected on-site.Recent advances in materials, design, andfabrication technologies have made itpossible to erect huge railway bridges.A typical example is the chain of com-bined railway and road bridges between

Honshu and Shikoku (opened in 1988)crossing the Seto Inland Sea. The 9.4-km section spanning the strait consists ofthree suspension bridges, two cable-stayed bridges, and one truss bridge.These incorporate the latest constructiontechnology and are among the world’slongest bridges.

Mountain Tunnels

Japanese railways nationwide passthrough some 3800 mountain tunnelstotalling 2100 km in length, including theSeikan Tunnel (the world’s longest tun-nel) completed in 1988. The New Aus-trian Tunnelling Method (NATM),composed of the following three stages,is used most widely today to constructmountain tunnels.1. Excavating—blasting with dynamite

or by machine digging with naturalground above kept intact

2. Supporting—steel supports installedin tunnel, concrete sprayed onto wall,and rock-bolts driven through con-crete into tunnel rock

3. Lining—NATM creates tunnel supportby 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)

(a) Foundation work for central tower

(b) Erecting cantilevers and constructing tower

(c) Tensioning PC tendons and strands and extending bridge cantilevers

(d) Finished bridge

Movable erection vehicle


Technology


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 be-come increasingly automated and sometunnels have been constructed usingshield tunnelling machines.

Subways

For some time after the construction ofthe first tunnel, subways were built us-ing exclusively the cut-and-covermethod. In this method, the ground iscut to the tunnel depth, so it can only be

used for relatively shallow tunnels andwhere there are no existing structures onor under the ground. However, the shieldmethod, which permits deep tunnels tobe dug horizontally, is widely used to-day.

Cut-and-cover methodComplex underground stations arechiefly constructed using the cut-and-cover method (Fig. 5).First, an earth-retaining structure of steelpiles, concrete, etc., is constructed fromground level, then the open cut is cov-ered so as not to interfere with the aboveground traffic. Next, the ground is exca-vated to the required depth using suit-able supports and taking care not todamage underground utilities, such as

Plate girder bridge (RTRI)

Through truss bridge (RTRI)

water supply, sewage, and gas pipes.After the station is built, the above spaceis back-filled to restore the ground sur-face.

Shield methodIn the shield method, a shield (steel shell)with a cutter at the front is used to tunnelthrough the ground. The excavatedground is prevented from collapsing bythe pressure of slurry, etc., pumped backto the work face. Segment concreteblocks prefabricated elsewhere are as-sembled automatically inside the shieldbehind the work face to finish the tunnel(Fig. 6). Shield tunelling permits fast, rela-tively safe construction work, and nei-ther interferes with traffic above groundnor adversely affects nearby underground

Figure 5 Tunnel Construction using Cut-and-CoverMethod

Cover plate

Supports

(a) Earth-retainingwall

(b) Covering groundsurface, protect-ing utilities,excavating

(c) Constructingundergroundstation

(d) Back filling,removing coverplate, restoringground surface

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

Figure 6 Tunnel Construction using Shield TunnelingMachine (Pressurized Slurry Shield Type)

P P P

P

Slurry treatment plant

Slurry feed pipe

P Pump

Slurry discharge pipe

Shield Backfill grouting Segments

JackCutter disk


Yukinori Koyama

Mr Yukinori Koyama is General Manager of the Structure Tech-

nology Development Division at the Railway Technical Research

Institute (RTRI). He joined JNR in 1971 after graduating from

the University of Tokyo in Engineering, and transferred to RTRI

in 1987.

Kanji Wako

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

ment at RTRI. He joined JNR in 1961 after graduating in engi-

neering from Tohoku University. He is the supervising editor for

this new series on Railway Technology Today.

structures.In recent years, since shallow under-ground space in big cities is almost fullyused, more subway stations are beingconstructed deeper underground, usingthe shield method.

Seikan Tunnel

With a length of 53.8 km, the Seikan Tun-nel connecting Honshu and Hokkaidois the world’s longest tunnel (Fig. 7).Construction started in 1971 and wascompleted in 1988. Because of the ex-ceptional length, pilot and service tun-nels were also dug. The pilot tunnel wasused mainly for geological surveys, andthe service tunnel alongside the maintunnel was used as a passage for con-struction workers and for removal of ex-cavated rock.The main tunnel diameter is 9.6 m to al-low 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 over-come by developing several new tech-nologies, including grouting by injectinga high-pressure sodium silicate-cementmixture to stop the water, shotcreting byspraying concrete immediately after ex-cavation to stabilize the bedrock, andlong-distance horizontal boring. �

Figure 8 Seikan Tunnel between Honshu and Hokkaidoshowing main, service and pilot tunnels

0.70~

0.90m

4.80m

0.50

m

11.00~ 11.40m15.00m15.00m

1.00m

30.00m

Shotcrete thickness 0.12m~0.15m

118.

00~

0.00

4.00~5.00m

3.47

~4.

10m

Shotcrete thickness0.12m~0.15m

3.07~4.22m

3.60~5.00m

Connecting gallery (at intervals of 600m)

Servicetunnel

Main tunnel

Pilottunnel

Smoke extractionmachine room

Tunnel portalat Hamana,Imabetsu-cho,Honshuside Ventilator

machine room

Smoke extractionmachine room

Tunnel Portalat Yunosato,

Shirenai-cho,Hokkaido

side

Ventilatormachine room

Underground section(13.55km)

Underwater section(23.3km)

Tunnel length (53.8km)

Underground section(17.0km)

Shaft tosurface

Tsugaru Strait

Inspection pointInspectionpoint

Water drainage areaWaterdrainagearea

Pilot tunnel

Service tunnel

Pilot tunnel

Service tunnelMain tunnel Main tunnel

Shaft tosurface

140m

100m

5 10 15 20 25 30 35 40 45 50 (km)0

400(m)

300

200

100

0

-100

-200

-300

Figure 7 Longitudinal Cross Section of Seikan Tunnel

Railway Technology Today 1 (Edited by Kanji Wako) Railway … · Cut-and-cover method Complex...

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