Railway Construction in Japan Yukinori Koyama

Technolo Technology Railway Technology Today 1 (Edited by Kanji Wako) Railway Construction in Japan Yukinori Koyama Comparison of Shinkansen lines crete slab track laid on earth structures Introduction by structure requires strict control of track bed defor- First, this article looks at changes in Japa- mation, the Tohoku Shinkansen and Progress of construction nese railway technology by comparing Joetsu Shinkansen, both completed in technology past and current Shinkansen structures 1982, have few such sections. Japan has a relatively small proportion (Fig. 1). To minimize railway construction and of lowland, consisting mainly of alluvial The Tokaido Shinkansen—the world’s maintenance costs, the Nagano-bound coastal plains. Railway construction first high-speed railway—is built with a shinkansen, which opened on 1 Octo- started in the early Meiji Era (1868–1912) large proportion of earth structures, such ber this year, uses several new techniques and since the construction technology as embankments. This method was cho- for laying concrete slab track on an earth was still immature, the first lines were sen to shorten the work term and cut con- structure that is not deformed under the built in level coastal areas. The rails were struction costs. It was possible because train load. laid mostly on earth structures such as maintenance costs were not so high in embankments and cuttings. Many rail- those days and no one expected that the way bridges over rivers were also built shinkansen would operate on the tight Embankments at that time. Gradually, with progress in schedule of today (about 5 minutes head- tunnelling technology, railways were way). Embankments made by heaping and constructed connecting towns and cities The Sanyo Shinkansen, completed about compacting soil are inexpensive and previously isolated by mountains. 10 years later, runs mostly through moun- quick to construct and have long been The post-war period of rapid economic tainous districts. Consequently, more used in Japan. A typical embankment has gy growth in the 1950s and 1960s saw prob- than 80% of its length is tunnels and a quadrilateral cross section (Fig. 2). lems in securing urban land for new rail- bridges (including viaducts). Since soil cannot be heaped squarely, way construction. Moreover, the rapid Rising track maintenance costs due to sloping embankments on both sides pro- spread of automobiles gave rise to severe labour costs, resulted in more use of con- vide structural stability, meaning that the city planning problems with more traffic crete slab tracks. However, since con- embankment requires more space than congestion resulting in railway crossing accidents. To solve these problems, more urban railways were built on elevated Figure 1 Changes in Shinkansen Structures sections. With advances in construction technology, especially shield tunnelling, many Nagano-bound new railways are being constructed un- Shinkansen 39 63 20 Earth structures (1997) derground. In recent years it has become Tunnels completely impossible to secure new Bridges and Viaducts Joetsu land for railway construction in big cit- Shinkansen 165 107 3 ies, although railway demand is still in- (1982) creasing. Furthermore, it is even getting Tohoku harder to plan construction of new rail- Shinkansen 354 115 27 ways underground because there are al- (1982) ready so many buried structures, including underground railways. There- Sanyo Shinkansen 212 281 70 fore, the future will see a good deal of (1975) effort in developing new technologies for using deep underground space, as well Tokaido Shinkansen 174 86 291 as space above existing railways. (1964) 0 100 200 300 400 500 600 Length (km) 36 Japan 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, soil embankments are easily affected by Slope heavy rain and earthquakes, which are a (1 : 1.5-1.8) serious and common problem in Japan. Consequently, concrete structures were introduced in the last 10 years to pro- vide more stability, but still did not solve the wasted space problem. Recently, sloped embankments have been disappearing to be replaced by Gabions geosynthetic-reinforced embankments New free space Geosynthetics with vertical concrete retaining walls. In this method, soil is heaped in layers with Concrete facing wall high-polymer geosynthetic sheets and the Drains Earth entire structure is stabilized by vertical Reinforcing net concrete retaining walls, thus eliminat- ing the wasted space of typical sloped embankments. Furthermore, no foundation work (pile driving, etc.) is required with a rigid frame of columns and beams and slab are erected in that order. First, even on soft ground and the concrete and a slab serving as the railway track. temporary scaffold shoring is erected. walls are not undermined by rain. Con- This type of viaduct is the most economi- Then, reinforcing bars and timber forms sequently, this new method is very eco- cal and has high resistance to earth- are set up. Finally, the columns, beams, nomical and has outstanding quakes. and slab are poured by the cast-in-place stability—these embankments even with- Many shinkansen were built using rigid- method. stood the Great Hanshin Earthquake that frame viaducts to cut construction costs hit Kobe in January 1995. and work terms. In fact, such viaducts account for 700 out of the total 2000 km Bridges of shinkansen tracks. Viaducts Figure 3 shows the procedure for con- Concrete railway bridge structing a rigid-frame viaduct. After the Short-span railway bridges (up to 25 m) Rigid-frame, reinforced concrete (RC), foundation is completed, the superstruc- are built using RC beams supported on beam and slab viaducts are common in ture is built using the scaffold shoring pillars (columns, etc.) at both ends. The Japan. They are monolithic structures support method. The columns, beams, scaffold shoring method described above Typical embankment collapsed during Great Hanshin Earthquake (RTRI) Geosynthetic-reinforced embankment with vertical concrete facing wall undam- aged by Great Hanshin Earthquake (RTRI) Copyright © 1997 EJRCF. All rights reserved. Japan Railway & Transport Review • December 1997 37 Technology is used to erect the RC beams. Medium- span bridges (20 to 50 m), are built using Figure 3 Construction of Rigid Frame Viaduct using Scaffold Shoring Method prestressed concrete (PC) beams instead of RC. In this case, both scaffold shoring (a) Constructing foundation and crane erection methods are used. In the crane erection method, prefabricated girders are erected on-site using a crane. Long spans (over 50 m), use rigid-frame PC bridges with a monolithic structure of columns and beams, or cable-stayed PC bridges. The cantilever method is usually used to build long-span PC (b) Erecting scaffold shoring, reinforcing bridges. bars, and timber forms for lower Figure 4 shows the cantilever procedure. columns, and pouring concrete 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 and strands are assembled. Then, the concrete is poured and the PC tendons and (c) Erecting scaffold shoring, reinforcing bars, and timber forms for beams, strands are tensioned. The vehicles then slab, and upper columns, and move outward on both sides to build the pouring concrete next sections. The procedure is repeated. This method makes it possible to construct a long-span girder bridge using relatively simple equipment. Steel bridges (d) Finished viaduct Steel railway bridges can roughly be di- vided into plate girder bridges (bridges with rails above the girders are called deck plate girder bridges and those with rails under the girders are called through Scaffold shoring for rigid frame viaduct (RTRI) Completed viaduct (RTRI) 38 Japan Railway & Transport Review • December 1997 Copyright © 1997 EJRCF. All rights reserved. Figure 4 Cable-Stayed PC Bridge Construction using Cantilever Method (a) Foundation work for Honshu and Shikoku (opened in 1988) central tower crossing the Seto Inland Sea. The 9.4- km section spanning the strait consists of three suspension bridges, two cable- Movable erection vehicle stayed bridges, and one truss bridge. These incorporate the latest construction (b) Erecting cantilevers and technology and are among the world’s constructing tower longest bridges. Mountain Tunnels Japanese railways nationwide pass (c) Tensioning PC tendons through some 3800 mountain tunnels and strands and extending bridge cantilevers totalling 2100 km in length, including the Seikan Tunnel (the world’s longest tunnel) completed in 1988. The New Aus- trian Tunnelling Method (NATM), composed of the following three stages, is used most widely today to construct (d) Finished bridge mountain tunnels. 1. Excavating—blasting with dynamite or by machine digging with natural ground above kept intact 2. Supporting—steel supports installed plate girder bridges) and through-truss is then erected on-site. in tunnel, concrete sprayed onto wall, bridges with rails under a steel frame. Recent advances in materials, design, and and rock-bolts driven through con- Normally, these steel railway bridges are fabrication technologies have made it crete into tunnel rock fabricated at factories. The steel is possible to erect huge railway bridges. 3. Lining—NATM creates tunnel support marked, cut,

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