The World's Longest Terrestrial Railway Tunnel
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PROJECT REPORT The World’s Longest Terrestrial Railway Tunnel Iwate-Ichinohe Tunnel on the Tohoku New Trunk Line Hitoshi YAMAJI Member of JSCE, Civil Engineering Team Leader, Deputy General Manager of Civil Engineering Designing Department, Sumitomo Construction Co., Ltd. (former member of Editorial Committee on Journal of JSCE) Photo 1. Blasting and excavating in the Torigoe construction section; efficient working in a complex geology Foreword clear view of the mountain. The Kitami river Welcome by Mt. Iwate was already high from the melting snow. Riding the "Yamabiko" train on the Tohoku Though the weather was still chilly, people Shinkansen (Bullet Train) line to Morioka, my were looking forward to their chance to enjoy aim is to collect material for this article on the the cherry and Japanese apricot trees in full Iwate-Ichinohe Tunnel, which will be the world’s bloom during the Golden Week holidays that longest terrestrial railway tunnel upon comple- begin in later April. Coming from further south, tion. Leaving Tokyo in mid-April, where the I was surprised that both trees bloom together, cherry trees had just shed their blossoms, the as it is commonly held that the apricot tree train proceeded north through scenery that comes out first. But enough of these diver- gradually regressed back to early spring before sions; I will now describe the tunnel itself. the cherries come into bloom. As the train approached Morioka Station, the old woman The Morioka-Aomori section of the Tohoku sitting next to me pointed out the snow-capped Shinkansen magnificence of Mt. Iwate out to the west. She reminded me how lucky it was to get such a The Tohoku Shinkansen is a high-speed passenger 18 Midou sec- Surinuka sec- Higyo sec- Kotsunagi sec- Mega sec- Ichinohe sec- Torikoshi sec- tion 3,840m tion 4,110m tion 3,540m tion 3,610m tion 3,720m tion 3,990m tion 3,000m Ramp: 1,268m Ramp: 1,051m Ramp: 552m Ramp: 524m Inclined shaft: 411m Aomori Aomori To Tokyo Iwate-Ichinohe Tunnel L = 25.810 km Portal at Iwate end To Aomori Portal at Ichinohe end Iwate Akita Fig. 3 Longitudinal section of tunnel showing Morioka construction sections Fig. 1 Location of Iwate-Ichinohe Tunnel between Steel support Morioka and Aomori on the Tohoku Shinkansen Rock bolt Spray concrete Welded wire mesh Lining con- Year Total crete Name opened Country Use length (km) Oshimizu 1982 Japan Railway 22.2 Approx. 7.7m Simplon II 1922 Italy and Railway 20.2 Switzerland Invert concrete Concrete subgrade Apenin 1934 Italy Railway 18.5 Approx. 9.5m Center drain pipe Gotthard 1980 Switzerland Railway 16.3 Rokko 1972 Japan Road 16.3 Fig. 4 Typical tunnel Fig. 5 Standard NATM support New Furuka 1982 Switzerland Railway 15.4 section arrangement Haruna 1982 Japan Railway 15.4 Gotthard 1982 Switzerland Railway 15.0 Nakayama 1982 Japan Railway 14.9 Iwate-Ichinohe Tunnel Retzberg 1913 Switzerland Railway 14.6 Fig. 2 List of the ten longest terrestrial tunnels; undersea The Iwate-Ichinohe Tunnel is located near the mid- tunnels such as the Seikan Tunnel are not point of the section in northern Iwate Prefecture (Figure included. 1). The 25.81 km long tunnel will be the world's longest railroad with a total length of approximately 675 km and terrestrial railway tunnel upon completion (Figure 2). authorized under the National Shinkansen Development Following survey work that began in 1988, full-scale Law. Ultimately, it will link Tokyo with Aomori in the construction commenced in 1991. To reduce construc- north, via the cities of Omiya, Utsunomiya, Sendai, and tion costs and tunneling time, the tunnel has been divid- Morioka. ed into seven sections. In order from the portal at the Tunnels form much of the section between Morioka Tokyo end, these are known as: Midou, Surinuka, in Iwate Prefecture and Hachinohe in Aomori Higyo, Kotsunagi, Mega, Ichinohe, and Torigoe. Ramps Prefecture. The total distance between these two sta- or inclined shafts were built to provide access to the tions is 96.6 km, of which 94.5 km is currently under intermediate five sections (Figure 3). Such access is construction. Of this, tunnels account for 69.4 km, or essential in the construction of such a long tunnel. The 73% of the total, with open sections such as bridges, standard cross-sectional dimensions of the tunnel are viaducts, and other earthworks totaling 25.1 km or 27%. approximately 7.7 m and 9.5 m in internal height and The basic technical specifications for the railroad in this width, respectively (Figure 4). The tunnel has an uphill section are: a maximum train speed of 260 km/h, a mini- gradient of 0.5% from the portal on the Tokyo side up to mum curve radius of 4,000 m, a steepest gradient of 2%, a high point between the Midou and Surinuka sections. a track center-to-center distance of 4.3 m, and a power There is then a downhill gradient of 1% down to the por- supply of 25 kV AC. Rapid progress is being made with tal at the Aomori end. construction, and the section is scheduled for opening in December 2002 in time for the 2003 Winter Asian Topography and geology Games. Topographically, the tunnel passes through hilly ter- 19 Full-face tunneling Bench-cut method Fig. 6 NATM tunneling systems Photo 2. Movable form placed at the Tokyo portal of the rain bounded by the Kitakami Mountains to the east and Midou section the Ou Mountains, including Mt. Nanashigure and Mt. Building slab track Nishidake, to the east. Near the portal at the Tokyo end, Rail Rail welding Loading, delivering, (primary delivery and laying 200m long the Higyo construction section (in Ichinohe Town in welding) sections Embedding Temporary track Transporting Injection of Rail Rail welding Adjust- anchors laying (gauge: and laying track CA mortar placement (secondary ment of Nakayama District) marks the watershed that divides the 1.435m) slabs welding) track Mabuchi river, flowing north, from the Kitakami river Fabrication of Transportation Unloading track slabs that flows south. Procedure for laying slab track (on rails with mobile works vehicle) The geology around the tunnel site is classified 1. Rail laying (single track) 2. Slab delivery and laying Self-propelled vehicle (rail roughly into three types. A section measuring about 17 laying vehicle) km from the southern portal is characterized by argillite, Rail feed unit Slab delivery and laying vehicle granodiorite, hornfels, and chert in Mesozoic and Mortar injection vehicle 3. Injection of mortar (tandem injection vehicle) 4. Rail laying Paleozoic strata. An intermediate section of approxi- mately 5 km long is ground vulnerable to swelling con- sisting of crushed volcanic tuff of the Yotsueki stratum Fig. 7 Procedure for laying track for the Morioka- of the Neogene period. This potentially swelling ground Hachinohe section of the Tohoku Shinkansen is the chief source of difficulties with the tunneling work, and the measures used to counter the difficulties explosives inserted in the holes. Mechanical excavation are described later. The final section at the Aomori end, makes use of tunneling machines such as free-cross-sec- measuring about 4 km in length, is dominated by tion excavating machines. Further, there is a choice argillite in the Mesozoic and Paleozoic strata, and vol- between full-face tunneling and the bench-cut method; canic tuff in the Yotsueki stratum as well as mudstone the former is suitable for good ground, while the latter is and andesite of the Monnosawa stratum of the Neogene the standard form of NATM and it achieves tunnel clos- period. The geology of the site is complex and many ing at a relatively early stage. The choice of these meth- faults cross the tunnel path. ods, also, depends on the ground conditions (Figure 6). After mucking out, primary shotcrete is first cast, steel Tunneling method supports are erected, the secondary shotcrete placed, rock bolts installed, and finally primary lining is com- Many tunneling methods are in common use, and a pleted. After that, the lining concrete is cast using a suitable one is generally chosen according to geology, movable form (called centering). tunnel dimensions, and other factors. The New Austrian Tunneling Method (NATM) was adopted in this case. First day of site tour As shown in Figure 5, this method makes the most of the ground's bearing capacity through the use of a combina- After alighting from the Shinkansen, I visited the tion of rock bolts, shotcrete, and steel supports. The Morioka Branch of Japan Railway Construction Public choice between blasting-excavating or mechanical exca- Corp., where I was briefed on the project. From there, I vation depends on ground conditions. Blasting-excavat- headed north up National Highway No. 4 toward the ing entails drilling holes in the rock and detonating construction site. A milestone along the way indicates a 20 Slab track Ballast track Ballast Prestressed concrete tie 60 rail 60 rail Clamp CA mortar Concrete Tack slab projection Clamp Subgrade: reinforced concrete Fig. 8 Slab track and ballasted track Photo 3. Laying track slabs; teamwork is the key R = 5.2 m, allowance for deformation: 0.15 m on one side Spray concrete on upper half of tunnel: t = 25 cm (Vinylon fiber content: 0.75% by vol.; silica fume distance of 570 km from Tokyo; given that the distance content: 5%) Rock bolt: D25, L = 4 m x 44 sets/m by Shinkansen is 540 km, there is no great difference Steel arch support between road and rail. However, the train took only H-200x200 mm, center-to-center: 1.0 m about 2 and a half hours to reach Morioka from Tokyo, Support bolt: D25, L = 4 m x 34 sets/m and I could only imagine how long it would take to Lining concrete: t = 30 cm Spray concrete on upper half of tunnel: t = 25 cm (Silica fume content: 5%) drive.