Vol. 35 Winter 2005

Tokyo is one of the world's most densely populated cities. Seen from a highrise building, Japan's capital is a sprawl of buildings that extends into the suburbs as far as the eye can see. However, even in this overcrowded metropolis, a vast, unutilized underground space is being exploited in a socially and environmentally beneficial way. In this article, we showcase a new expressway being constructed beneath central Tokyo.

The cross-section of the Tokyo Metropolitan Expressway Central Loop Shinjuku Line

Traffic Problems Continue to Plague Tokyo The Tokyo Metropolitan Expressway system carries more than 900,000 vehicles each day, and traffic congestion is a chronic, exasperating problem for busy commuters. The average speed on surface roads in Tokyo is only 20 kilometers (12.5 miles) per hour, and easing traffic congestion is an urgent task for the metropolitan government. However, as countless commercial buildings and residences stand next to Tokyo's narrow streets and roadways, the widening of existing roads is filled with difficulty. Not only that, opposition to new road construction is deeply rooted among residents of the capital, who worry about the effects of noise and air pollution created by the new traffic. One answer to the problem of traffic congestion that is drawing widespread attention in Tokyo is expressway construction that utilizes underground space. It is comparatively easy to secure construction sites for tunneled expressways, and underground motorways offer environmental benefits including the preservation of neighborhood landscapes and the facilitation of noise pollution and exhaust control.

Construction of the Central Loop Shinjuku Line One example of an underground expressway planned as a solution to the chronic traffic jams in central Tokyo is the Central Loop Shinjuku Line, part of the Tokyo Metropolitan Expressway system. The eastern half of this expressway is already open to the public, and construction of the Shinjuku Line, which will connect bustling commercial districts Ikebukuro, Shinjuku, Shibuya, and other city sub-centers in western Tokyo, is progressing. The most important characteristic of the new expressway is the construction of two 13-meter (43-foot) wide tunnels, over 30 meters (99 feet) deep, that will stretch almost the entire length of an 11-kilometer (seven-mile) section of the expressway. According to Metropolitan Expressway Co., Ltd., completion of the Central Loop Line will dissolve up to about 60% of the congestion on its expressways, and traffic congestion relief is expected to reduce carbon dioxide emissions by about 25,000 tons per year. For these reasons, early completion of this key central city traffic artery is expected to enhance urban functionality and reduce the environmental load.

Underground Expressway Construction Let's examine the process by which full-width expressways are constructed 30 meters (99 feet) underground. Kajima is excavating the Matsumizaka-Yoyogi Tunnel section of the Central Loop Shinjuku Line using the pressurized slurry shield tunneling method, by which the cutter head of the shield machine is placed at the head of the tunnel site and rotated to excavate the tunnel. Inside the tunnel, ring-shaped blocks called tunnel segments are assembled to form the tunnel ringed liner. The shield machine used for excavation ranks among the world's largest; it has an outer diameter of 13 meters (43 feet) and weighs about 2,500 tons. The machine is operated and controlled from a central control room inside the existing tunnel, and the shield is capable of continuously tunneling a construction sector 2,660 meters (8,700 feet) in length. Concrete, steel and cast-iron tunnel liner segments transported to the shield machine are assembled one after another to form the circular reinforcing tunnel walls. Massive amounts of earth and sand are removed in this process, fully 300 tons for each ring tunneled. The excavated mud is dewatered at a slurry treatment plant, and the remaining soil is transported to a landfill. As an antipollution measure, the resulting wastewater is treated by the tunnel excavation system, which is equipped with a water treatment facility before being discharged as sewage.

Kajima's shield machine is ready to start the digging.

Toshiharu Tanaka, P.E., Project Manager of the Matsumizaka-Yoyogi Tunnel project, comments, "When a problem occurs at the worksite, even if we rack our brains to come up with a solution, things don't always go as planned. At such times, we must be forward-thinking and enthusiastic in rising to the challenge of devising workable solutions. If we can't accomplish this, we can't create good products." Currently tunneling is 70% complete, and steady progress is being made toward the goal: the Matsumizaka vertical shaft.

Segments are stocked inside the tunnel. New DRC segments were applied.

New Deep Underground Road Network Planned In 2000, the Japanese government enacted the Law for Special Measures Concerning the Public Use of Deep Underground Space. This law has made it possible to use deep underground space 40 meters (130 feet) or more below ground for public works without the reconciliation of land rights or payment of compensation in advance, and as a result new construction projects are being implemented. Kajima will take full advantage of technologies for excavating tunnels deep underground, technologies for constructing underground interchanges, and other critical technologies perfected over the years as well as construction methods and materials developed to minimize costs as we seek solutions to problems associated with constructing a new expressway network deep beneath the cities of Japan.

Tokyo Tunnelix On October 14 and 15, 2005, a unique event was held at the Matsumizaka-Yoyogi Tunnel job site. The event drew a large press corps and 300 lucky guests selected by lottery. The first day of the event featured a remarkable underground fashion show named "Spirit of Engineer," at which Bernhard Willhelm, a fashion designer who shows his collections in Paris, unveiled new fashions inspired by Japanese construction worker uniforms. Construction workers from the site took turns on the catwalk on a specially constructed stage and modeled the new fashions. "Tunneling Technos," an exhibition of numerous cutting-edge technologies used for the Central Loop Shinjuku Line tunnel construction project, was held on both days of the event. The guests were overwhelmed by the immensity of the tunnel space and thoroughly enjoyed their thrilling experience of the underground expressway in progress.

Vol. 35 Winter 2005 A New Expressway Takes Shape beneath Central Tokyo Kajima around the World

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