With 27 million residents, Tokyo is both the world’s most populous metropolis and, in many places, one of its most densely packed. That leaves little room for further expansion; already the average commute time is 56 minutes, with some salarymen traveling like sardines on local trains for as long as two hours. The solution? Build down instead of up. “To me it’s obvious that, in Tokyo, we have no choice but to go underground,” says Nobuyuki Takahashi, an engineering professor at Waseda University. “We have been studying the possibilities of deep-underground space for nearly 20 years.”
Those plans are picking up steam. During the go-go 1980s, firms began drafting schemes to create underground cityscapes replete with office buildings, sports clubs, roadways and rail links–even gardens. Most of those plans were stalled by the economic doldrums of the 1990s, Japan’s lost decade. Yet neither recession nor tumbling land prices has entirely squashed the idea. In 2001, lawmakers passed legislation that legalized “deep underground” development beneath the country’s major cities. The zone, more than 120 feet belowground or 30 feet beneath existing buildings, is now open to public-works projects free of charge and without prior permission from landowners on the surface. “The discussion grew kind of quiet for about 10 years,” says Hideki Murata, a manager at the government’s Deep Underground Utilization Plan Office in Tokyo. “Now we are finally able to take advantage of the underground space we need.”
The focus today is on burying infrastructure in order to free up space on the surface. The objective: to craft a landscape rich with promenades, bike paths and gardens to form a natural veneer above the “guts” of the city. The idea isn’t new, to be sure, but Japan hopes to implement it on a heretofore untried scale. Tokyo’s topography will remain one of clustered towers. But many surface roads will turn to green belts, railway lines will disappear into tunnels and major urban systems, everything from dumps to gas-storage tanks, will move deep underground–and all by the middle of this century.
The path to Tokyo’s future is anything but glamorous. It winds through a construction yard in suburban Kanagawa prefecture, disappears into a circus-tent-like warehouse and descends 150 feet down an elevator shaft to Tokyu Construction’s Sub-Terranean Urban Development project. Dug in 1989 at the cost of $100 million, it penetrates a geological formation known as the mudstone layer, a thick stratum of soft bedrock with properties ideal for building tunnels and caverns. Initially the object of gee-whiz promotions–including schoolkid photo ops and underground concerts–the classroom-size catacomb quickly lost Japan’s attention. Today its arched ceiling sprinkles ground water, forever dampening air that remains at a constant 64 degrees Fahrenheit. Visitors encounter a modest fern garden and a tiny goldfish pond.
Appearances aside, the site has yielded vital data on the dynamics of the mudstone layer and techniques for exploiting it. New insights into tunneling methods, concrete’s durability within the bedrock and ground-water management are among the pay-offs. Earthquakes deliver just a tenth of their surface impact at the site; deformation–the slow twisting and compressing of the bedrock observed in tunnels–is minimal. In contrast to undersea construction, where water pressure increases with depth, ground pressure within the mudstone layer is actually less than in the stratum above it. “We have the capability to build cities up to 300 feet deep,” says Takakura. “The barrier isn’t technology, it’s the cost.”
Economics now will dictate the form Tokyo’s deep underground takes. Early this year Chikage Ogi, the construction minister at the time, voiced her support for Tokyo’s plans to jump-start a controversial freeway project by sinking it far below the surface. Frozen since the 1960s after not-in-my-backyard landowners blocked it, the 10-mile-long stretch of highway once threatened 3,000 homes and looked untenable at an estimated $1.1 million per every 3.3 feet to construct. But the underground version of the roadway would require demolition of only 480 homes and cost 30 percent less, according to official estimates. “We’d like to complete it as the first project under the [new] law,” Ogi said in January. Japan’s maglev–a proposed 300-mile-per-hour bullet train linking Tokyo, Nagoya and Osaka–is another test case. “This is the biggest project that could involve the new law,” says its main champion in Parliament, Liberal Democratic Party lawmaker Taizo Nozawa. “There’s nowhere else for it to go but deep underground.”
Professor Takahashi of Waseda has a less glamorous pet project in mind. “What we are thinking about is burying the city’s whole circulatory system,” he says, which boils down to moving waste out and energy in. Instead of street-level garbage collection, he has proposed an underground system that carries rubbish to the edge of the city to be burned in power plants–a scheme that might someday rid the city of diesel-belching garbage trucks. Private developers are now considering a “phase one” system linking areas of Tokyo’s main business district to a power plant on Tokyo Bay, with construction to begin “hopefully in a couple of years,” he says.
Tokyo is already breaking new ground. In 2000, the city christened a new subway line that runs 150 feet below the surface at its lowest point, brushing the upper edge of the area marked for “deep zone” construction. But riders soon discovered a predictable problem. Those exiting from downtown stations spent nearly three minutes on escalators moving from the subway platforms to the street–an eternity for commuters obsessed with shaving seconds off their trip to and from work. It’s no surprise–or coincidence–that Mitsubishi Electric Corp. has a two-speed escalator in development that could shorten the trip by a minute. In Tokyo’s urban underground, how quickly people can come up may determine how low they will go.
