Amsterdamned: Building a subway in the underground city
Amsterdam is known for (ahem) a few things by tourists, but should travelers let the smoke clear and turn off the red light for a moment, they might see parts of the city they'd otherwise miss. One of the lesser-known realities of the city on the Amstel is that its beautiful canal houses and intricate waterways are actually below sea level (at least at high tide). The city is also largely built on a foundation of wooden poles. Four hundred year old wooden poles, at that.
Sounds like the perfect city to build a subway in, doesn't it? Yes, you heard right--a few years ago Amsterdam's politicians decided to build a subway.
Construction of a new "North-South" line for this city of canals and rivers began in 2003, and is presenting Dutch engineers, famed for their ingenuity in keeping this waterlogged nation dry, with devilish challenges.
"The politicians told us: 'We want a subway, we're prepared to pay for it and accept some disruption, but the one thing we absolutely don't want is any damage to the city,'" said Johan Bosch, the project manager. "We need a system so that if things don't go as expected, we don't find out after the damage is irreparable."
Measuring devices shine infrared beams onto each mirror once an hour, measure the reflection, and feed data into a central computer.
After triangulating, the computer raises the alarm if any building shifts more than 0.5 millimeters in any direction.