Amsterdam - Digging a Subway

Innovative mirror monitoring method intended to minimize disruption to street traffic

AMSTERDAM, Netherlands -- Seventeenth-century masons built Amsterdam on a foundation of wooden poles planted in soggy, sandy ground, leaving behind a beautiful architectural museum _ but one with walls prone to sinking or crumbling without warning. So how do you dig a subway under it?


The solution: 7,000 mirrors hung in clusters of three on buildings along the 2.4 miles of the route that's underground. 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. A millimeter is the thickness of a paper clip.

The system, unique on such a large scale, has already told townspeople something they may have guessed but couldn't know for sure: that theirs is a city in motion.

Soggy Amsterdam's Test: Digging a Subway - washingtonpost.com
SpringerLink - Book Chapter
Fibre Optic Sensors - Instrumentation and Monitoring Projects