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Steady state
22/10/03
A major ground settlement monitoring contract is underway in Amsterdam a full year before the city starts building its underground metro. David Hayward visited the Dutch capital to find out why

Tree surgeons in Amsterdam are busy pruning trees along the city’s central boulevards armed not with chainsaws but scissors and laser beams. Wind movements and seasonal growth are crucial factors as branches are carefully removed at night during an operation likely to spread over six years.

Nearby, discussions are continuing with local police to reposition a street banner warning of pickpockets.

These two seemingly bizarre operations have an equally unusual common aim: To build the city’s underground metro system without damaging any of the 1600 historic buildings close to its tunnelled route.

To achieve a goal of negligible settlement, in a city where most old buildings subside naturally in the weak ground by an average 1mm every year, demands the pioneering teamwork of surveyors, tunnel machine manufacturers and computer software whizkids.

Ground and building settlement monitoring – an operation involving over 70 automated theodolite work stations, plus 3000 other instruments producing, over six years, a staggering 150M readings – is already underway. And design work has started on an ‘intelligent’ tunnel boring machine capable of interacting with three dimensional computer analysis of surface movements during tunnelling to both predict and minimise surface settlement above it.

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