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Ground monitoring on a grand scale in Amsterdam

NEWS

ONE OF Europe's largest and most automated ground settlement monitoring contracts began last month in Amsterdam.

The contract is aimed at recording - and possibly reducing - any structural damage caused by tunnelling for the city's new metro system.

Over the next six years more than 150M readings will be taken of movements at 2000 'at-risk' city centre buildings as twin tube tunnels are driven through soft alluvial clays and sands just metres from their timber piled foundations.

'The ground here is so weak that many central buildings have already settled to some degree, ' said Christophe Bourlart, operations manager for monitoring contractor Soldata.

'Our job is to carry out an extensive settlement survey of the route both before metro construction starts and during its two-year tunnelling phase.'

French based Soldata, a subsidiary of geotechnical contractor Soletanche Bachy, is working in joint venture with Dutch company Grontmij. More than 70 measurement stations with computer controlled theodolites will continuously read 5300 targets placed on suspect buildings within 100m of the tunnelling route.

The £9M contract will later include measuring ground movement just beneath the surface along the full 3.4km length of tunnelling as well as checking stability of 50m deep diaphragm walls forming the sides of the four main cover and cut station boxes.

Initial tender bids to complete all the metro's underground works as a single contract proved too expensive and the project is now being rebid as separate contracts for tunnels and stations.

By the time tunnelling starts in 2004 it is hoped that a full face boring machine, able to compensate for settlement, will have been developed and be able to use the Soldata readings to help minimise surface movements.

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