Houses along new Amsterdam metro line construction site subsided

DutchAmsterdam.nl — Two buildings at Vijzelgracht, along the construction site for the new North/South line of the Amsterdam metro system, have subsided.

Shopkeepers in the buildings blame the construction work, while the metro project bureau simply says those buildings already had ‘bad foundations.’

The antique clocks store Veenendaal de la Haye, at Vijzelgracht 35, is now closed for renovation of its foundation. The building shows some cracks in the wall, and due to the subsidence windows no longer open.

This corporate movie produced in support of the new metro line includes a good explanation of the soil and foundation issues the project faced:

Patisserie Holtkamp at Vijzelgracht 15 also has cracks in the walls, but the store remains open. Work on its foundation will commence after Easter.

In June and September 2008 several monumental buildings at Vijzelgracht were seriously damaged as a direct result of construction work for a new leg of Amsterdam’s subway system. [See: Unstable Amsterdam is building a new subway line].

The City of Amsterdam should never have approved the construction of the North-South metro line a special city council investigative committee concluded last December.

In its report the committee also urged the council to debate the risks associated with the planned drilling of a metro tunnel underneath the historic city center.

Amsterdam’s sandy soil

Store owner Nico Veenendaal tells Amsterdam newspaper Het Parool he believes the wooden foundation pilings underneath his store and home have been damaged due to fluctuating groundwater levels as a result of the metro construction.

Amsterdam’s sandy soil is too soft to build on, which is why the city is built on piles driven deep into the ground until they reach a solid layer of rock or compacted clay.

Nowadays reinforced concrete piles are used, but the vast majority of buildings in the city’s historic center rest on timber piles.

Low ground water levels cause the tops of the pilings to fall dry and crumble.

Construction pits near buildings include a system of pumps and metal, water-tight dams designed both to keep ground water out of the construction zone, and to keep the level of ground water outside the pit at a safe level.

Several incidents of subsidence along the construction route have been caused by leaks in the dams.

Project Bureau: not every foundation problem our fault

Michiel Jonker of project bureau Noord/Zuidlijn comments in Het Parool that in this case we’re not dealing with subsidence, but rather the renewing of foundations. “It is not due to work on the North/South line that that groundwater fluctuates. It’s simply that these foundations are done with. Many properties in Amsterdam have a poor foundation.”

Jonker suggests you can’t blame every foundation problem on the North/South line, though the construction work does bring such problems to light.

The project bureau uses a unique measuring system, the largest of its kind in the world, to monitor subsidence problems along the metro contruction route (see video above).

Veenendaal says work on his property will take six to eight weeks. “They told me everything will be compensated.”

Angela Holtkamp of the patisserie says the foundation underneath the bakery, in the rear of the building, was treated some fifteen years ago. At the time she was told the foundation underneath the front of the building was good for another fifty years. “But now measurements show something needs to be done urgently,” she says, noting that you can’t complain about the new metro line as construction will continue regardless.

“Later we hope to benefit from it,” Holtkamp says.

Earlier this month the owners of Bijenkorf, Amsterdam’s most famous warehouse, asked the city to delay drilling for the metro underneath its historic building until further research into possible risks could be perfmed.

Their request was turned down.
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