North-South Line, Amsterdam CS

Over the past few years, the contractors have realised a building excavation below the middle tunnel of Amsterdam’s Central Station. To this end, they inserted large steel tubes with a diameter of 1.85 metres, to a depth of up to 65 metres below the hall’s passenger platforms.

Client:
City of Amsterdam, Service Infrastructure, Traffic and Transport
Location:
Amsterdam
Number of elements:
1
Immersion:
2011
Specials:
Under monumental station
Projecten - Amsterdam 002
CSO (14) [activity carr]
Invaren 2

Project

Working downwards from the station hall, the contractor made a so-called sandwich structure. Before starting on this operation, the workers transferred the load borne by the foundations of the station hall’s large corner towers to new steel piles. These piles were kept in place by a jack structure. Immediately after the excavation was completed, the team transported a tunnel segment from the IJ to the site, after which it was immersed. Following its immersion, the segment was suspended from the roof slab via an innovative system of hanging rods. Jack pressure levels in these hanging rods were continuously monitored during the flooding process.

Unique site

The tunnel has a total length of 136 metres and consists of a single immersed segment. This segment was transported from Amsterdam’s Westelijk Havengebied to the city centre via the North Sea Canal and the IJ. A unique aspect of this immersion operation was the site itself: the segment was immersed under the monumental hall of Amsterdam Central Station, with very little headroom to work in.

Client

The project was commissioned by the Municipality of Amsterdam, Department of Infrastructure, Traffic and Transportation, Projectbureau Noord/Zuidlijn.

Awards

Together with Strukton Immersion Projects ‘Mergor’, the Strukton/Van Oord consortium was proclaimed ‘Infrastructure Project Team of 2011’. They were honoured with this title during the NVDO Infrastructure Conference, winning both the event’s jury award and public award.

Survey Systems

The site around the to-be-immersed tunnel segment severely restricted the team’s opportunities to use ‘standard’ measurement systems. The team carefully considered the various systems available and their alternatives. Ultimately, they decided on a system of total stations and prism reflectors.

However, the limited headroom under Amsterdam Central Station did require some creative solutions.

Those interested could follow the progress of the immersion operation via http://www.geocon3d.com/

In addition, Geocon measured:

  • Tensile forces in the winches by means of sensor probes.
  • The supporting forces in the hydraulic jack rods during the immersion and flooding processes.
  • The water levels in the ballast tanks.

Innovations

After making a thorough analysis of the site and examining the opportunities to utilise different measurement systems for the positioning of the CS segment, Geocon ultimately opted for a proven method: immersion with the aid of total stations that measure angles and distances to prism reflectors in the mast and shaft. Shortly before immersion got underway, Geocon received a request to enable the remote monitoring of conditions in the tunnel. To this end, the team set up a website where the client can review the requested data in real time.

Due to the extremely limited headroom - a mere 2.5 metres from the watermark - the team were unable to use a traditional survey mast. They responded by developing a mast that collapsed during immersion. After iets functionality and reliability had been tested on the site parking lot, the mast performed flawlessly during the actual immersion.

Once the immersion operation had been rounded off, Geocon set up a web page at the client’s request that allowed for the continuous monitoring of the tunnel’s current status. The site presented data on water levels in the ballast tanks and excavation, as well as live video images from the tunnel itself.

The team also performed a successful test with water pressure gauges that calculated the loads at the segments’ hoisting points based on the pontoon draughts.

Animation enter and immersion CS element

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Preparation tunnelelement

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