TBM completes first Amsterdam Metro drive
TBM completes first Amsterdam Metro drive Jul 2010
Shani Wallis, TunnelTalk
It is only 12.5% of the TBM tunnelling needed, but completion of the first TBM drive for construction of Amsterdam's new North-South Metro Line earlier this week is a milestone. The initial 720m drive by the 6.83m diameter Herrenknecht Mixshield from the working shaft in front of the city's main Centraal railway station to the first underground station box at Rokin passed close to the foundations of important historic city buildings - among them the 'Beurs van Berlage', the old Exchange building designed by Berlage, and the famous Bijenkorf department store - and all is well.

The Bijenkorf department store is unscathed

Settlement due to ground movement and volume loss as the TBM progressed through the soft saturated soils of the canal city did not materialize and the buildings have been spared the structural damage that has occurred to buildings adjacent to open cut station boxes on the line and more seriously on earlier open-cut metro lines.
As well as tight control of the slurry Mixshield excavation, the operation and protection of the buildings was supported also by an extensive installation of compensation grouting arrays. In conjunction with a long established program of geo-monitoring and survey instrumentation on the ground surface and walls of the buildings to warn in real time of any excessive movement, the drive was completed without serious cause for concern.

North-South Metro route beneath Amsterdam

The TBM has arrived at the outside of the slurry end-wall of the Rokin station box and this is where it will stop. The station is not ready for a TBM break-in, so the excavation chamber has been filled with mortar and the components of the machine will be removed and rebuilt into the second shield for the parallel drive, leaving the shield and cutterhead abandoned in the ground. Once excavated, the tunnel junction will be executed from the station box with the cutterhead, backfilled excavation chamber and bulkhead broken out as part of that process.
The second TBM is expected to start excavating the parallel drive toward Rokin station at the end of August. Initially the plan was to use two TBMs for the total 3.2km of twin tube running tunnels on the 9.8km long North-South Metro Line, recovering both at the Rokin station box and relaunching them from the south end of the alignment for excavation of the tunnels north also to Rokin station.
However, due to serious ground loss, delays and settlement damage to buildings adjacent to the Vijzelgracht station box on the line, it has been decided to use four shields on the project, two from the launch pit to Rokin station for the first two, and two more for the two drives from the south launch box north to Rokin station.

Settlement damage at the Vijzelgracht station box

For the first two short drives the components of the first machine have been retrieved and built into the second parallel drive shield with its new cutting head. In this way tunnelling could start without having to wait for completion of the stations.
The first machine took 90 days at an average 8m/day to complete the 720m drive. The drive was under intense political and social scrutiny, given the earlier problems, and that no problems were reported is a great relief to the project managers and administrators as well as to the construction consortium Saturn, comprising Züblin of Germany and local partner Dura Vermeer. Similar tight control of the Mixshields on the project's following tunnel drives will be needed to keep political support of the construction program.
TBM underway for Amsterdam Metro - TunnelTalk, April 2010

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