Widely regarded as one of the most challenging infrastructure projects in Dutch history, the North/South Metro Line in Amsterdam will be officially taken into operation on Saturday 21 July. Witteveen+Bos, Royal HaskoningDHV and Ingenieursbureau Amsterdam collaborated on the project in a consortium called Adviesbureau Noord/Zuidlijn. During the design phase, the contract preparations and the supervision of the performance of work, the joint venture made a significant contribution to this technically complex project. The line connects North and South Amsterdam and is expected to transport approx. 121,000 passengers per day on average. This rapid metro line is essential for the economic developments of the metropole region of Amsterdam and its accessibility. It will help to combat traffic congestion and is expected to reduce car usage in the city centre – both key objectives of the city government.
Leading position in tunnel engineering
A key precondition in the design phase was the requirement to retain the historical character of Amsterdam’s city centre. At the start of the project in 1994, this meant that the underground metro line could only be realised if conventional construction methods were applied in a very creative manner. Existing methods such as bored and immersed tunnel construction and pneumatic sinking of caissons have undergone radical innovation to suit the unique circumstances prevailing in Amsterdam. By developing these innovative methods, the Dutch engineering and construction industry has now gained an even stronger leading position in underground construction, both domestically and internationally.
The North/South Metro Line is a complex project characterised by budget overruns, delays, difficulties in the political decision-making process and problems during construction. These issues sometimes eclipsed the wonderful technical achievements realised during the project.
New foundation below Amsterdam Central Station
The tunnels below the IJ river and Amsterdam’s central railway station presented one of the biggest challenges. Hans de Wit, managing director of Tunnel Engineering Consultants (TEC) and a project director at Royal HaskoningDHV: “The three prefabricated tunnel elements were 12 metres wide, 7 metres high and 141 metres long and were immersed in a dredged trench in the IJ river. A fourth 22-metre-wide, 8-metre-high and 130-metre-long tunnel element was immersed below Amsterdam Central Station, while daily train services continued as normal and thousands of passengers were transported to their destination.”
Stations more than 25 metres underground
The Adviesbureau engineers also demonstrated their capabilities during the construction of the underground stations at Rokin, Vijzelgracht and De Pijp. The tracks in these three stations are located far underground, at depths of 21.5 to over 25 metres. The stations were built using a special method based on diaphragm walls and grouting techniques, in some cases at a distance of just 3 metres from the historic facades of nearby buildings. De Pijp station has superimposed platforms at two levels, since the tunnel tubes cannot be located next to each other below the narrow Ferdinand Bolstraat without prior demolition. Demolishing buildings for the construction of the North/South Metro Line had been ruled out on principle, making the design and construction of De Pijp station particularly complex. Rokin station was excavated using innovative jet grouting techniques. At a depth of over 30 metres, the soil was reinforced using grout (a fluid form of concrete consisting of a mixture of water, cement and sand) to provide horizontal support for the walls, in order to minimise subsidence in the area.
Hans de Wit: “We gained unique experiences from the use of highly innovative techniques. As a result, we have further strengthened our leading international position in underground construction and I am very proud of that.”
Ground Engineering Award
The project won the prestigious Ground Engineering Award twice: in 2014 for the design of the bored tunnels and the special techniques used for that purpose, and in 2013 for the innovative techniques used in realising the ‘table structure’ and the immersed tunnel below Amsterdam Central Station.
Techniques used in the construction of the North/South Metro Line:
- Bored tunnel technique
- Immersed tunnel technique
- Cut & cover tunnels
- Pneumatic sinking of caissons
- Caissons method
- Compensation grouting
- Refrigeration technologies
- Vertically bored pile wall
- Fire safety engineering
- Shield transfer systeme