So was Northern Link two billion cheaper – New Technology

In late November, opening the first phase of the Northern Link in Stockholm – well ahead of schedule. Building technology that is new in Sweden have helped to keep costs down.

The first stage, ranging from Northgate and Frescati to Darkness, covering about four miles down the road and goes mostly into tunnels. The stage is completed about a year earlier than planned and cost about 2 billion less than previously estimated.

The main reason for the reduced cost is the change in the law that made it possible to dig with traditional cut and cover technologies by Bellevue Park. Without the amendment had park surface had to be left untouched, and an expensive method where the pipe is pushed through the gravel ridge would have been used instead.

– We’ve probably saved a billion of the change, says Lars Lilja, Finnish Transport Agency project manager for Northern Link.

But also two structural engineering solutions which is unusual in Sweden have helped to keep down costs: sekantpåletekniken and inklädningsmetoden.

Sekantpålar is cast in situ concrete piles that can be used to creating retaining walls at the shaft. The method used in the two contracts at Northgate and trenches were excavated then remove with traditional cut and cover technology.

But sekantpålar also used with the more spectacular top-down approach in the construction of 200m concrete tunnel adjacent to Bellevue Park (see graphic). With this method, cast the tunnel from the top down.

The advantage became a simple routing of traffic on Roslagsvägen, held open during construction.

The method chosen by the builders Züblin and Pihl when the trial runs with sheet pile showed that the gravel ridge many large boulders would lead to problems. But even sekantpåletekniken had difficulties with the blocks.

– It took a little more time and more time was spent on maintenance, Jan-Erik Andersson, construction manager at the Swedish Transport Administration.

This method is common abroad but have not previously been used in Sweden since sekantpålar has not been approved for permanent structures . During the construction of the Northern Link, the regulations and Jan-Erik Andersson therefore believe that the method will gain ground.

To seal the Northern link tunnels against infiltrating water also has a new inklädningsmetod used. In mountain tunnels usually mounted dränmattor covered with shotcrete where water leaking in, but the Northern Link is instead a plastic sheet spanned.

– With dränmattor takes time and tend to clog, so water has a tendency to shift. Here we have a permanent umbrella that will always give a dry conditions, says Lars Lilja.

The water leaking from rock to drain along the outside of the fabric down the drain. The method is relatively common in Norway and the concept of the Northern Link was developed by the Norwegian builder Veidekke.

Transport Administration thinks that the method has worked well .

– Partly construction industrial, partly because it is predictable how long it takes. It makes identical throughout the tunnel system and it goes fast and fast, says Lars Lilja.

Transport Administration estimates that inklädningsmetoden saved “a few hundred millions “and sekantpåletekniken at Roslagsvägen SEK 40 million.

Follow New Technology on Facebook!