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Norra Länken, Contract Sections NL 35 and NL 51

Norra Länken (North Link) forms the northern part of a planned motorway ring around the centre of Stockholm. The scheme is altogether 5 km lang. Together with its Swedish partner Ode Hochtief is tackling contract sections NL 35 and NL 51. NL 35 consists of two tunnels each with two driving lanes. The tunnels are to be produced by mining means using drill+blast. The cross-section changes on account of special driving lanes; that are needed. Altogether 420,000 m³ will be excavated to create the 2 x 1,200 m long structure. The driving sections are located in stable granite. Fault zones are secured by anchors and steel fibre reinforced shotcrete. Advance grouting is undertaken to provide a seal against underground water. Furthermore extensive follow-up grouting is called for. The tunnel is to be provided with a novel kind of inner support something that is also new for Sweden: shotcrete is placed on tensioned sealing foil. By installing a precast part a cavity is created, which subsequently is used for instance as an emergency and maintenance exit. In contract section NL 51 Norra Länken returns to ground level. A 350 m long concrete structure with two tunnel tubes links up with tunnel section NL 35. As the depth decreases it forms a ramp, which finally brings back the route to ground level after roughly 370 m. The tunnel and trough are produced by cut-and-cover protected by an excavation pit. Altogether 210,000 m³ of excavated material will have to be removed. Up until the rock zone the pit is to be secured using 10,000 m² of back-anchored sheeting, then by jet grouting in the transition zone underneath and by a sealing screen in the rock. In order to be in a position to excavate the pit, railway tracks, which cross the planned route at the transition between NL 35 and NL 51, have to be relaid on a temporary ancillary bridge. In addition to producing the tunnels in their carcass state, evacuation paths, transformer and pump stations, the ventilation system with fans and ventilation shafts as well as roadworks and furnishing the tunnels represent parts of the project.

 

  • Country: Sweden
  • Region: Stockholm
  • Tunnel utilization: Traffic
  • Type of utilization: Road Tunnel
  • Client: Vägverket Region Stockholm
  • Consulting Engineer: Ramböll Sverige AB
  • Contractor: Hochtief Construction AG/Oden
  • Main construction method: Trenchless
  • Type of excavation: Drill-and-blast
  • No. of tubes: 2
  • Tunnel total length: 2,400 m (NATM), 720 m (cut-and-cover)
  • Cross-section: 180 m² (Standard cross-section)
  • Contract Volume: approx. 137 mill. euros
  • Construction start/end: January 2008 till December 2012