Northland Tunnel strengthening

From January 2017 to February 2018, we completed earthquake strengthening work on the Northland Tunnel entrances and adjacent retaining (wing) walls.

Strengthening work being carried out at Northland Tunnel.

Northland tunnel

Resize

What we did

  • built new retaining walls on the Northland side in front of the two existing retaining (or wing) walls that are on either side of the tunnel entrance
  • constructed a new reinforced concrete beam behind the top of both tunnel entrances which will help secure the portal to the underlying rock
  • enlarged the two existing vertical buttresses on the Karori side and secured them to the hill with long steel rods called rock anchors
  • cleared vegetation and built three new buttresses on the Karori side in front of the existing retaining wall to the right of the tunnel entrance
  • drilled and installed 36 rock anchors
  • repaired cracks, plastering and repainted the tunnel entrances
  • planted the banks above the tunnel.

Background

The tunnel was built in 1927 and is listed as a heritage structure in our District Plan.