Karori Tunnel after the earthquake-strengthening work
We completed essential earthquake-strengthening work on the Karori Tunnel portals and nearby banks in 2013.
The tunnel was strengthened because a seismic assessment of the tunnel showed that the portal walls at the tunnel entrances and nearby slopes were likely to suffer significant damage in a major earthquake.
This work is part of the Council's ongoing programme to strengthen important transport routes and earthquake-prone structures.
Karori Tunnel was built in 1900 and is Wellington's oldest road tunnel. Linking Karori with Kelburn and the city centre, it is regularly used by motorists, pedestrians and buses. Around 114,000 vehicles pass through the tunnel each week.
The tunnel is 76m long, 7.71m wide and 5.8m high. The Wellington Fault lies within 20m of the eastern (Kelburn-side) tunnel entrance.
What’s been done
The Karori Tunnel work included:
- rebuilding both portals and securely attaching them to the hillside
- constructing a new sprayed-concrete retaining wall along Glenmore Street on the Kelburn approach to the tunnel
- recreating the tunnel's historically significant facade and plaques
- building a new, low retaining wall on the other side of Glenmore Street next to the footpath
- applying an anti-graffiti coating to both portals
- repainting the inside of the tunnel
Fourteen new rock anchors, between 12 and 25m long, now secure the tunnel entrance to the hillside on the Karori side. On the Kelburn side, 21 rock anchors were drilled and concreted into position, to make sure the new portal and buttresses don’t come away from the hillside in an earthquake.
During the year-long project, the four old buttresses (on either side of the tunnel entrances) were demolished and replaced with strong new ones that were built on site behind scaffolding and screens. New pre-cast concrete portal arches were craned into position in sections on both sides of the tunnel and new portal walls and capping beams constructed.
The new retaining wall on Glenmore Street is secured to the hillside with 160 12-metre-long steel rods.
To see details of the anchored buttresses, capping beam, portal walls and retaining wall:
Drawings (172KB PDF)
The project began in late February 2012 and the structural work was completed in late February 2013.
News - Tunnel Works Coming to an End - 10.12.12
Work took a little longer than originally expected because of unforeseen ground conditions and a slip above the tunnel on the Karori side in October. Before planned concreting work could continue, engineers had to investigate, design and construct a new retaining wall – work that was not part of the original project.
The Council's priorities have been to complete the job safely and minimise disruption to traffic, bus services, pedestrians and cyclists.
News - Making Karori Tunnel Stronger - 02.07.12
The Council is looking at ways to address water seepage and drips in the tunnel and a trial is under way to test a couple of different sealants. Depending on the results and other city priorities, money may be set aside in the future to control water infiltration.
Council Contact Centre
Phone: (04) 499 4444