Essential earthquake strengthening work is almost complete
Work on the city side is also going well and should be finished by the end of January.
As well as building a major new retaining wall on the Kelburn approach to the tunnel, the upgrade has involved replacing both tunnel portals, which were earthquake-prone. Some 200 holes have been drilled and long steel rods inserted and concreted into position to securely anchor the new tunnel entrances and wall to the hillside.
The tunnel, built in 1900, is the city's oldest and is used by about 114,000 motorists a week.
Project Manager Faiz Tawfeek says the project is part of the Council's long-term programme to seismically strengthen and protect important city transport routes and has made the route to and from Karori considerably safer.
"We expected to finish the work before Christmas but some unforeseen ground conditions and a slip above the western portal in October delayed things," he says.
"We had to clear the slip, investigate, and design and build a new retaining wall - which wasn't part of the original job - before we could complete the concreting work below."
From late January, both lanes in the tunnel are expected to be operating 24 hours a day.
The Council has been working to make the city more resilient to earthquakes. Major strengthening work has been carried out on Ngaio Gorge Road and Churchill Drive to secure an alternative route out of the city. We've also been building new retaining walls, upgrading reservoirs and replacing older water pipes with newer, more resilient pipes.
Karori Tunnel is close to the Wellington fault line and is the first tunnel to be strengthened.
We will look at what needs to be done to the Hataitai bus tunnel next and then the Northland and Seatoun tunnels.
Once work on Karori Tunnel is complete, Greater Wellington Regional Council will be working in Northland Tunnel Road and Raroa Crescent for about six weeks. It will install a new emergency water supply pipeline, which would be used after a major earthquake to supply water to parts of Kelburn. Traffic will be down to one lane at times on these streets but the work shouldn't affect Karori Tunnel traffic.
Parts of Chaytor and Glenmore streets will be resealed once work on the pipeline is complete.