New columns and a reinforced concrete beam on the Karori side of the tunnel have been constructed. Sixteen rock anchors have also been installed to secure the steep slope above the portal, and cracks in the existing retaining walls have been repaired.
Councillor Chris Calvi-Freeman, Wellington City Council’s Transport Strategy and Operations Portfolio Leader, says work originally due to be finished by the end of June has been extended to mid-September.
“The strengthening work is taking longer than expected as our engineers found variable ground conditions behind the portal walls, which needed further investigation and redesign. The limited availability of specialist subcontractors following the Kaikoura earthquake led to more delays. We’ve got extra resources now and expect to complete work by mid-September.”
The work will make the tunnel’s portals and adjacent retaining walls stronger and more resilient, similar to the works carried out on the Hataitai bus tunnel and the Karori Tunnel in recent years.
The work is part of the Council’s ongoing programme to strengthen and protect key structures and transport routes, including tunnels, bridges and retaining walls.
Work hours are Monday to Saturday, 7am to 6pm. The tunnel will operate in both directions but will be reduced to one lane at times during the day. To minimise disruption at busy times, two lanes will operate during peak hours (Monday to Friday, 7am to 9am and 4pm to 6pm).
During working hours, members of the public are requested not to park in the area, including the wider berm/car parking at the corner of Northland Tunnel Road/Northland Road on the western side of the north portal.
The Council has contracted Fulton Hogan to do the work.
The tunnel was built in 1927 and is listed as a heritage structure in our District Plan. Changes planned will be in keeping with the existing design.