The Mt Victoria Tunnel upgrade project has just passed a major milestone with the final demolition of the tunnel's suspended plenum ceiling.
The plenum was built with the tunnel in 1931. It formed part of the ventilation system and carried some of the tunnel's services. It was made of concrete and steel, and suspended from the tunnel's roof and walls. It had been reinforced in the 1970s, but recent inspections had shown it was deteriorating and needed to be removed.
NZTA State Highway Wellington Manager Rod James says that the demolition has gone exceptionally well.
"Refurbishing working tunnels isn't something we've done before in New Zealand, so the NZTA has worked closely with the Wellington Tunnels Alliance to develop a comprehensive plan tailored specifically for Mt Vic. A special hopper was built to catch the falling concrete and protect the tunnel's fittings as demolition progressed. A removable safety platform was installed under the ceiling to catch any falling debris that might prevent reopening of the tunnel. It also protected the public using the road or walkway while the tunnel was open.
"As it turned out, it took much more effort to demolish the ceiling than the reports had indicated and there were no reported instances of debris falling onto the safety platform. We're very pleased with this result."
The tunnel upgrade also includes new fire safety equipment, including a high capacity water deluge system and heat detection system. Road works at the Hataitai end of the tunnel to install a new water main are nearly complete. Work on the tunnel is scheduled for completion in the second half of January, and testing and commissioning of the systems to be finalised in March 2012. Overnight closures will continue until that time.
"The Mt Victoria tunnel is a vital part of the local transport network, so it's important that we undertake this work with as little disruption as possible," says Mr James. "We appreciate the patience and understanding that the public have shown and we're working as quickly as we can to complete this necessary upgrade."
The Mount Victoria Tunnel and Terrace Tunnel upgrades are part of the Wellington Northern Corridor Road of National Significance, aimed at improving safety, supporting economic growth, and easing congestion.