Tunnel grubby but sound, says NZTA

ABBIE NAPIER
Last updated 05:00 18/06/2014
Lyttelton tunnel
Stacy Squires/Fairfax NZ

SEEPING: The state of the Lyttelton tunnel is concerning users.

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The tiles in the Lyttelton Tunnel are falling off and water mixed with volcanic ash is seeping through the concrete walls.

The suspended tunnel ceiling is weak in places and the tunnel tarmac is beginning to lift due to water leaking under the road.

These are the main post-quake problems facing the Lyttelton Tunnel.

NZ Transport Agency regional performance manager Pete Connors says the tunnel is structurally sound and none of its problems are serious.

The techniques used when the tunnel was built 50 years ago would not be used now, he says.

The tunnel is made from unreinforced concrete sections sitting directly against the dirt walls. Each section is joined by "soft wood", with no waterproofing.

There has always been water leaking into the tunnel through the concrete and the joins. Before the quakes, the cleaning programme made it less visible.

Connors says subterranean shifting of the hillside has meant more water seeps through, mixed with dark, unsightly ash deposits.

"There is just more water getting through now," Connors says.

"There is movement in the joints, but it's not significant and it doesn't mean it's structurally unsound."

The water is also causing problems beneath the tunnel, where it is working its way underneath the tarmac and causing it to lift.

The tiles are beginning to lose their adhesion and fall off the ceiling. Cracks have appeared along the walls.

Tiles would not be used in tunnel construction these days, and work had been done to forcibly knock loose tiles off the ceiling to ensure none fell on unsuspecting motorists.

They will eventually need to be removed.

Connors says the water situation would eventually have to be dealt with, but plans were not yet finalised. At the moment, there is no urgency.

"You can't go over-reacting to water," Connors says.

A weakness in the centre of the ceiling only affects those working inside the ceiling cavity above and is not a concern for motorists below.

Increased load on the tunnel due to the closure of Sumner Rd and Evans Pass Rd means the tunnel is looking worse than usual.

Cleaning is second priority to keeping heavy vehicles moving through the tunnel.

About 1660 heavy trucks drive through to the Lyttelton Port and back every day, with dangerous and over-sized loads requiring long tunnel closures every night.

Because the cleaning machines require a clear tunnel, cleaning can often be delayed in favour of keeping traffic moving.

An agency spokeswoman says the tunnel is being swept twice a week, with a full clean happening once a month, as before the quakes.

However, cleaning could sometimes only occur in the first week of one month, and the third week of the next.

"It's not as clean as we'd like it to be," Connors says. "Rightly or wrongly, we've made the decision that cleaning of the tunnel is not a priority at the moment."

The ventilation system was still working normally and air-quality tests inside the tunnel were both within national guidelines, Connors said.

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- The Press

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