New rail bypass on track to replace 107-year-old tunnel in Marlborough

Tuesday, 8 September 2020

Tar Barrel Tunnel or Tunnel 21 will close from next year when the new rail bypass opens.

A $35 million KiwiRail project to shift a 1km section of track in Marlborough is in its final stages.

KiwiRail chief operating officer David Gordon said the construction of the Tar Barrel tunnel bypass, south of Ward, was on track and the new 1km section of rail line through a large earth cutting would open early next year.

At that time the quake-repaired Tar Barrel tunnel, also known as Tunnel 21, would be closed to trains.

“We’ve recently completed the cutting and have excavated about 420,000 cubic metres of [earth] material, most of which has been redistributed to neighbouring farm areas,' Gordon said.

“At the end of August, our contractors finished planting 10,000 natives across two hectares to the south of the Tar Barrel work site, using seeds taken from the area and grown in a nursery before being replanted,” Gordon said.

KiwiRail is undertaking a $35m project to shift a section of railway between Christchurch and Picton.

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The 167m long Tar Barrel Tunnel was built in 1913 and is the oldest tunnel on the Main North Line.

The tunnel bypass will be completed by early next year and the old tunnel will be closed.

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During construction of the rail bypass a temporary diversion was put in place for State Highway 1 traffic while a new road overpass was built. It is expected to be completed in the next few months.

“We should have a clearer idea of the timeframe for opening the new overpass in early October,' Gordon said.

Around 420,000 cubic metres of earth has been excavated for the project, most of which has been redistributed to neighbouring farms.

The 167m long Tar Barrel tunnel was built in 1913 and it is the oldest in the Main North Line.

In December last year Gordon said the tunnel lining was damaged during the 2016 earthquake. It had been repaired but a lot of work was still needed to bring it up to modern standards, which would cause considerable disruption.

“Its small size means trains must slow down to go through it, which lengthens journey times on the line and causes operational constraints,” Gordon said.

The small and curved tunnel was a safety risk for fast moving trains as trains had to slow down to 25kmh to go through the tunnel. Once work is finished trains will be able to travel up to 80kmh through the area.

“Bypassing the tunnel, which runs below SH1, allows us to improve rail operations and seismic resilience for both road and rail,” Gordon said.

The Picton to Christchurch 335-kilometre train trip, includes 22 tunnels and 175 bridges.

In 2018, Prime Minister Jacinda Ardern announced that the KiwiRail's Coastal Pacific passengers service would get a $40 million investment and would make it a year-round service.