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The Wingatui rail tunnel is on track for some new tracks.
Kiwirail staff have recently been seen building what appear to be a set of tracks from a large pile of concrete sleepers at the old Wingatui rail-yard.
A Kiwirail spokeswoman said three sets of 75m lengths of track were being assembled at the yard to test the safest and most suitable process for replacing the tunnel tracks, which were scheduled for renewal.
Although the rail track only was due for renewal, it was decided to remove all the old sleepers while the work was going on, which also meant they could rebuild the track bed.
That would mean less maintenance was required over the next decade.
While the test tracks were being assembled now, the actual work in the tunnel would take place over four days in mid-May, when all of the track sets would be built and installed.
The work would involve replacing 705m of track and 1421 sleepers in the 896m-long tunnel.
No trains would be running on the track to Wingatui during the installation, except for work trains, which would be used to assist with moving materials, discharging ballast and finalising track level and position.
Some work would be done before the main body of works, including surveying, drainage, clearing outside of the tunnel, material relocation and shaping inside the tunnel, and the cleanup would take about a week afterwards.
The job would require heavy machinery, and a specialised fan would blow fresh air through the tunnel while men and machinery were working inside.
''There will be a certain degree of noise produced from the works as per any large scale civil works, but we will attempt to mitigate this as much as possible and keep our neighbours informed.''
Most of the heavy works would be either inside the tunnel or north of the tunnel where fewer people would be affected.
A letter drop would inform neighbours who might be affected, including the hours of work, she said.