KiwiRail's project to repair and replace tracks around the Auckland Metro network is ramping up with the arrival of a grinder machine to re-surface worn rails.

Grinders are commonly used to maintain tracks by smoothing out the railhead surface and correcting its shape, thereby extending the lifespan of the rails.

KiwiRail has identified about 100km of rail within the Auckland network that urgently needs repairing and replacing. Teams have been brought in from around the North Island to get the job done and have been focusing on new rail while awaiting the arrival of a grinder from Australia, which is now ready to start work.

"Our goal is to create the best track conditions to match train wheels and to reduce damage and fatigue caused by rolling contact between wheels and rails," says KiwiRail Chief Operating Officer Todd Moyle.

"Our focus is to get this project completed as quickly as possible with minimal disruption for passengers.

"Grinders travel at 3km per hour and the work will be carried out at night. We know this may, unfortunately, cause some disruption for our corridor neighbours and we apologise in advance for this."

A typical 300m long curve will take about an hour and half to complete and a turnout will take around two hours.

"The work we do now means we have better control over fatigue cracking that may occur," Mr Moyle says.

To prevent the same problem re-occurring, a more intensive maintenance plan for Auckland's rail network will begin once the current remediation programme finishes early next year.

"When we regularly use the grinder we can increase the life of the rail, and on our busiest lines we need to grind about every 3-4 years."

Additional machines will arrive in November and December to accelerate the Auckland metro grinding programme.

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