Auckland rail: Western Line passenger services reduced after subsidence found

Passenger trains on Auckland's Western Line are running at a reduced timetable while KiwiRail urgently investigates subsidence on the line.

Only a single track will be operational as a precaution from Wednesday.

KiwiRail staff working on a routine inspection of the Western Line on Monday first discovered the subsidence issue when they found movement in an overhead electric pole.

Auckland Transport said it was working closely with KiwiRail to minimise disruption to passengers.

Train services were operating every 30 minutes between Swanson and New Lynn, with services between New Lynn and Britomart running every 20 minutes.

Passengers travelling through New Lynn in either direction will need to transfer between trains at New Lynn.

KiwiRail was carrying out investigations to confirm how soon work could be completed to allow train services to resume normal service, Auckland Transport said.

KiwiRail capital projects and asset development chief operating officer David Gordon told Midday Report geotechnical specialists discovered a slip which caused cracks in the bank below the rail corridor.

They also found a few sections of a concrete retaining wall below the rail line had moved.

There was no immediate risk posed by the slip but train speeds were reduced in an abundance of caution, he said.

"The risks are basically that the ground keeps on slumping and that starts to make the tracks sink or slump on one side."

However, if this subsidence was to continue it was likely to occur over an extended amount of time, he said.

Weekly inspections of the track meant the slip had likely only occurred within the last day or two, he said.

In a statement on Wednesday afternoon, KiwiRail rail operations chief operating officer Siva Sivapakkiam said initial assessments appeared to indicate the ground was the root cause of the issue.

"We are continuing to monitor the ground in the area for any further movement."

Over the next few days, KiwiRail will try to work out the scale of the slip and what options were available in the short term to reopen the line safely.

"Once the underlying condition of the ground is better understood, KiwiRail can then progress with design and planning work for a full repair," Sivapakkiam said.

KiwiRail said this problem was to do with the ground and therefore not linked to its Rail Network Rebuild project to replace ageing foundation, which was also set to shut some lines over the coming years.