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Grouting underway at flooded Perth tunnel

Grouting is to the begin at the cross tunnel passage which was flooded by a leak between two Forrestfield-Airport Link tunnels in Perth, Australia.

The leak was discovered in a cross tunnel passage between the twin-bored tunnels on Saturday 22 September. A sinkhole developed immediately above the site.

At the time the TBMs were stopped and work had been continuing to stop ground water from leaking into tunnel one. An image of the flooded Perth Metro tunnel was posted online shortly after it was reported.

In an update, Forrestfield-Airport Link said that activities are continuing to repair damage caused by a leak in the project’s first tunnel-to-tunnel cross passage. 

“The next stage of works will involve compaction grouting. This is a ground improvement technique where grout is placed in the ground to reinforce the soil and fill any voids, and then compacted.

“Ground stability assessments will be conducted at regular intervals, followed by the repair and reopening of Dundas Road.”

According to Forrestfield-Airport Link, jet grout was injected into the ground late last year in preparation for the cross passage to be constructed.

Last month documents from Perth Public Transport Authority (PTA) director Ross Hamilton suggested that contaminated land issues could add up to AU$320M (£174M) to the cost of the tunnel project, and earlier this year, both boring machines were stopped for about eight weeks due to ground disturbances detected in the area.

The AUS$1.86bn (£1.03bn) Forrestfield-Airport Link is jointly funded by the Australian and Western Australian governments and will deliver a new rail service to the eastern suburbs of Perth – with three new stations at Redcliffe, Airport Central and Forrestfield.

The line will spur off the existing Midland Line near Bayswater Station and run to Forrestfield through twin-bored tunnels. In April 2016 the Public Transport Authority awarded the design, construct and maintenance contract to Salini Impregilo and NRW Joint Venture. The project is due to be completed in 2020.

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