At 1pm on September 22 a leak developed during cross-passage construction between the two 8km long, 7m diameter Forrestfield-Airport Link tunnels in Perth, leading to a sinkhole developing immediately above the site.Immediate efforts were made to stop the leak, which occurred in tunnel 1, and this continued throughout the night.

Despite these efforts, groundwater and silt still flowed into the cross passage and one of the tunnels. The sinkhole developed on Dundas Road about 200m north of the Forrestfield Station site. Dundas Road has been closed to traffic while work takes place to fix the leak and repair the road.

Both Herrenknecht Variable Density TBMs, which are more than 2km further on from this cross-passage, have been stopped while the repair work takes place.

No one was hurt in the incident. Safety managers are onsite and measures have been put in place to ensure worker safety.

Due to the leak there has been some movement of approximately 10 tunnel rings in the six piece segmental liningnear the point of the cross passage. Additional internal bracing is now in place as work continues to stop the leak and resolve the sinkhole damage.

TBM Grace is currently about 3km ahead of this cross passage site and TBM Sandy is located about 2.5km ahead of the site.

WA Transport Minister Rita Saffioti said,”The State Government is monitoring this very closely and working with Salini-Impregilo – NRW Joint Venture. We are hopeful a resolution can be found in the very near future.

“My number one priority is to ensure work is carried out safely.

“I have asked the Public Transport Authority to review the timeline of the project, to ensure worker safety is paramount.

“In addition, there will be a review into the method used to create future cross passages and surveys are now being undertaken of the ground and the two tunnels in the vicinity of this particular cross passage.”

The $1.86bn 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 via the 8km long twin tunnels.
In April 2016 the PTA awarded the $1.176bn single-package, lump sum design, construct and maintenance contract to Salini Impregilo – NRW Joint Venture.

TBM Grace began tunnelling in July 2017, with TBM Sandy following in September. Their underground journey is scheduled to take almost two years with breakthroughs slated for April 2019 and June 2019 respectively.

Earlier this month both tunnel boring machines (TBMs) reached another milestone, having now built a third of the entire length of the tunnels between Forrestfield and Bayswater Junction.

As a reward, TBM Grace has been equipped with a number of new cutterhead teeth and TBM Sandy will undergo the same treatment in the coming weeks.

With the machines now tunnelling between Airport Central and Redcliffe Stations, tunnel one has been closed between Forrestfield and the Airport to allow works to start on two new cross passages. All six multi-service vehicles are using the one tunnel, changing lanes at Airport Central Station to continue supplying segments to both TBMs.

To date, over 18,000 segments have been installed

A leak in one of the tunnels being dug for Perth’s Forrestfield-Airport link has caused the temporary cessation of work with the project’s tunnel boring machines.

The small leak occurred on Saturday during works aimed at creating a tunnel cross passage, a throughway to connect the two tunnels and which will be used as an emergency exit once the rail line is operational.

The incident reportedly occurred in tunnel one of the project around a cross passage adjacent to Dundas Road, 200 metres north of Forrestfield Station, which led to the formation of a sinkhole early on Sunday morning and closure of the road.

The tunnel boring machines have now stopped as a precautionary measure and work is continuing to stop ground water from leaking into tunnel one.

While that work is ongoing, a survey of the ground along Dundas Road and tunnel connecting to the cross passage is also underway.

Western Australian transport minister, Rita Saffioti, said that the state government was working with the Salini-Impregilo-NRW joint venture in finding a safe resolution to the situation.

“I have asked the Public Transport Authority to review the timeline of the project, to ensure worker safety is paramount,” Saffioti said.

“In addition, there will be a review into the method used to create future cross passages and surveys are now being undertaken of the ground and the two tunnels in the vicinity of this particular cross passage.”

Due to the leak there has been some movement of approximately 10 tunnel rings near the point of the cross passage. Additional internal bracing is now in place as work continues to stop the leak and resolve the sinkhole damage.

TBM Grace is currently about 3km ahead of this cross passage site and TBM Sandy is located about 2.5km ahead of the site.