Salini-Impregilo (SI-NRW) has suspended boring due to ‘ground disturbance issues’ on one of its two Herrenknecht Variable Density TBMs currently being used to construct the 8km long, 7m diameter Forrestfield-Airport Link twin tunnels in Perth, Australia. The decision was reportedly taken on February 14th, after discussions between SI-NRW, Perth Airport (PAPL), and the Public Transport Authority (PTA).
A spokesperson for the client said, “Due to some ground disturbance issues, tunnelling work by TBM Grace for the Forrestfield-Airport Link – which has not yet reached any critical airport infrastructure – has been temporarily suspended.
“The temporary suspension is a safe guard and will allow for the processes associated with the tunnelling to be independently reviewed and validated.”
The ‘ground disturbances’ occurred whilst the crews were tunnelling through the region’s Ascot Formation, which comprises complex non-cohesive granular material. Boring is being carried out at an average depth of some 15m, with a six piece segmental ring being erected for the tunnel lining.
The client has said that when the contract for the project was signed all parties involved were well informed about the potential challenges involved in tunnelling. Currently, PTA and PAPL have engaged separate independent tunnelling experts to review tunnelling operations and provide recommendations for improvement. SI-NRW is running detailed risk workshops to determine lessons that can be incorporated into tunnelling operations. A specialist advisor from Herrenknecht has also reviewed operations and provided recommendations for improvement.
“Tunnelling will recommence when PTA, PAPL and SI-NRW jointly agree to do so. Prior to this happening, an independent review is to be completed and any lessons need to be incorporated into tunnelling operations,” the spokesperson said. “At this stage there is no set timeframe for this to occur, however all parties are working together to progress the review in a timely manner. Tunnelling will not recommence until all parties deem it is appropriate to do so.”
TJ contacted SI-NRW but the JV was unable to comment.
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.
The representative for the client has been reported as saying that the hold-up should not affect the project opening date in 2020 due to the fact tunnelling was already ahead of schedule.