When tunnel boring machines hit a problem, the challenge is notoriously a difficult one. On the Eurasia Tunnel project in Istanbul, for the first time, manufacturer Herrenknecht had to come up with a maintenance solution that could work in extremely deep conditions.
“This was a machine designed for this project and for the first time had working chambers, which can let you change the cutters and some tools of the machine in zero pressure,” says JV project manager Naim İşli.
The up to 11 bar pressure encountered 106m below sea level had to be anticipated and proved challenging for even the most established TBM designer out there.
“Herrenknecht was challenged by the design also,” says İşli, who adds that as a result, the project became high profile for all involved and resulted in the firm’s owner, Martin Herrenknecht, visiting the site six or seven times.
If this project has a problem like the one in America, then you can forget about the big TBMs for a while because nobody will insure them.
“It gives an indication how important it was for them also,” İşli points out. “And they have bigger sized machines in Hong Kong and the States but I believe he never visited those because the ground formation, condition and pressures was unique.”
Nervousness about high profile TBM problems – such as those that hit a Hitachi Zosen machine on the Alaskan highway in Seattle – added pressure to this scheme. “Martin Herrenknecht was telling me, if this project has a problem like the one in America, then you can forget about the big TBMs for a while because nobody will insure them,” says contractor Yapı Merkezi board member Başar Arıoğlu.
Inevitably, the special maintenance regime put in place was tested – about halfway through the project, at one of the deepest points in tunnelling.
Eurasia Tunnel geology and tunnelling machine
Professionally trained saturation divers capable of steel work spent three weeks working in conditions not far off what faces those working on the International Space Station.
The parts needing repair were located in the working chamber, behind the cutter head; an area under pressure.
In eight hour shifts the specialist team worked at the heart of the machine, remaining in special chambers outside the tunnel – also under pressure. Given the days it takes in a hyberbaric chamber to allow their bodies to adjust very slowly to the appropriate working pressure, it was not feasible to bring them into the normal atmosphere during works. Internet access became almost their sole and best entertainment.
The team carried out four significant hyperbaric maintenance events over the project – dealing with pressure ranges from 9.8 bar to 10.8 bar (see graph).
“Whatever they have to do, they have to do inside the chamber,” says Arıoğlu. “Everything is special, it’s like being in a space mission – it’s the same idea.”
Graph showing the hyperbaric maintenance events on the scheme
How to fix a tunnel boring machine under extreme pressure