Construction of larger diameter tunnels used to call for a new tunnel boring machine (TBM) for each project but a growing number are now being bored using refurbished machines in order to fast track projects.
According to US-based TBM manufacturer Robbins, customers now recognise that a rebuilt machine with updated systems can offer exceptional value without increasing risk.
“A rebuilt machine can usually be delivered faster,” said Robbins engineering manager Steve Smading. “While the financial and schedule advantages are obvious, the flexibility of used equipment may be less obvious. Boring diameters can be increased or decreased and machine configurations can even be changed.”
Robbins estimates that 50% of its Main Beam TBMs have now been used on three or more schemes.
One of the latest machines to achieve this has recently been used by Kenny Construction to complete driving of Chicago Department of Transportation’s Albany Park Stormwater Diversion Tunnel. Before working on the current scheme, the TBM bored tunnels in Dominican Republic, Saudi Arabia, New York and Chicago — totalling at least 19.5 km.
For the Albany Park Project, the TBM was rebuilt by Kenny Construction with size modifications designed by Robbins. Robbins took an existing cutterhead, repaired it, and then added segments, taking it from 5.2 m to 6.2 m in diameter. “Extensive modifications were also made underground to the machine to be able to install rock dowels and stand the ring steel under the roof shield,” said Kenny Construction project manager Clay Spellman.
The TBM broke through on the scheme last year and work is underway to fully open the diversion tunnel in spring this year.