Page 6 - TunnelTalk Annual Review 2011

Fig 1. Original (black) and revised (yellow) horizontal alignment Fig 2. Original (blue) and revised (green) vertical alignment
Mott MacDonald, OPG’s representative on the project, summed up the mood in those dark days. “Depressing! Absolutely depressing. The Robbins TBM was capable of doing a 1.4m to 1.8m push in about an hour and it was lucky if it accomplished that in a 24-hour cycle. It went on like that day after day for months and months.”
Things hit bottom that year when the strain and uncertainty threatened the project. Strabag’s original Can$600 million fixed price contract included a penalty of $Can250,000/day maximum for any delay beyond the contracted delivery date, and a bonus of 50% of that for every day earlier. With the original Fall 2009 completion schedule completely out of reach, tensions rose between the stakeholders and came to a head with a dispute resolution hearing.
A way forward
A resolution was reached at the end of 2008 to move the horizontal alignment further east to avoid the existing two tunnels, and also a vertical alignment change to move the TBM out of the Queenston Formation (Figs 1 and 2). The contract was also changed from a fixed price to a target price contract with the completion date pushed out to 2013 and a revised cost estimate of about Can$1.06 billion.
“I think reaching that agreement, to find a way forward and finish this project was a highlight,” said Tait. “Nobody liked it and everyone compromised. We had our disagreements and our arguments; said a few harsh words, but the day it was over, we shook hands, respected each other as professionals and got on with the job.”
Progress at last
Progress rates improved in the higher ground of the new alignment and 2009 saw the best advance rates of the entire project, including the Best shift: July 5, 14m (46ft); Best week: July 12, 153m (503ft); and Best month, July 468m (1,535ft). The Best day came on May 1 the following year (2010) with a record 25.4m (88.5ft) in 24 hours.
“Conditions were much better in the overlying rock formations compared to the Queenston Shale,” said Everdell. “Several kilometers of the tunnel have virtually no overbreak, so getting out of the Queenston Shale with the realignment was the right decision.”
Even so, average advance rates remained lower than expected in some sedimentary strata as overbreak continued
to dog the excavation, including a rockfall in September of 2009 when about 25m3 or 100 tonne fell from the two o’clock position in the crown some 2km (1.2 miles) behind the TBM, and about 3,600m (2.2 miles) into the drive.
The TBM
There were also plenty of small frustrations, including one that initially delayed delivery of the TBM, much of which was trucked from the Robbins plant in Ohio for an Onsite First Time Assembly (OFTA). A section of the massive cutterhead was waylaid at a Pennsylvania Turnpike weigh station for two weeks because it was more than the weight limit by 91kg (200lbs) and required a special permit, said Mike Kolenich, Project Manager for Robbins. “The thing is, when the load was re-weighed it was actually under the limit. Either the scale was off the first time, or our driver lost a heck of a lot of weight in the two-week layover!”
Despite the delay, the OFTA build was completed within the 12-month deadline and the massive 14.4m (47ft) diameter TBM performed as specified. “With all the challenges of the project, it is very satisfying to know the machine was not one of them,” said Kolenich. “Strabag also took great care of the TBM. It adopted a maintenance schedule and really stuck to it.”
The TBM, dressed with 20in discs, was modified slightly in the early stages of excavation due to the excessive overbreak. The work platforms behind the cutterhead were replaced with several man lifts to more easily manoeuver workers around the crown. Additionally, more protection was added to some of the vulnerable systems as a safeguard against the falling overbreak.
While the TBM’s work is done, there is still much to do, including the crown profile restoration work and completion of the concrete lining installation that has been underway since December 2008. By March 2011, the invert installation had progressed beyond 7km (4.3 miles) and the arch installation that began in May 2010, had progressed more than 2km (1.2 miles). Each concreting installation has two 12.5m long forms that cast in leapfrog sequence to complete 25m (82ft) a day.
At peak, the 24h/7d per week workforce totalled about 400.
Awe-inspiring
The sheer size of the TBM and magnitude of the operation never fails to impress even
the hardest cynic. “Everyone is awed by it,” said Everdell. “For the arch installation and membrane placement there is a train of work platforms that are about five stories in the air and about 450m (1500ft) long.”
“We are almost a tourist attraction,” said Tait. “Everyone wants to visit. I remember one colleague, who, according to him, has seen it all and done everything. I walked him into the tunnel early in the excavation right under the TBM and he looked up and said ‘Oh, holy moly!’ and that’s the best way I can describe it.”
For most involved, the Niagara is a career high. At 67, it comes near the end of Tait’s career. He should have retired two years ago, but is committed until the end of the project. “There were times, back in 2008, when we had the worst rock conditions and the schedule kept slipping that I questioned if the excavation could be finished, but we’re here, we made it, and give Strabag its due, they stuck it out, and kept at it, when another contractor might have walked away.”
Reflection
“In hindsight a target price contract with incentives and disincentives might have been a better way to start out the project, rather than a fixed price with incentives,” said Everdell. “OPG actually adopted that model on another project and would probably use it on other significant projects. You can get a better base price to begin with and it really does promote working together as a team that can respond quickly to challenges as they arise. I think it is a better fit for these major infrastructure projects.”
Tait and Everdell have little time for reflection with the project still two years from completion, but for the moment they are enjoying the successful completion of excavation. “There is a powerful sense of accomplishment,” said Tait, “so it is a great day for everyone involved.” n
References
• Positive progress for giant TBM at Niagara - TunnelTalk, June 2010
• Old bore hole causes rockfall in Niagara Tunnel - TunnelTalk, November 2009
• Accounting for slow progress at Niagara - TunnelTalk, July 2008
• Niagara plan of attack - TunnelTalk, December 2006
• Advocating for more DRBs in Canada - TunnelTalk, August 2010
• Modern large diameter rock tunnels - TunnelTalk, April 2010
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