Breakthrough ends tortured journey at NiagaraMay 2011
Paula Wallis, TunnelTalk
The world's largest hard rock TBM received a hero's welcome today (March 13, 2011), following a long and tortured drive that tested the resolve of all involved. No shortage of dignitaries, media and invited guests were present to witness the massive TBM's breakthrough, marking the end of excavation on the 10.2km (6.3 mile) Niagara Tunnel for Ontario Power Generation (OPG).
On 1 March 2011, the TBM, named Big Becky, connected with a grout tunnel about 300m (984ft) from the intake structure and the end of its drive. Today's official breakout occurred with a final push of 1.3m (4ft 4in) for a total of 10,143m (33,277ft) excavated.
TBM's March connection with the grout tunnel
Severe overbreak led to alignment change
Ontario Premier Dalton McGuinty, OPG CEO Tom Mitchell, Strabag CEO Dr Hans Peter Haselsteiner, and Robbins CEO Lok Home were among those present at the celebration as well as hundreds of workers. Guests also included Rick Everdell who began his career with OPG's predecessor, Ontario Hydro, right out of college on the project. He began on the feasibility studies to expand capacity at the hydroelectric complex in 1982 and has remained with the project almost 30 years through its various incarnations, and rising to the position of Project Director for the client.
Tunnel by the numbers Tunnel - 10.2km long (6.3 miles) TBM - 14.4m diameter TBM (47.2ft) Excavated material -1.7 million m3 (5.6 million ft3) Concrete for liner - 400,000m3 (1.3 million ft3) Tunnel capacity - 500m3 (1,640ft3) of water per second Power generation - 1.6 billion kilowatt hours annually
Who's who Stakeholders
Ontario Power Generation (OPG) - Client
Hatch Mott MacDonald (USA) - Construction Management
Strabag (Austria) - Contractor Associated Companies
ILF (Austria) and Morrison Hershfield (Canada) - Tunnel Designers
Robbins (USA) - TBM supplier
"It is terrific for a civil engineer like me, having started out on such an ambitious project, to see the excavation come to a successful end," said Everdell. “The project has certainly had its share of setbacks, including an economic downturn and reorganization of the power industry in the late 1990s that forced the cancellation of an earlier tender process and reduced the project from its original two tunnels plus a new powerhouse, to the single tunnel. Then there were challenging ground conditions once we got into excavation. Still, after four and a half years of tunneling, the TBM is finally at the finish line."
Strabag won the design-build contract in August 2005. Having successfully completed the previous largest ever hard rock TBM tunnel on the Manapouri Hydroscheme in New Zealand about six years earlier, the Austrian contractor was uniquely experienced. Strabag’s Project Manager in New Zealand, Ernst Gschnitzer, would also take the reins at Niagara. But almost from the get-go the excavation was hijacked by extensive overbreak, requiring the removal of large amounts of material that slowed advance rates to a crawl.
"The most challenging days were in 2007 when the TBM entered into the Queenston Formation before the St. David Gorge and at a maximum depth of 140m (459ft)," said Everdell. "Significant overbreak meter after meter, essentially blew out the schedule."
John Tait, Project Manager for Hatch 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 Strabag 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 uncertainly 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 exiting two tunnels and change the vertical alignment to move the TBM out of the Queenston Formation (Fig 1-4). The contract was also changed from a fixed, to a target price contract with the completion date pushed out to 2013 and a revised cost estimate of about Can$1.06 billion.
Fig 1. Original horizontal alignment
Fig 2. Revised horizontal alignment
"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, and 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, where about 25m3 or 100 tons 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.
Fig 3. Original vertical alignment
Fig 4. Revised vertical alignment
There were also plenty of small, frustrations too, including one that initially delayed delivery of the TBM, much of which was trucked from Robbins' plant in Ohio for an on on-site assembly. A section of the massive cutterhead was waylaid at a Pennsylvania Turnpike weigh station for two weeks because it was over 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 onsite 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 in 20-inch cutterheads, 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 maneuver 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. The invert installation has progressed beyond 7km (4.3 miles) and the arch installation that began in May 2010, has 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. A peak workforce of about 400, working in three, 24h/7d shifts are assigned to the several concurrent operations.
The shear magnitude of the operation and the size of the TBM and its trailing gear never fail 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 long (1500ft)."
"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 s—t!' 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."
"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 everyone involved."
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