After more than seven years of construction the outlet gate at the challenging Niagara Tunnel Project in Ontario, Canada, is open.
In the presence of representatives from the client, Ontario Power Generation (OPG), design consultants Hatch Mott McDonald/Hatch Acres, and Austrian construction group Strabag, water was allowed to flow through the 10.1km water supply tunnel near the famous waterfalls on the Niagara River on March 21 (2013).
Fig 1. Original horizontal alignment
Fig 2. Revised horizontal alignment
"Thanks to the years of commitment by the Strabag team the project could be concluded as both a technical and financial success months before the contract deadline," said Strabag CEO Hans Peter Haselsteiner.
Breakthrough on March 21, 2011
The construction contract was awarded to Strabag as a Can$600 million Design-Build fixed price contract in 2005, and tunnelling works commenced in September the following year. But after just a short distance into the drive extremely difficult geological conditions prevented standard tunnelling with the largest hard rock TBM in the world. Special technical measures, alterations to the TBM and innovative solutions had to be found to continue work on the 14.5m o.d. tunnel.
Following a successful dispute resolution process a revised contract and schedule was negotiated in 2009, and in the event project completion was delivered Can$100 million lower than the revised Can$1.6 billion and nine months earlier than projected.
"Congratulations to our contractor Strabag and the hundreds of men and women who worked with extremely difficult rock conditions to safely complete this engineering marvel," said Tom Mitchell, OPG President and CEO. "The completion of this project will provide Ontario with a source of clean energy for the next 100 years."
Table 1. Progress record for Niagara Tunnel Project
Project initiated. Original project cost estimated at Can$ 985 million with a scheduled completion of June 2010.
Tunnel project awarded to Strabag of Austria for a fixed price of Can$600 million, with a penalty of Can$250,000/day beyond the Fall 2009 completion schedule. Contractor is selected for its unique experience, having the previous year successfully completed the previous largest ever hard rock TBM tunnel on the Manapouri Hydroscheme in New Zealand.
Excavation begins with a world record 14.4m Robbins main beam gripper TBM.
TBM enters Queenston Formation, and at 140m depth the TBM encounters significant and repeated overbreak. Progress slows to a rate of 1.4m-1.8m/day for months on end.
Following a successful dispute resolution hearing it is agreed to move the horizontal alignment further east to avoid the existing two tunnels and change the vertical alignment upwards by 45m to move the TBM out of the Queenston Formation (Figs 1 and 2). Contract changed from a fixed to a target priced contract with completion put out to the end of 2013 and a revised estimate of Can$1.06 billion.
Progress rates along the new alignment improve considerably and in July 468m is excavated. But average rates are lower than anticipated and in September 25m3 (100 tonne) of rock falls in the crown some 2km behind the TBM and 3.6km into the drive.
By June the TBM has reached 6.8km of its 10.1km drive
March 13, 2011
After five years breakthrough is achieved.
March 21, 2013
Outlet gates open, as project comes in Can$100 million under the revised budget, and nine months ahead of the revised schedule.
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