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A root cause report makes it clear that LRT tunnelling work in soft ground likely contributed to the massive sinkhole forming on Rideau Street last June.
Wet, sandy conditions and groundwater pressure above the top of the tunnel pushed soil down on June 8, 2016, after workers below constructed a reinforcing “pipe umbrella” support system, which had disturbed the soil, the report says. A watermain broke as the supportive soil washed away.
Photos: A look back at the Ottawa sinkhole
The city released the report Wednesday after receiving access to information requests, including those from the Postmedia, for the document earlier this year.
The city hired McMillen Jacobs Associates for the sinkhole investigation.
Around 10:30 a.m. on June 8, 2016, a massive crater opened up on Rideau Street, just east of Sussex Drive, and an exposed underground pipe was spewing water into the sinkhole. A minivan fell into the hole and it’s now encased in concrete under the road.
Steve Cripps, director of the O-Train project, said it was a unique situation, but the soft ground conditions in that area were intimately known by Rideau Transit Group’s tunnelling experts.
“This was no surprise,” Cripps said in an interview. “There was a lot of geotechnical investigation in that area. Everyone knew this. RTG knew this. They took appropriate precautions. (RTG has) world-class tunnelling experts as part of that team. They took appropriate steps, but there are risks with tunnelling and these things happen.”
Cripps noted the report didn’t come to any one reason why the sinkhole happened.
The report says there was evidence of ground movement on the surface of Rideau Street in the days before the sinkhole. A photograph dated June 6, 2016, illustrated a separation between the sidewalk and a curb.
Cripps said tunnelling normally causes ground movements, which are monitored constantly by several devices, so evidence of the shifting wouldn’t be a surprise.
“The ground is moving when they tunnel and that’s just a natural occurrence,” according to Cripps.
It’s obvious the watermain didn’t break before the sinkhole happened since the Rideau station west entrance excavation would have had water pouring into it if there was a pipe break, Cripps said.
Indeed, an expert’s close examination of the 305-millimetre pipe, which ran on the south side of Rideau Street, concluded an “external force” from above the pipe caused the failure, not an overpressurizaiton. A second expert saw no evidence in photographs of a pre-existing leak or crack that caused the break.
The report notes the RTG’s “sequential excavation method” of tunelling is generally less risky moving from soil to bedrock, but at some point a decision was made to also tunnel from west to east, that is, from bedrock into the soil.
The collapse started between 10:15 a.m. and 10:30 a.m. Workers in the tunnel started noticing high water flows and ground instability at the tunnel face and they evacuated.
There were no injuries reported.
The sinkhole in the heart of Canada’s capital received international attention.
It wasn’t until Dec. 15 that Rideau Street opened to buses and pedestrians.
Until now, no one has drawn a line between the sinkhole and tunnel work.
When the root cause report was finished in December, the city decided against releasing the document to the public because of the legal claims related to the sinkhole.
The city assured council, though, that it wasn’t at fault for the sinkhole.
Thirty-two businesses filed claims for compensation as of Wednesday. The city claimed $1.4 million for emergency remediation work, plus another $780,000 recently for other costs, such as legal and consultant fees.
It was all sent to the LRT project’s insurance company to sort out.
The insurer hadn’t made a decision on the claims as of Monday, the city said.
The $2.1-billion Confederation Line LRT between Tunney’s Pasture and Blair station is scheduled to open in 2018. RTG has told the city the project remains on track to open next year.
The 2.5-km tunnel is now completely excavated and either has a permanent liner or temporary liner as workers continue to build it.
“The tunnel is perfectly safe and perfectly reinforced,” Cripps said.
Cripps lauded RTG for a quick response to the sinkhole to make sure everything around the crater was safe.
“I think that RTG got in there with 3,000 cubic metres of concrete fast stabilized buildings and stabilized soil,” Cripps said. “They should be commended for their response, actually. They did a really good job.”
jwilling@postmedia.com
twitter.com/JonathanWilling
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Wet, sandy conditions and groundwater pressure above the top of the tunnel pushed soil down on June 8, 2016, after workers below constructed a reinforcing “pipe umbrella” support system, which had disturbed the soil, the report says. A watermain broke as the supportive soil washed away.
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Photos: A look back at the Ottawa sinkhole
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Photos: A look back at the Ottawa sinkhole
Day 1: View from Chateau Laurier. Sink hole on Rideau St and gas leak in Ottawa, June 08, 2016. Jean Levac/Ottawa Citizen
Day 1: Sink hole on Rideau St and gas leak in Ottawa, June 08, 2016. Jean Levac
Day 1: View from Chateau Laurier. Sink hole on Rideau St and gas leak in Ottawa, June 08, 2016. Jean Levac/Ottawa Citizen
Day 2: Rideau street sinkhole on Thursday morning. Tom Spears/Ottawa Citizen
Day 2: sinkhole on Rideau Street Thursday June 9, 2016. Ashley Fraser/Ottawa Citizen
Day 2: sinkhole on Rideau Street Thursday June 9, 2016. Ashley Fraser/Ottawa Citizen
Day 3: View of the sinkhole from the Rideau Centre, June 10, 2016 Jean Levac/Ottawa Citizen
A photo of the Rideau Street sinkhole taken four days after the ground disappeared. /Ottawa Citizen
Day 5: Construction crews were at work Sunday June 12, 2016 as pedestrians and shoppers got a peek of the status of the sinkhole from the pedestrian bridge. Ashley Fraser/Postmedia
Day 6: The sinkhole on Rideau St., near Sussex Ave corner in downtown Ottawa Monday. Julie Oliver/Ottawa Citizen
Day 6: The sinkhole on Rideau St., near Sussex Ave corner in downtown Ottawa Monday. Julie Oliver/Ottawa Citizen
Day 7: Repair work continues on the sinkhole at Rideau near Sussex in downtown Ottawa. Julie Oliver/Ottawa Citizen
Day 8: Ottawa sinkhole from Rideau Centre, June 15, 2016. Jean Levac/Ottawa Citizen
Day 9: Sinkhole on Rideau June 16, 2016. Julie Oliver/Ottawa Citizen
Day 10: Ottawa Sinkhole Wayne Cuddington
Day 11: Daily progress photo of the Rideau Street sinkhole Saturday June 18, 2016. Ashley Fraser/Postmedia
Day 12: Repairs on the Ottawa Sinkhole on Rideau St. continue Sunday June 19, 2016. Darren Brown
Day 13: Ongoing construction work to repair the massive sinkhole on Rideau Street in downtown Ottawa. Monday June 20, 2016. Errol McGihon/Postmedia
Day 14: Repairs to the Ottawa sinkhole continues on Rideau St. Tuesday June 21, 2016. Darren Brown/Ottawa Citizen
Day 15: Sinkhole on Rideau Street in Ottawa June 22, 2016. Jean Levac/Ottawa Citizen
Day 16: Sinkhole on Rideau St. in Ottawa, June 23, 2016. Jean Levac/Ottawa Citizen
Day 17: Sinkhole on Rideau St. in Ottawa, June 24, 2016. Jean Levac/Ottawa Citizen
Day 18: Sinkhole on Rideau Street Saturday June 25, 2016. Ashley Fraser/Postmedia
Day 19: The sinkhole on Rideau Street, near Sussex, in downtown Ottawa June 26, 2016. Julie Oliver/Ottawa Citizen
Day 20: Ongoing construction at the scene of a sinkhole at Rideau Street and Sussex Drive in Ottawa. Monday June 27, 2016. Errol McGihon/Postmedia
Day 21: Sinkhole at Rideau St and Sussex Dr. Wayne Cuddington
Day 22: The Rideau St sinkhole as the downtown core deals with a number street closures for the Three Amigos Summit being held at the National Gallery. Wayne Cuddington
Day 23: Work on the Rideau St. sinkhole continues Thursday June 30, 2016. Darren Brown/Ottawa Citizen
Day 24: Canada Day revellers make their way up and down Rideau Street where the sinkhole was downtown Ottawa Friday July 1, 2016. Ashley Fraser/Postmedia
The city released the report Wednesday after receiving access to information requests, including those from the Postmedia, for the document earlier this year.
The city hired McMillen Jacobs Associates for the sinkhole investigation.
Around 10:30 a.m. on June 8, 2016, a massive crater opened up on Rideau Street, just east of Sussex Drive, and an exposed underground pipe was spewing water into the sinkhole. A minivan fell into the hole and it’s now encased in concrete under the road.
Steve Cripps, director of the O-Train project, said it was a unique situation, but the soft ground conditions in that area were intimately known by Rideau Transit Group’s tunnelling experts.
“This was no surprise,” Cripps said in an interview. “There was a lot of geotechnical investigation in that area. Everyone knew this. RTG knew this. They took appropriate precautions. (RTG has) world-class tunnelling experts as part of that team. They took appropriate steps, but there are risks with tunnelling and these things happen.”
Cripps noted the report didn’t come to any one reason why the sinkhole happened.
The report says there was evidence of ground movement on the surface of Rideau Street in the days before the sinkhole. A photograph dated June 6, 2016, illustrated a separation between the sidewalk and a curb.
Cripps said tunnelling normally causes ground movements, which are monitored constantly by several devices, so evidence of the shifting wouldn’t be a surprise.
“The ground is moving when they tunnel and that’s just a natural occurrence,” according to Cripps.
It’s obvious the watermain didn’t break before the sinkhole happened since the Rideau station west entrance excavation would have had water pouring into it if there was a pipe break, Cripps said.
Indeed, an expert’s close examination of the 305-millimetre pipe, which ran on the south side of Rideau Street, concluded an “external force” from above the pipe caused the failure, not an overpressurizaiton. A second expert saw no evidence in photographs of a pre-existing leak or crack that caused the break.
The report notes the RTG’s “sequential excavation method” of tunelling is generally less risky moving from soil to bedrock, but at some point a decision was made to also tunnel from west to east, that is, from bedrock into the soil.
The collapse started between 10:15 a.m. and 10:30 a.m. Workers in the tunnel started noticing high water flows and ground instability at the tunnel face and they evacuated.
There were no injuries reported.
The sinkhole in the heart of Canada’s capital received international attention.
It wasn’t until Dec. 15 that Rideau Street opened to buses and pedestrians.
Until now, no one has drawn a line between the sinkhole and tunnel work.
When the root cause report was finished in December, the city decided against releasing the document to the public because of the legal claims related to the sinkhole.
The city assured council, though, that it wasn’t at fault for the sinkhole.
Thirty-two businesses filed claims for compensation as of Wednesday. The city claimed $1.4 million for emergency remediation work, plus another $780,000 recently for other costs, such as legal and consultant fees.
It was all sent to the LRT project’s insurance company to sort out.
The insurer hadn’t made a decision on the claims as of Monday, the city said.
The $2.1-billion Confederation Line LRT between Tunney’s Pasture and Blair station is scheduled to open in 2018. RTG has told the city the project remains on track to open next year.
The 2.5-km tunnel is now completely excavated and either has a permanent liner or temporary liner as workers continue to build it.
“The tunnel is perfectly safe and perfectly reinforced,” Cripps said.
Cripps lauded RTG for a quick response to the sinkhole to make sure everything around the crater was safe.
“I think that RTG got in there with 3,000 cubic metres of concrete fast stabilized buildings and stabilized soil,” Cripps said. “They should be commended for their response, actually. They did a really good job.”
jwilling@postmedia.com
twitter.com/JonathanWilling
查看原文...
