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Concrete Collapse Traps 3 in Tunnel

Monday, November 14, 2016

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Canadian safety officials are investigating an accident in a light rail transit project tunnel that temporarily trapped three construction workers Thursday (Nov. 10).

Two of the three were uninjured in the incident, and the third reportedly sustained a “non-specified hand injury,” according to the National Post.

Although initial reports indicated the tunnel had collapsed, numerous sources later confirmed that only a section of shotcrete and rebar had fallen into the area where the men were working and the tunnel itself did not collapse.

The City of Ottawa, where the accident occurred, simply attributed the cause of the collapse as “related to construction,” in a post to Twitter.

Shotcrete Application in Progress

The men were at work on Ottawa’s $2.1 billion Confederation Line light rail project, for which Rideau Transit Group (RTG) serves as contractor.

The tunnel is constructed of horizontal steel supports reinforced with a layer of sprayed shotcrete, which is to be applied to the full 2.5-kilometer (about 1.6-mile) length of the tunnel.

The workers were reportedly in the process of applying the material along a tunnel wall when pieces of rebar came loose and a section of the sprayed concrete fell on their equipment shortly before 4:30 p.m., the Toronto Star reported.

Shotcrete operations
Photos: City of Ottawa

Shotcrete operations are underway in various parts of the downtown tunnel for Ottawa's new Confederation line.

The workers were said to be sheltered in a “safe zone” when emergency crews arrived, but those on site soon concluded that it was not a rescue operation, the workers were safe, and the tunnel as a whole remained stable.

By 5:20, fire officials had walked the men from the tunnel, where paramedics evaluated them and sent one to the hospital with minor injuries.

“It was not a tunnel collapse at all. It was one small portion of rebar and the sprayed concrete that fell,” Ottawa Mayor Jim Watson said.

Watson indicated he was told that approximately six kilograms (about 13 pounds) worth of material fell.

It is believed that some of the buckled steel coming into contact with the workers’ equipment caused the hand injury.

“We were very fortunate that no one was seriously injured,” he added.

The surface street suffered no damage in the incident, and work went on without interruption in other areas of the project nearby.

Peter Lauch, technical director for RTG, indicated that the workers were using safe operating procedures.

Third Tunnel Incident

Although RTG classified the event as minor, according to the Ottawa Citizen, it is under investigation by inspectors from the Ministry of Labour, the province’s agency responsible for labor issues including occupational health and safety.

The construction area will remain closed as a result of the investigation.

No work will take place in this portion of the tunnel until the ministry gives the all-clear sign,” Watson said.

It is reportedly the third emergency incident on the LRT project in two years.

Having occurred near the intersection of Waller Street and Laurier Avenue close to the University of Ottawa campus, the incident is in the vicinity of where a section of the surface of Waller Street caved in during tunneling operations in 2014.

rockbolting and shotcreting

The workers were said to be sheltered in a “safe zone” when emergency crews arrived, but those on site soon concluded that it was not a rescue operation, the workers were safe, and the tunnel as a whole remained stable.

That collapse was attributed to “unanticipated soil conditions” at the site, and engineers indicated that the tunnel crossed a “previously excavated construction pit” that had been missed in site examinations.

Additionally, this June, a sinkhole had opened up just a few blocks away where tunneling was in progress, although the mayor noted that the cause of that incident has not yet been determined.

Risk and Safety

Watson noted that anyone working in tunnel projects is aware of the ever-present risks. However, he added, “We have some of the best tunnel engineering working on this project and safety is our first and foremost concern for the employees.”

Although it’s not clear whether the three workers were members of the Labourers’ International Union of North America Local 527, a union representative was reportedly on site following the accident to talk with workers.

“Obviously the safety of our workers is always a concern, even if there was no incident,” LiUNA Business Manager Luigi Carrozzi said. “It’s definitely one of the concerns when you’re tunnelling, cave-ins occasionally do happen, so we need to speak to members to find out exactly what happened.”

Confederation Line

The Confederation Line LRT system is said to be Ottawa’s largest transportation infrastructure project since the construction of the 126-mile Rideau Canal built in 1832.

The 12.5-kilometer (about-7.8 mile) line includes a 2.5-kilometer tunnel through the downtown core, 13 stations, a maintenance and storage facility and the purchase of 34 Alstom CITADIS Light Rail Vehicles.

The downtown portion of the project is expected to be largely completed in 2017, in recognition of the 150th anniversary of Canada's Confederation, and is slated to be open in 2018.


Tagged categories: Accidents; concrete; Health & Safety; Health and safety; Infrastructure; Mass transit; North America; Public Transit; Rebar; Steel; Transportation; Tunnel

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