A sinkhole eight metres wide and 12 metres deep opened up at the construction site where crews are digging the eastern entrance to Ottawa's light rail tunnel, and officials are trying to determine why.

Ottawa Sinkhole 20140221

Crews work on a large sinkhole that halted tunneling work on the East Portal of Ottawa's LRT project. (Fred Chartrand/Canadian Press)

No one was injured. It happened on Waller Street, just south of Laurier Avenue, and tunnelling operations at the site have stopped.

A digging crew in the tunnel first noticed dirt falling into the tunnel at about 10 p.m. ET Thursday, where the excavator — a roadheader called Crocodile Rouge — was gouging the earth, said deputy city manager Nancy Schepers during a technical briefing on Friday.

"As they continued to observe material entering the tunnel, and the rates increased, the crew suspended tunnelling operations and immediately notified [Rideau Transit Group's] management to discuss next steps and a stabilization strategy. City staff were also notified at that time," Schepers said.

By 1 a.m., a large sinkhole had opened up on Waller Street.

"We can only confirm that it was directly above where tunnel excavation was occurring, and at this point we cannot confirm its root cause," Schepers said.

Soil conditions in area of collapse 'challenging'

Waller Street sinkhole (Feb. 21, 2014)

This sinkhole formed early Friday after a road collapse in downtown Ottawa. (Photos courtesy of John Holtby and Brian Bancroft)

RTG crews had begun 24-hour tunnelling operations on Wednesday. Schepers said the city and crews were aware that soil conditions were different in the area.

"We were aware of different geotechnical conditions in this vicinity, and some of you will recall that before we went out to tender we actually shortened the length of the tunnel, recognizing that this type of material would be challenging. Certainly we provided all that geotechnical data," Schepers said.

"Monitoring equipment has confirmed that the impact is localized, and the geotechnical team has not identified any safety concerns at this point."

The Crocodile Rouge roadheader is about 20 metres away from solid bedrock that two other excavators are working on, in different sections of tunnel, elsewhere in Ottawa.

Investigation under way

Ottawa sinkhole graphic tunnel

This graphic shows the sinkhole happened next to where a tunnel-digging machine was working earlier this month. (CBC)

"I would like to assure you that public safety is a priority for both … the city and RTG, and I can assure you that all steps are being taken to first protect the public and all physical assets in the immediate area. I can also assure you that tunnelling will not resume until both ourselves and RTG are comfortable that it is safe to do so," Schepers said. 

"I think we are very fortunate there were no injuries associated with the incident … and all efforts are being made to, number one, secure the site to do a thorough investigation, and then finally put in a plan to begin resuming our tunnelling operation."

LRT east portal (Feb. 21, 2014)

This photo courtesy of the City of Ottawa shows the work ongoing underground for the LRT east portal. (Photo courtesy of City of Ottawa)

RTG crews are using concrete to reinforce the area. 

Water, sanitary and storm services to 50 Laurier Ave. are affected. Traffic lights at the intersection of Laurier Avenue and the Transitway are not working and police are directing traffic, said Kevin Wylie, the city's manager of roads and traffic operations.

Traffic and buses are being rerouted, and one lane of Laurier Avenue eastbound is closed between Queen Elizabeth Drive and Waller to allow for a cement truck staging area.

Corrections

  • An earlier version of this story attributed comments made during a technical briefing to Lecia Stewart of the Rideau Transit Group. In fact, it was RTG's construction director, Tim Stewart, who spoke at the briefing.
    Feb 21, 2014 3:11 PM ET