It’s too soon to say whether construction on a tunnel and station for Ottawa’s new light rail system contributed to the enormous sinkhole that opened in the city’s downtown Wednesday morning, according to the mayor.
“At this stage we can’t confirm that,” said Ottawa mayor Jim Watson at a press conference Wednesday afternoon.
“So we can’t confirm whether the tunnel had any impact on the sinkhole, or whether it was a water main break or whether it was a leak of some type that destabilized the soil. We hope to have that answer obviously in the next few days.”
READ MORE: Huge sinkhole opens in downtown Ottawa
Ottawa’s new LRT, slated to open in 2018, runs underneath the downtown core for 2.5 kilometres. The new “Rideau Station” will be located just a few metres east of where the sinkhole opened at Rideau and Sussex streets. A tunnel runs directly under Rideau Street, and right under the sinkhole – though Watson says that the tunnel is located “substantially below” where the water main break took place.
Workers were in the tunnel, finishing the last few metres of excavation, when the hole appeared. They were immediately evacuated as a precaution, he said. The tunnel hasn’t been affected, but work has been suspended while they assess the situation.
The hole widened at one point during the morning to stretch across three lanes of the road – tipping a van into its depths. The van’s owner was a lucky man though. According to Kim Ayotte, the deputy chief of Ottawa Fire Services, the owner asked fire crews in the area if he could move it, when he saw that it was sitting on the edge of the hole. He was not permitted to do so, and moments later the van fell in.
The nearby Rideau Centre shopping mall and other nearby buildings were evacuated because of a broken gas line and fears of soil stability in the area. Although the gas line has since been cut off, engineers will assess the stability of the site before allowing people back in.
Sandy soil
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The soil in the area is sandy and gravelly, according to Steve Cripps, director of Ottawa’s rail implementation office, and as such the construction company digging the tunnel has been taking “extensive precautions” to deal with it. “Their whole mining technique, compared to the balance of the tunnel is different. The equipment they use, the way they reinforce it is different.”
The massive tunnel-boring machines used to excavate much of the tunnel weren’t being used there because of the soil conditions, he said, and buildings in the area have monitoring equipment to detect any sudden earth movement.
No other construction, aside from some renovations at the sinkhole-adjacent Rideau Centre mall and digging a station entrance down the road, were happening Wednesday morning.
Not the first hole
This isn’t the first time that Ottawa’s had a sinkhole near LRT construction. In February 2014, a sinkhole measuring roughly three metres by three metres appeared near the intersection of Laurier Avenue and Waller Street.
At that time, a tunnel-boring machine called a road header was working under Waller Street. However, according to a report in the Ottawa Citizen, excavators encountered a pit dug during a past construction project — filled with poor quality, uncompacted material. Workers noticed loose, wet material starting to fall and closed the area to traffic before it reached the surface and the road fell in.
Anthony Di Monte, general manager of emergency and protective services for the city, said that engineers are using a variety of technologies, including drones, to assess the damage, find out the cause of the sinkhole, and how to fix it.
City officials couldn’t estimate on Wednesday afternoon how long it might take for the hole to be fixed. Watson urged residents to check the city website, Ottawa.ca, for updates.
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