Rideau Street sinkhole likely caused by soil collapse, not watermain: report

The long awaited report on the Rideau Street sinkhole has finally been released.

The engineering report backs up what the City has been saying about the Rideau Street sinkhole, that it was likely caused by LRT tunneling and sandy soil and not by the City's infrastructure.

The report, released Wednesday afternoon, says sandy, saturated soil collapsed, breaking the water pipe, and causing the large crater to open up.

"The loss of ground likely occurred very rapidly because the ground had previously been disturbed and loosened in response to pipe umbrella installation and the West Rideau Station Entrance excavation," the report says. "This loss of ground then likely resulted in loss of support for the 305 mm watermain on the south side of Rideau Street and its subsequent catastrophic rupture. Water flowing from this rupture then caused erosion of the loosened, sandy soils below the watermain and the flow of a vast amount of soil into the west running tunnel, thereby creating the large sinkhole."

The report further states “forensic examination provides no evidence that the 300 mm PVC watermain is linked to the root cause of the sinkhole.”

If it were the other way around, taxpayers and the City would have been on the hook.

The report by external experts was previously kept private. It was released Wednesday after access to information requests.

The sinkhole opened June 8, 2016 and took weeks to repair. Businesses affected by the sinkhole have made 32 claims for compensation resulting from the event, which have been referred to the project's insurer. The City claimed $1.5 million in costs arising from the sinkhole.

In a memo to councilors sent Wednesday afternoon, City Solicitor Rick O’Connor says the City submitted a second insurance claim for $780,000 on March 24, 2017, to cover secondary costs incurred by the sinkhole, including legal fees, City staff costs, and the preparation of the above-mentioned report.