Rideau sinkhole caused by Ottawa’s sandy soil, not pipe break: City report

by Michael Mosher on April 20, 2017

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The city has released its report on the cause of the June 8 Rideau Street sinkhole, which blames the incident on sandy soil conditions rather than a faulty watermain.

“It is highly likely that the root cause of the sinkhole was instability of the saturated sandy soil,” reads the report, compiled by engineering consultants McMillen Jacobs Associates on behalf of the city.

The report was kept confidential for three months but released Wednesday.

City Clerk Rick O’Connor said the city has received 32 insurance claims from businesses and property owners affected by the sinkhole. Those have been passed on to the city’s insurance provider, along with a claim for $1.4-million in costs associated with emergency personnel.

A second $780,000 claim was filed on March 24 for “secondary costs” including consultant fees, city staff costs, legal costs and the root cause report.

The 27-page document includes detailed technical information provided by the Ottawa Light Rail Transit Constructors, including soil analysis and a timeline of events on the days leading up to the sinkhole.

It notes that the ground along Rideau Street east of Sussex Drive is made up of soft, sandy soil as opposed to bedrock.

According to the report, when the disturbed sandy soil began to flow, it led to the erosion of soil around the large city watermain. The sudden change resulted in the pipe burst, which quickly eroded even more soil and resulted in the massive sinkhole.

The most important part of the report is that it is “highly unlikely based on the available information” that the city-operated pipe burst on its own. If the pipe had been the original source of the sinkhole groundwater levels and flooding would have been obvious in the days leading up to the sinkhole, according to the report.

That information is crucial to the city’s insurance claim, which includes the cost of emergency response staff.

“As of April 3, 2017, the insurer has not made a determination concerning the claim,” said O’Connor in a memo to council.

 

 

Read the full story here

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