The city released preliminary results of an investigation into the failure of the Bearspaw South feeder main late Friday afternoon, indicating there were a number of factors behind its failure.

The purpose of the investigation, which was overseen by Associated Engineering and Pure Technologies, was to better understand what led to the deterioration of the pipe until it failed on June 5, 2024.

Investigators isolated three possible factors in their Friday statement:

• Microcracking of the protective mortar outer layer of the pipe;
• High chloride levels in soil in various locations; and
• Wires that cracked due to corrosion and hydrogen embrittlement.

They concluded that there was no single factor that led to the failure of the feeder line in June.

“The Bearspaw South Feeder Main is an important piece of infrastructure, and it is responding well to the rehabilitation work that was completed between June and November and is now stabilized,” said Michael Thompson, Director of City of Calgary Infrastructure Services.

“Through our acoustic monitoring, we only recorded two wire snaps on the feeder line between October and November. In all of July and August there were 23 wire snaps.”

The preliminary examination of the construction of the tube and its operation confirmed that the original design conformed to the guidelines of the time.

The operation of the pipe was found to be well within the design parameters of the pipe.

What’s next

The final report will be presented to the city’s infrastructure and planning board on Dec. 11.

Construction of two other segments of the pipe, one along Parkdale Boulevard. NW between 26 Street and 27 Street NW and the other at the Memorial Drive exit onto Crowchild Trail northbound are both nearly complete.