The City of Calgary has released the findings of an investigation into the June 5 catastrophic failure of the Bearspaw South Feeder Main, identifying a combination of factors that led to the water pipe rupture. The investigation was led by Associated Engineering and included in-depth analysis of the damaged pipe and surrounding conditions.Key findings indicate that the break resulted from a loss of structural integrity due to extensive damage to the pipe’s prestress wires — critical components wrapped under tension around the pipe’s concrete core. The wires were found to have suffered from microcracking, chloride-induced corrosion, hydrogen embrittlement, and stress corrosion cracking. Microcracks in the pipe’s outer mortar layer allowed 'aggressive soils' and chlorides to penetrate, leading to wire pitting and brittleness.Steve Wyton, Manager of Asset Management Planning, emphasized the importance of the findings in shaping future measures. “Our priority now is planning for the long-term rehabilitation of the feeder main and implementing proactive measures to ensure a reliable and resilient water distribution system for Calgarians,” said Wyton. He highlighted the city’s commitment to adopting advanced monitoring technologies, contingency planning, and strategic investments.The report ruled out several potential contributors to the failure, including:Manufacturing defects from 1975 standards.Corrosion from stray electrical currents.Operational pressures from the Bearspaw Water Treatment Plant.Transient pressure events or live loading after construction.Further investigations are planned to address elevated chloride levels found in the soil, which are suspected to have exacerbated the damage.The city plans to provide interim updates in early 2025, focusing on enhancing system redundancy and improving north and south water servicing. By mid-2025, an implementation plan for rehabilitating the feeder main is expected.
