Rehabilitating Moose Jaw’s Thunderbird Viaduct will restore high priority heritage bridge

The City of Moose Jaw, Saskatchewan undertakes a comprehensive bridge asset management program, which encompasses inspections, assessments, and repair and rehabilitation of its bridge inventory. The Thunderbird (4th Avenue) Viaduct, which connects the South Hill community to downtown Moose Jaw, serves as a vital link in the City.

The Thunderbird Viaduct was constructed in 1929, replacing a wooden structure built in 1910, The structure spans Thunder Creek, the CP Rail Yards, and a CN spur line. The 417-metre-long viaduct includes 42 spans comprising the original 1929 spans, and replacement spans completed in 1965 and 1989. The structure incorporates unique architectural features, including medallions that honour the First Nations and Metis people who originally used this location to cross the Thunder Creek valley basin and formed extensive trade routes.

In 2006, a Load Evaluation and Strengthening Pre-Design Report indicated that the structure did not have the required load carrying capacity for city buses or fire trucks. This weight restriction also limited plows from clearing snow on the structure. The bridge currently has a 10 ton load limit.

In 2017, the City prioritized the viaduct for repairs to major elements, and in 2020, selected Associated Engineering to complete the preliminary design for the rehabilitation, including project management, communication, and consultation with the Metis, stakeholders, and joint entities including the public. The preliminary design consisted of a detailed condition survey of the bridge, a bridge inspection, concrete deck testing, including chloride testing and cover surveys, followed by recommendation of an appropriate rehabilitation scheme. We used a drone survey to supplement the bridge inspection, as much of the structure was inaccessible without specialized equipment. High resolution images collected with a drone were reviewed by the bridge inspectors.

The team developed a rehabilitation scheme that allows for removing load restrictions on buses and fire trucks. The design also provides a shared-used path on the bridge to improve active transportation facilities. Project Manager, Stephen Chiasson, tells us, “Our bridge rehabilitation concept employs a full-depth concrete overlay and high-performance concrete to replace the existing asphalt. The increase in strength of the deck, along with the removal of the asphalt, increases the load capacity of the structure, allowing for load restrictions to be removed and increasing the service life of the bridge.”

We also undertook a climate change adaptation assessment for the bridge deck drainage. Bridge Engineer-of-Record, Justine Meyers, shares, “Rainfall intensities were developed using a 50-year design horizon to determine increases in rainfall intensity, which were then used to size and space the new deck drains on the bridge.”

The assignment also included a thorough consultation and engagement program with the Metis, stakeholders, and the community, identifying considerations that were important to them, and how these could be incorporated into the design. Issues included traffic accommodation during and after construction, load limits on the bridge, pedestrian facilities, and heritage elements. A heritage review was included to make sure the character defining elements of the structure were respected. Consultation with the Southern Plains Metis Local #160 included their input and feedback into heritage elements.

Transportation planning and stakeholder engagement lead, Ellen McLaughlin, shares, “We undertook a thorough and successful communications and consultation program. During the COVID-19 pandemic, we used a combination of small, socially-distanced workshops, online surveys, social media, pre-recorded communications, and webinars.”

Based on the recommendations in the pre-design report, the City moved ahead with detailed design in 2021. Construction is planned for 2022/2023.

Key team members include Stephen Chiasson, Ellen McLaughlin, Justine Meyers, and Alex Lyon.