Bearspaw Pretreatment project wins the ACI Alberta Chapter
2009 Award of Excellence in Concrete

With growing demand for drinking water, limited water supply, and more stringent water quality requirements, the City of Calgary embarked on a program to upgrade the capacity of its Bearspaw Water Treatment Plant, one of the City's two water treatment plants. The City engaged Associated Engineering to design upgrades that would not only meet water demands, but also be innovative and sustainable.

Bearspaw WTP Pretreatment Facility during construction. Inset:Sloping back wall of settling tank.

The Associated Engineering team met this challenge with the design of a new Pretreatment Facility at the Bearspaw Water Treatment Plant. Located at the site of a decommissioned sedimentation basin, construction of the new facility made use of existing land and provided an opportunity to recycle and reuse materials from the demolition of the existing structure. Over 9,000 cubic metres of concrete from the original sedimentation basin was crushed and reused in site roads and as backfill while reinforcing bars removed during the demolition were recycled. The engineering team also made innovative use of specially formulated concrete products to achieve the operational requirements for the water retaining structures and foundations on the project.

For the design of this facility, the Associated Engineering team considered process and functional requirements, architectural impact, geotechnical conditions, structural requirements, 100-year design life, low maintenance, cost, and constructability. As a result, different construction materials and systems were implemented for different parts of the facility to adequately address these issues.

Lead Structural Engineer, Risto Protic advises, “We selected concrete as the preferred material for all below-grade tanks and the foundation structure because of its suitability for construction of water retaining and conveying structures, and its ability to meet unique geometric requirements. We also used concrete for building components where adequate support and rigidity were essential for chemical storage, proper equipment operation, and vibration control.”

A combination of steel fabrications and concrete block masonry proved to be the most cost effective and suitable material choice for the superstructure. As part of the landscape treatment around the facility, modular concrete block masonry units were used for retaining walls. Due to varied geotechnical conditions and unstable characteristics of volcanic ash layers at the project site, the team decided that the Pretreatment facility would be founded on cast-in-place rock-socketed piles. Over 380, 900 millimetre diameter reinforced concrete piles, varying in length from 10 to 15 metres and loaded up to 2700 kilonewtons were constructed to support this facility.

To promote quick settlement of flocculated particles, the settling tank walls were sloped at 55 degrees, which provided some challenges for construction. To achieve a good finished product, the design team used about 350 cubic metres of self-consolidated concrete (SCC) for this application. This specially formulated concrete mix provided good flow characteristics and reduced the risk of segregation without the need for vibration, proving to be the right material for the job.

Construction brought many challenges, most notably the following:

• Complex arrangement of clarified water conduits that were stacked on top of one another to allow for independent operation of the East and West clarification trains
• Water tightness of structures required that all construction and expansion joints be detailed with continuous PVC water stops
• Numerous pipe penetrations, openings, and flow control features such as weirs and stop logs had to be accommodated throughout the process.

Through carefully specified concrete materials, attention to detail, and quality workmanship the project team achieved a functional and efficient structure that meets the City's requirements.

The Bearspaw Pretreatment project recently received the ACI Alberta Chapter 2009 Award of Excellence in Concrete.

Receiving the ACI Alberta Chapter 2009 Award of Excellence in Concrete: (L-R) Colin Hill (PCL), Kelsey Kundert (City of Calgary), Bill Lenz (Lafarge), Glen Tetarenko (PCL), Steven Dold (City of Calgary), Dave Winter (AE), Risto Protic (AE), and John Irving (AE).