Environmental Science & Engineering - www.esemag.com - September 2004
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Engineers design unique stormwater duct under urban section of TransCanada Highway

By Michael Chau, City of Calgary and
Randy Giberson, Lafarge Canada Inc.

Installation of box units for underground stormwater storage structure designed using software that helps engineers and specifiers reduce design time and costly over-designs on projects.
Photo: Randy Giberson © 2004
Construction of the Rundle Underground Storage Duct in Calgary, Alberta, was far more than the installation of a unique underground stormwater management structure. Location of the construction site presented a significant challenge to the design engineers since the only space available for the installation was the 22–metre wide median of the east- and west-bound lanes of 16 Avenue N.E. In addition to serving the City as a main east-west artery, 16 Avenue N.E. is also a section of the TransCanada Highway – a major link between eastern and western Canada. Along with the space limitations, the 6.5 to 9.0 metres depth-of-bury was a significant consideration for equipment access and material selection for the structure.

The project consisted of a two-cell (each cell measuring 2400 mm wide x 3000 mm high) concrete duct, 550 metres long with cover up to 5.65 metres over the duct. This would require an excavation depth in excess of 9 metres. The project also included two 2400 mm x 5500 mm cast-inplace maintenance access manholes that connected the two-cell duct to an existing duct with 1800 mm concrete pipe. The maintenance access manholes were located about 100 m from each end of the duct. City of Calgary Wastewater completed the engineering, in collaboration with Mack, Slack and Associates Inc. and EBA Engineering Consultants Ltd., located in Calgary.

It is critical to public safety that structures such as the Rundle stormwater duct not undergo brittle shear failures. If the shear reinforcement in these structures is excessive, however, it is a waste of resources and contrary to principles of sustainable development.
An investigation into shear behaviour of concrete box culverts is being undertaken at the University of Toronto. When completed, the research is expected to have a significant impact on the cost of buried infrastructure and the use of resources for producing precast concrete boxes. But most significantly, the research will have a profound impact on design methodology and principles used in industry and academia for concrete structures.
The 7,200-m3 underground storage structure was built to relieve flooding in northeast Calgary due to severe rainstorm events. Damage from these rainstorms included street and property flooding, basement seepage, manhole lids blowing off, and sanitary backup. Two of the communities most affected by this flooding included Pineridge and Rundle. The Rundle duct will collect stormwater during major rainfalls, detain it, and then slowly release it back to the storm sewer system.

During the project tendering stage, Whissell Contracting asked Lafarge engineers if they could design precast boxes to support an American 5299 fifty-ton crane to place the two parallel lines of box units. The design to support the crane, as well as the final soil backfill, resulted in the precast box culvert option being lower cost than the cast-in-place option.

The production and installation schedules were very important considerations of the project since the City could not close 16 Avenue N.E., and had to keep lane restrictions to a minimum so as not to disrupt traffic. East bound traffic could be reduced to one lane while the second served as a haul road for delivery of the boxes. The east lane had to be re-opened to two lanes during peak times of 3:30 p.m. to 6:00 p.m. Monday through Friday. Work could only occur for ten hours between 7:00 a.m. and 5:00 p.m. Both schedules had to be timed to ensure that product would be available and arrive on-site when required by the crews. There was no room for on-site storage, so just-in-time delivery from Lafarge’s plant 16 kilometres away became critical to the cost of construction.

BoxCar, a software program developed by the U.S. Federal Highway Administration and the American Concrete Pipe Association during the 1990s, was used in the design stage of the precast concrete boxes. The program helps engineers and specifiers reduce design time and costly overdesigns on projects using precast con- crete box units. Deriving its name from box culvert analysis and reinforcing design, this popular interactive program can be used to calculate reinforcing steel areas for user-specified box geometry, material properties, and loading area. The program was used to analyze the precast boxes that would support the crane, the backfill loads of the median and the structural elements of the stormwater storage duct. It was particularly useful for the contractor during the tendering stage of the project to get speedy and accurate answers to critical questions.

To determine the required reinforcing, parameters of the specified boxes were entered into BoxCar, and then Lafarge engineers extracted the load cases applicable to the crane load scenario. The final structural load cases and the steel reinforcement were then designed according to the worst-case load combinations. Design parameters included conditions on the crane such as maximum allowable reach, and the use of crane pads. The analysis also proved that the boxes could be designed with adequate strength for performance and durability without requiring stirrups for shear reinforcement.

The 151-page engineering report summarized for the City of Calgary included all hand calculations, all printouts from BoxCar used in the analysis, and steps taken throughout the analysis.

Work began on March 20, 2003, with preparation of the site for the installation of the boxes. The first box was shipped to the site on April 7 with the last of the 542 arriving on June 13. The contractor was able to install an average of 14 boxes per day of construction. The job was completed June 30, 102 days after start-up. Installation of the boxes took place over 67 days. In the plant, production of the specially designed box units started on February 19, and ended ninety-four days later on May 24.

The design team for the Rundle/16 Avenue N.E. project used engineering principles, contemporary design software, and life cycle cost considerations to ensure an economic and safe project that will serve the people of the area for generations. Resources have to be used wisely – more so than ever before considering the high costs of infrastructure rehabilitation and growth issues facing our cities. The Rundle underground storage duct may be considered a leading-edge project that employed engineering principles that are currently being enhanced by university- based research (see inset) for tackling complex and costly infrastructure projects.

The unique stormwater duct project was partially funded by the Infrastructure Canada-Alberta Program (ICAP). Calgary is eligible to participate in programs up to $123 million. Construction of the Rundle duct was estimated to cost $3.8 million.

Michael Chau, P.Eng., is Project Manager, City of Calgary and
Randy Giberson is Plant Engineer, Lafarge Canada, Greater Calgary Area.
Contact e-mail: randy.giberson@lafarge-na.com.

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