Glenmore Trail Interchange
For over a decade the City of Calgary wanted to do something to ease the traffic congestion that was holding up 70,000 vehicles a day at the intersection of an expressway -- Glenmore Trail -- with 37 Street SW. The junction in the southwest of...
For over a decade the City of Calgary wanted to do something to ease the traffic congestion that was holding up 70,000 vehicles a day at the intersection of an expressway — Glenmore Trail — with 37 Street SW. The junction in the southwest of the city was controlled by signals, which led to long line-ups of vehicles on either side.
In 2009, the city contracted ISL Engineering and Land Services and CH2M HILL to plan and design a grade separated interchange at the “G37” junction. However, problems arose because Glenmore Trail may eventually become part of the southwest ring road being completed around Calgary. The ring road is owned by the province, and with the southeast section under construction only the southwest quadrant remains to be built.
The uncertainty about the Glenmore Trail and 37 Street intersection meant there was a risk that if an interchange was constructed, it might soon have to be removed to make way for the ring road’s final design. The new interchange could become just a throwaway.
Disassembly and reuse
As a solution ISL/CH2M HILL developed a plan to construct a temporary, low-cost bridge over Glenmore Trail about 250 metres to the east of the existing junction i.e. away from the critical land area. The two-lane bridge, approximately 44 metres long, is accessed by two roundabout ramps.
This simple plan had practical advantages. The flyover will serve as a detour for traffic when the final plans are available for this intersection; the design can be re-used, and the bridge itself was designed to be disassembled and reused.
By April 2010 Calgary City Council had approved the plans for the temporary overpass and the project was begun. Design to completion took only five months. The bridge superstructure itself was constructed in just 23 days. It opened on September 11 that year — a record time for an interchange in Calgary.
The speed of the project was partly due to design innovations, but was also due to the way the project was managed, which involved partnering and “integrated project delivery.” Dr. George Jergeas, P.Eng. of the University of Calgary was the facilitator for this process.
With other project delivery approaches such as design-bid-build, the parties are first concerned with identifying and mitigating every risk as it affects them. But on this project the focus was on sharing the risks as a whole, and on first identifying and agreeing on the project goals and how to achieve them together. Regular “health check” meetings were held to maintain the trust between the team.
Risks were shared. For example, a high voltage transmission line needed to be relocated, but the timetable for approving the relocation by the Alberta Utilities Board was not known at the time construction proposal calls went out. Consequently, the construction contract provided for a time extension without costs if the utilities board did not grant the application.
Importantly, as soon as the contractor and subcontractors were selected they were involved in the design and worked with the client and consultants to pool their expertise.
Spread footings, surplus girders and precast panels
Because the interchange is a temporary structure, the design team found important ways of saving time and costs.
First, they founded the bridge on spread footings that rest on mechanically stabilized earth (MSE) embankments. The earth is stabilized using a geo-grid mesh. This approach eliminated the need for constructing pile foundations and abutment walls — elements that would have had to remain behind after the bridge is disassembled.
Second, the design team knew of some surplus pre-stressed concrete girders that were available. With minor remedial work, these were well suited to the temporary interchange. The design was configured to adapt to the girders.
Third, the design uses full-depth, full-width precast concrete deck panels. The deck is over 19 metres wide, and each panel is 19.3 by 2.5 metres in plan by 225 millimetres thick. The panels are set in place quickly and are attached individually to the girders, with small closure pours at the joints.
Reduced exhaust fumes
Today, commuters in Calgary have their journey cut by an average of seven minutes thanks to the temporary overpass. The associated exhaust emissions from idling vehicles have been eliminated.
Calgary has a bridge that can be “recycled” and used at another location when needed. The project also shows how quickly and effectively a construction project can proceed when the different players agree to work collaboratively. cce
CH2M HILL Canada (Andrew Boucher, P. Eng.)
Other key players:
Enmax Power Services (street lights/ HV transmission line relocation; Lafarge (construction); Armtec (precast girder and deck panel fabrication and installation)PCLThurber EngineeringDr. George Jergeas, P. Eng., University of CalgaryISL Engineering and Land Services (Calvin T. McClary, P. Eng., Jim Hanley, P. Eng.) ;City of Calgary, Transportation Infrastructure