Looking Back Creek Bridge
Winnipeg, Manitoba

The Keeyask generation project, located approximately 725 kilometres northeast of Winnipeg, is slated for possible future hydroelectric generation. According to the Keeysak Hydropower Limited Partnership, the project, located in the Split Lake Resource Management Area on the Nelson River will be "a source of renewable energy providing approximately 695 megawatts of capacity and producing an average of 4,400 gigawatt hours of electricity each year. http:// keeyask.com/wp/the-project.

In order to provide for timely construction of the hydro- electric station, should it be approved, the project includes preliminary work on the design and construction of a two-lane access road approximately 25 km in length – part of which includes the construction of a clear span bridge situated at Looking Back Creek. This is necessary to minimize potential environmental impacts and to avoid damaging fish habitat, critical to the First Nations inhabitants in the area.
 
The superstructure is a 30 m clear span structure with a 150 mm thick concrete deck that is designed to act compositely with the 1200 mm deep precast prestressed concrete box girders. According to Marco Suzio, senior sales representative, Armtec, "Due to the northern Manitoba site, challenges included the design to accommodate heavy vehicular loads, shipping and erecting girders, permafrost protection, and protection of a sensitive environmental site."
Indeed, due to the anticipated transport of heavy transformers, the design loads included the worst- case scenario (close to twice that of a typical highway truck design) of a 136,365 kg capacity articulating low-bed tractor trailer – the load is distributed over six axles, the heaviest of which would transfer up to 480 kN live load. Permafrost considerations included provisions during construction to accommodate a 500 ton crane for girder erection, as well as protection of the permafrost layer during serviceability of the bridge to accommodate anticipated long-term settlement. Construction started in March 2012 and was completed in January 2013.
 
Social, economic, environmental impact
The 12 precast concrete box girders measuring 30.3 m x 1.2 m x 1.2 m covered a total area of 436 square metres and eliminated the need for formwork and scaffolding, which helped to meet the challenge of reducing environmental impact to the surrounding area and creek. Precast concrete was the perfect solution for this project as precast elements were readily delivered to the site on an as-needed basis.
This fast, clear span construction method helps reduce the impact on the environment and damage to the fish habitation. Key to the success was the development of a Construction Phase Environmental Protection Plan (CPEPP), which required the contractor to adhere to an enforced environmental protection plan throughout the project.
 
The new bridge has a minimum design life of 75 years and includes a jointless bridge deck intended to reduce future maintenance costs and therefore future disruptions to the public. More importantly, it also ensures that the bridge owner can utilize their limited maintenance, human, and financial assets elsewhere.

Owner:
Manitoba Hydro
Project Description:
Keeyask Generation Project
Engineer:
Dillon Consulting Limited
Contractor:
Mikisiw Construction
Precast Supplier:
Armtec
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