For the demolition of thirty (30) spans of the northern portion of the bridge, the work entailed a very challenging level of planning and engineering to ensure the safe and successful execution of this part of the overall project. Each span—having a length of 53.7 m and a width of 24.1 m—was supported on concrete piers that varied in height from 10 to 28 m. The design of the demolition methodology needed to take into consideration several constraints including the type of construction, which prevented the spans from being demolished using “traditional” approaches, due to not only the lack of reinforcing steel in the girders but also the poor condition of the post-tensioning cables. “The St. Lawrence River, which is a protected environment for wildlife and a source of drinking water for millions of people, was also central to the design process since no debris was allowed to fall into the water and explosives were not permitted,” says Hebert. Although the river is more than 3 km wide from one bank to the other, its depth varies widely from only 1.5 m in some places to more than 8 m in others. This factor along with the high current speed of the river near the bridge, which can reach more than 5 knots, and the extremely cold weather conditions that can occur during winter, were other important design constraints that affected the choice of maritime equipment, access to the structure, and the overall execution of the work. The final methodology that was designed and engineered by the team involved removing the whole span, which weighed about 2,000 tonnes, in 24 AUG 2023 | BUSINESS ELITE CANADA
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