Pomerleau supplied all the necessary services to construct an underwater retaining wall in order to stabilize and deepen 650 linear metres of berths in the Port of Montreal, Racine Terminal. Pomerleau was also responsible for the procurement of materials.
Over the years, the berths' caissons have been worn away, due mainly to the rising number of ships equipped with side docking propellers, and this had compromised the stability of the offloading areas. As the new ships that will be coming to Montreal in the near future draw more water, the berths also had to be deepened. It was therefore necessary to construct a new underwater retaining wall, mainly in imbricated sheet piling, all along the existing caissons. This was a first in Quebec.
Before building the retaining wall at a depth of 13 m, Pomerleau's team demolished and removed all the existing underwater structures and obstructions. We then deepened and stabilized the berths, using three types of structures: sheet pilings driven into the overburden, sheet pilings anchored by piles and trimmed down concrete foundations.
Sheet piling driven into the overburden was the structure of choice. However, where the bedrock did not allow the sheet piles to be driven in far enough to reach the minimum required depth, we used a composite wall of piles and sheet piling. Embedded 2.5 m deep and concreted into the rock, these piles are the bearing elements. Connectors were welded to them so that so that the sheet pilings could be attached on both sides.
The installation of the compound wall and concreting the fixed ends of the piles underwater proved to be one of the project's most complex steps. We had to design several custom tools to perform this work, chiefly templates, a support and lift device and special concrete hoppers.
The existing concrete foundations were kept as protective elements but were cut down far enough to be out of the way of the ships' hulls.
- The depths at which the work was executed and the degree of precision required were the main contributors to the complexity of the project. These same factors also make this type of underwater work unique.Pomerleau employed three teams of four divers each to ensure an underwater presence at all times.
- Our team had to make a number of custom tools, chief among them were pile driving templates, followers, support and lifting devices and special hoppers to send less than 1 m3 of concrete per pile down 28 m from the wharf to the bottom of the fixed ends of the piles.
- Most of the work was completed during the winter of 2002-2003. The extremely cold temperatures that year presented significant challenges.
- From the surface, nothing looks any different as the entire finished project rests on the riverbed.