Port of Montreal: Alexandra Wharf

The project is also essential to meet the expectations of citizens who seek better access to the St. Laurence River and to support the growing cruise industry. The economic benefits of that sector totalled $140M for the province in 2012, with close to 55,000 passengers passing through the terminal. With the new wharf, the objective is to surpass the 100,000-passenger mark in less than 10 years.

The Alexandra Wharf was originally built in 1901, with the hangars being added in 1908. The Passenger Terminal was then updated in 1967, for Montreal’s Expo 67. Since 2005, there have been a number of studies and measures taken to stabilize the hundred-year-old structure. Despite the major investment in maintenance and repair, however, the infrastructure was showing marked signs of aging and the facilities themselves were beginning to turn the corner from outdated to obsolete.

Thus, a rehabilitation project was launched and in February 2015, WSP was brought on board to take the designs of Montreal-based architecture firm Provencher Roy for the upgraded wharf, the terminal upgrade, and the lighthouse-like observation tower, and make it a reality. We performed the detailed engineering for the project, including the lowering of the North-East corner of the pier and the design of steps and the lower terrace, which will be partially submerged depending on the time of year.

WSP carried out the structural analysis of existing structures, the design of the new structures and the detailed plans and specifications, as well as carrying out the technical support during construction. Since the site was in an urban area that had to be accessed through the downtown core, special noise-control criteria were implemented and respected throughout construction.

Our first step after winning the project was to complete 3D designs and renderings of the site, in order to allow members of the team to see what the project would look like at various stages of construction. It also helped with the design of the asymmetrical geometry of the lower terrace, so that all conflicts in the plan could be resolved prior to construction.

The biggest complication in this project was the history of the wharf itself: it was built at the end of the 1800s and then altered during a reconstruction project in the 1940s. During these modifications, the mooring mechanisms that allowed the wharf to remain steady even as the river flows around it had been buried. That complicated the works because in order to lower the North-East corner, it was necessary to dig out the anchors - but in doing so, the soil would become unstable.  Therefore, before the digging could begin, it was crucial to stabilize the soil.

It was this North-East corner in particular which posed the greatest challenge and required the most ingenuity. The construction of the below-water wharf wall, however, that required both creativity and extraordinary precision. It had to be designed so that it could be constructed sight unseen underwater, where visibility is massively impaired. 

The construction methods were therefore precisely determined during the design stage. Due to the fact that the construction had to be conducted under the water level, a combined wall structure made of sheet piles and caissons was chosen. This type of structure can be built in difficult conditions while providing structural stability and durability.

In order to accommodate the lowering of the North-East corner, the plan also required drilling through the existing wooden crib that was part of the original hundred-year-old structure. In order to install the rock anchors that will moor the end of the wall, they had to be run through the original, 19th century caissons, which are constructed of 1x1ft hardwood posts. In order to drill through, a special coring drill machine was required. 

Despite the great challenge posed by the construction of this partially submerged wharf structure, the work was completed within the budget and time frame planned. The site will be ready for the 2017 cruise ship season opener and for the festivities surrounding the 375th anniversary of the city of Montreal.

The project was featured in the July 2016 edition of American Society of Civil Engineers (ASCE).