The Île d’Orléans sits proudly in the St. Lawrence River just east of Québec City. Measuring roughly 34 km long and 8 km wide, it was one of the earliest European settlements in North America. Today, its 7,000 residents welcome more than 300,000 visitors each year, drawn by the island’s rural landscapes, heritage villages, and historic churches. At this stretch, the St. Lawrence spans more than 1.5 km across. All access to the island currently relies on a steel truss bridge built in 1935.
To enhance safety, improve mobility, and support long‑term regional growth, the Government of Québec is constructing a new 2.1‑km cable‑stayed bridge, located approximately 120 metres west of the existing structure. The new crossing will include two 3.5‑m traffic lanes and 3‑m-wide multi‑use paths for cyclists and pedestrians on each side. The project’s total value is $2.7 billion CAD.
Understanding the Subsurface: WJ’s Role
The construction team – Dragados Canada and EBC – engaged WJ to investigate the complex subsurface conditions beneath the river. This work is essential for the design of large cofferdams that will support the central cable‑stayed pylons and the approach‑structure piers. Cofferdam stability is a critical design factor due to:
- Deep water, typically more than 30 metres
- Soft underlying sediments
- Powerful river flow, with typical discharge around 12,500 m³/s
- A tidal range exceeding 4 metres
These conditions represent some of the most challenging hydrogeological environments in North America.
Engineering Innovation on the St. Lawrence
To meet these challenges, WJ’s drilling team developed an innovative approach using a floating conductor casing system that could adapt to the river’s tidal fluctuations. This allowed the drilling operation to proceed safely and effectively throughout changing water levels. Thanks to meticulous planning, thoughtful sequencing, and favourable weather, the team successfully installed the full array of wells and piezometers ahead of schedule.
Pump Testing in a Dynamic Environment
WJ then conducted a full pumping test following the company’s standard test procedures – adapted for the unique site constraints and performed entirely from floating equipment positioned above the test locations. Despite strong currents, deep water, and tidal variation, the team maintained stable test conditions and collected high‑quality hydrogeological data. The results will directly inform the final cofferdam design, contributing to the safe and successful construction of this landmark new bridge.
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