Port Mann Main Water Supply Tunnel
Summary
The Port Mann Main Water Supply Tunnel increased Metro Vancouver’s capacity to accommodate future regional growth while also improving overall system reliability. The project included construction of a 1,006-meter-long (3,300 ft) water supply tunnel under the Fraser River between Coquitlam and Surrey in British Columbia, Canada. This new, larger water main helps ensure the continued, reliable delivery of clean, safe drinking water, and more than doubles the capacity of the existing main.
The tunnel, mined between two 64-meter-deep (210 ft) vertical shafts, was constructed using earth pressure balance (EPB) methods, is approximately 3.5 meters (11.5 ft) in diameter, and contains a new 2.1‑meter (7 ft) internal diameter water main. The tunnel alignment is located below the depth of riverbed scour and is designed to remain functional following a maximum credible earthquake (MCE) event. The tunnel ties into the existing Metro Vancouver system on the north and south banks of the Fraser River.
- 1,006-meter-long (3,300 ft) water supply tunnel
- Two 64-meter-deep (210 ft) vertical shafts
- Pressurized face tunneling
Scope of Work
The project construction was a joint venture of McNally and AECON and was designed by the Fraser River Tunnel Group (consisting of Ausenco Sandwell, Delve Underground, and Golder Associates), while Metro Vancouver retained Hatch Mott MacDonald as the construction manager. Delve Underground’s services included review of the preliminary design and confirmed alignment, detailed design of shafts and tunnel, and engineering services during construction.
Challenges & Innovations
The 3.5-meter-diameter (11.5 ft) Caterpillar EPB TBM, “Squirrel,” encountered challenging ground conditions with artesian groundwater producing up to 6 bar of pressure, the highest in Canada at the time for TBM tunneling. Delve Underground worked closely with the rest of the project team and provided expert tunnel engineering consultation to overcome the challenges of excavating through the bouldery glacial till.
In addition, during construction, Delve Underground collected geotechnical instrumentation data, processed/managed the data, reported results to the team, and provided interpretation. The program included survey points, inclinometers, extensometers, liquid settlement monitoring points, and deeper utility settlement points, and was essential for observing the performance of the tunneling and shaft excavation process on the north and south sides of the Fraser River.