By: Atlantic Industries Limited
The initial need began back in 2013 when a 2,000 acre commercial development in St. John’s, NL identified a future requirement for access to the Trans Canada Highway, which would require an underpass structure. AIL provided multiple options over the course of a 10-year period with different consultants. Finally, in 2021 NL DTI had decided that this project would be tendered for construction in 2023.
In 2021 there was an RFP for design services tendered for this interchange project. AIL provided each consultant bidding this RFP with a detailed proposal for a Structural Plate Low Profile Arch Underpass. AIL then proceeded to work closely with the owner as they were analyzing the benefits of a Low-Profile SCSP Arch against concrete girder bridge options. Ultimately the owner chose the SCSP arch as the preferred option, as it provided multiple benefits including lower constructed cost, reduced social impact due to construction timelines and lower maintenance costs for the lifetime of the structure.
During the design phase AIL worked closely with the owner to discuss the benefits of including resilient design features such as incorporating a waterproofing membrane above the arch and including a concrete splash wall. The owner decided to include both features in the final design to mitigate road salt contact with the arch.
The final geometry was chosen was a 83.44′ Span x 21.05′ Rise x 141.08′ Long Low-Profile Arch. The geometry allowed for a 4-lane vehicular clearance box with center median barrier (49.2126 ft Wide x 16.4042 ft High), plus additional clearance boxes on each side of the structure (9.84′ wide x 8.89′ high) for recreational vehicle access. The arch was a square end structure utilizing MSE precast face headwalls and wing walls.
Construction of the arch went very well, with the contractor taking just 7 days to erect all 215 plates.
The structure is currently backfilled and is expected to be in commission for the summer of 2024.
The interchange site is also at the entrance to St. John’s largest construction quarry and ready-mix plant on the opposite side of the TCH. Trucks now travel an extra 3.12 mile loop to access the highway. Once operational the new interchange will provide a reduction of truck traffic by approximately 16,156 miles per year, which translates into approximately 42 tons of CO2 emissions (EPA Emission Factors 2023).
Project Video: https://youtu.be/bxYP7npX75g