On July 30, 2015, travelers catching a flight out of Billy Bishop Airport became the first passengers to descend below Lake Ontario to experience the engineering feat of one of the world’s first fully underwater tunnels from a mainland to an island airport, now open in downtown Toronto.
The project, which broke ground in 2012, included excavation of vertical shafts on both the mainland and island sides. At 190 m in length, and 6 m high by 9 m wide, the tunnel is one of the largest to be constructed within the Georgian Bay shale formation of the Greater Toronto Area.
The $82.5 million project was procured by owner-operator PortsToronto as a public-private partnership (P3) structured under a design-build-finance-maintain model with Forum Infrastructure Partners. In this capacity, Forum acted as lead developer, with PCL Constructors Canada Inc. as design-builder, Arup as lead designer, Technicore Underground Inc. as tunnel contractor, and Johnson Controls as facility manager. In collaboration with design-build lead PCL, Arup was the lead tunnel designer for the project, including the temporary support and the permanent lining design, and also provided technical support and general review services during construction.
“Arup developed the design to meet PortsToronto’s aim for a world-class facility while working closely with project partners to make the tunnel efficient to build and operate,” said Jon Hurt, principal of Arup. “As lead designers, we accessed the full extent of our resources to design a project that has successfully accomplished an underwater pedestrian airport tunnel for the first time in this region.”
The team used innovative solutions to combat construction challenges, which included site and weather conditions, the logistics of building adjacent to an operational airport, excavating through shale, as well as the infinite water source present from Lake Ontario.
The team pioneered use of an innovative pre-support technique using seven interlocking horizontal bores, drilled by two tunnel boring machines and backfilled with fluid concrete. This permitted safe excavation of the main tunnel. Once the tunnel’s pre-support arch was in place, mass excavation began. To validate the tunnel’s structural design, the team utilized advanced computer and numerical analyses to simulate nonlinear, time and stress dependent swelling behavior of the shale rock, combined with a rigorous shaft and tunnel deformation monitoring program.
The project has been recognized with several prestigious awards, including the Specialist Tunnelling Project of the Year by the International Tunnelling and Underground Space Association, as well as the Canadian Project of the Year by the Tunnelling Association of Canada.