Opportunity
In 1939, an airport was constructed on the westernmost end of a small chain of islands that shelter the harbor of Toronto. Known as the Port George VI Island Airport and Toronto City Centre Airport, it was later renamed for Air Marshal Billy Bishop, a Canadian flying ace from World War I.
Originally planned as Toronto’s principal airport, Billy Bishop lost its position to Malton Airport (later renamed Toronto Pearson Airport), which was built around the same time. By 2011 the Billy Bishop Airport was used by 1.55 million passengers, a fifty-fold increase over 2006. Billy Bishop is ranked as Canada’s ninth busiest airport.
By the third quarter of 2010, the ferry serving the island was at capacity. A new and larger ferry, the 200-passenger, Marilyn Bell I, named after the first woman to swim across Lake Ontario, went into service. The ferry continues to leave the mainland and cross the 400-foot (122-meter) Western Gap every 15 minutes from 5:15 a.m. to midnight, with the 150-passenger David Hornell V.C. as a backup.
Construction for a tunnel to the island began in 1935, but the project was stopped and the tunnel filled in when funding ended.
Solution
We began working at the airport in 1997, and in 2010 the joint venture was retained as a subconsultant on a new $82M project to create a pedestrian tunnel from Eireann Quay, at the foot of Bathurst Street, to the airport. As the owner’s engineer on this public-private partnership (P3), we provided reference design and other engineering services.
With a length of about 656 feet (200 meters) and a width of 32 feet (10m), the pedestrian tunnel has one of the biggest cross-sections of any tunnel in the city. The local shale bedrock posed a challenge to construction, especially since the tunnel would be 85 feet (26m) deep. The shaft on the mainland end of the tunnel passes within about three feet (one meter) of a historic crib wall constructed of timber and filled with rubble.
The shafts were built using the secant wall method, which uses interlocking concrete cylinders to provide stability during excavation. The tunnel was bored using a roadheader. An electrically powered concrete batch assembly was used to reduce the need for concrete delivery and therefore noise, dust, exhaust, and traffic congestion.
Outcome
Elevators on the mainland side and an escalator on the airport side lower travelers to the tunnels, where walkways equipped with automated people movers will take them to and from the island.
Mark McQueen of the port authority said the project would improve reliability of access and maintain a high standard of customer service for passengers. Finance minister James Flaherty said, “Less time spent in an airport or waiting for a ferry means more time creating jobs and economic growth for business travelers, and more time with friends and family for those traveling for personal reasons.”
The pedestrian tunnel was also designed to carry water and sewage mains that will serve Toronto Island, saving the city of Toronto more than CDN $10 million.
Award
The tunnel was named the 2014 Canadian Project of the Year by the Tunnelling Association of Canada.