Low cover tunnelling under North America's busiest highway

Two new rail tunnels were excavated under the 401/409 Highway in Toronto to increase the capacity of the existing Kitchener rail corridor. The alignment of the new tunnels passes next to the existing Highway 401/409 tunnel and directly under the busiest Highway in North America, which remained operational throughout construction. The sequential excavation method was utilized, combined with 80cm pre-support steel tubes installed from the two portals and an intermediate temporary shaft. The two tunnels, about 10m high and 8.5m wide, were excavated in the fill of the existing highway embankment and the underlying glacial till, with a narrow soil pillar in between. The biggest challenge in this project was assessing and minimizing the impact on the operational highway and existing rail tunnel. The design and construction were successfully completed by the Toronto Tunnel Partners in 2021.