Main Street Tunnel Main Street Tunnel The Main Street Tunnel, located in Welland, Ontario, Canada, is an underwater tunnel, carrying Niagara Road 27 and the unsigned designation of Highway 7146 under the Welland Canal. It is named as a part of East Main Street. The structure was built as a part of the Welland By-Pass project. Its construction was relatively easy since, like the Townline Tunnel, it was constructed at the same time as the channel above it and a simple cut and cover. The tunnel was officially opened on May 20, 1972. The tunnel links Highway 406 on the west side of
Channel Tunnel techniques from the oil industry were employed. Tunnelling was a major engineering challenge, with the only precedent being the undersea Seikan Tunnel in Japan, which opened in 1988. A serious risk with underwater tunnels is major water inflow due to the pressure from the sea above, under weak ground conditions. The tunnel also had the challenge of time: being privately funded, early financial return was paramount. The objective was to construct two rail tunnels, apart, in length; a service tunnel between the two main ones; pairs of cross-passages linking the rail tunnels to the service one at spacing; piston relief