Construction : Tunnels

Next: Mitigation

Union Station, 1973 Union Station, 1974 Earth tunneling, early 1970s Rock tunneling, 1980s Prefabricated tunnel, 1977
Click on any thumbnail for a full-size image.
For busy downtown stations, engineers chose cut-and-cover construction for both tunnels and stations. This technique kept stations close to the surface, minimizing both the time needed to enter or exit and the cost of building multiple entrances. In some cases, the avoid surface disruption, the builders bored earth tunnels close to the surface instead. North of downtown, where river bottom gave way to the beginnings of piedmont, they used blasting and enormous “moles” to dig rock tunnels. For the Yellow Line’s trip to Virginia, a tunnel was prefabricated on land and carefully sunk in the Washington Channel.