How is the tunnel likely to be built?
Three main techniques will likely be used for tunnel and station construction, depending on geological conditions and facilities needed at street level such as station entrances and vent shafts. The construction methods are tunnel boring, cut-and-cover and mining. Tunnel Boring: It is anticipated that much of the downtown tunnel will be built using tunnel boring technology in which a circular cutting machine drills a tunnel in rock or soil with minimal disruption to the street. The excavated material is then taken to the launch site at the west end of the tunnel where it will be removed by truck. Cut-and-Cover: With cut-and-cover construction, a trench is cut in the street, the soil is supported by vertical walls and a frame is built to support steel beams and wooden decking to cover over the cut. The decking allows the street to remain open to traffic and pedestrians while excavation and construction continue below. Cut-and-cover may be used at certain station locations and for sectio
