The State Government last month announced it would use tunnel-boring machinery to construct the proposed Metro Rail tunnels under the Yarra River.
Transport Minister Jacinta Allan said other methods had been considered, but that tunneling would create the least disruption.
“Tunnelling under the Yarra will reduce disruption to the environment and to local businesses,” Ms Allan said.
Other techniques would significantly disrupt the river and its surrounds by either damming or creating an immersed tube tunnel, which would require dredging the river bed.
The Government had previously announced the use of tunneling machines under Swanston St between Collins and Latrobe streets.
Tunnel boring machines allow for excavation through varying ground conditions and have specialised cutting heads designed to grind through soil and rock, with minimal impact on the surrounding environment.
The machines also enable the excavated tunnel to be immediately sealed with a concrete lining.
The tunnel will be 11 metres below the surface and will sit to the east of Princes Bridge, around seven metres below the riverbed.
The details of the final location, design and construction methodology for the tunnels will be determined by the appointed construction contractor.
Melbourne Metro will deliver two new nine km rail tunnels and five new stations.