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Metro Tunnel

Early Works construction methods

Shaft construction

Two shafts will be excavated as part of the CBD North early works program. These will be located at Franklin Street between Swanston and Victoria streets and A'Beckett Street between Swanston and Stewart streets.

The process for shaft building will include:

Piling

Piling is a common technique used to bore steel and concrete support structures below ground that create the supporting walls for excavations, such as the tunnel shaft. It will also be used to construct the footings of acoustic sheds and noise hoardings around the project sites.

Excavation and propping

The main proposed method of excavating the shaft will include breaking the ground at 2.5 metre depths and excavating the material/spoil. Once the material is excavated a steel prop will be installed to support the piled walls and the process would start again until the required depth is met.

Acoustic sheds

Temporary acoustic sheds will be built to enclose the shaft excavation. Acoustic sheds are commonly used during construction of tunnels to minimise noise, light and dust spill on the local community during 24-hour tunnelling activities. The walls of the sheds include acoustic insulation and will be custom built for each site.

How will the services be relocated?

Service relocations will be completed using two techniques.

Open cut trenching

The traditional and most popular method for service installation, repair, or replacement. Open cut trench excavation consists of excavating a trench for the manual installation of each piece of pipe. 

The open cut trench method involves excavating down to the required depth, installing or replacing the service, backfilling and reinstating the area.

Boring

A trenchless method of installing underground pipe, conduit, or cable along a prescribed bore path by using a surface-launched drilling rig, with minimal impact on the surrounding area.

It is suitable for a variety of soil conditions and is used for crossing waterways, roadways, congested areas, environmentally sensitive areas, and areas where other methods are not possible.