Chatswood to Sydenham

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The Chatswood to Sydenham component of Sydney Metro City & Southwest involves the construction and operation of a new metro rail line from Chatswood under Sydney Harbour and through Sydney’s CBD out to Sydenham.

Tunnelling under Sydney Harbour

A specialised tunnel boring machine (TBM) designed for the geological conditions under Sydney Harbour excavated twin metro rail tunnels from Barangaroo to Blues Point.

Sydney tunnel depths

Diagram showing specialised tunnel boring machine. This machine will combine two types of TBM technology into one, allowing tunnel builders the flexibility to adapt to different ground conditions as the machine progresses. The two modes are 'earth pressure balance' mode - which uses a screw conveyor and valve to control the pressure by regulating the amount of spoil in the macdhine. Used for rock conditions. The other mode is 'slurry' mode - which uses pipes and fluid to control the pressure in the machine,

A specialised TBM was used to tunnel under Sydney Harbour

Infographic: Retrieving a TBM at Blues Point. 1. Excavation of a shaft to tunnel level. In 12 months, excavators and other equipment used to dig shaft to tunnel level. 2. Extraction of tunnel boring machine. TBM is dismantled and removed via the shaft using a crane, TBM cuts through to tunnel shaft. This process takes 1 month per TBM. 3. Shaft will be backfilled and parkland reinstated. Once TBMs have been removed the site will be returned to the community with no further use by the project (3 months).

How we retrieved the TBMs at Blues Point

Building the tunnels

TBMs were used to excavate 15.5 kilometres of new twin rail tunnels between Chatswood and Sydenham.

Sydney Metro City & Southwest required five TBMs. Two were launched and removed from the Chatswood and Marrickville dives sites, with the fifth from Barangaroo.

Building the stations

The new underground stations on Stage 2 of Sydney Metro are designed to be as close to the surface as possible to allow customers to get in and out easily. At Crows Nest, Barangaroo, Central and Waterloo the stations will be excavated from the surface in a cut-and-cover construction method. At Victoria Cross, Martin Place and Pitt Street the station caverns will be mined out underground.