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Getting the job done! Discover how tunnel boring machines (TBM) operate


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They are the heavy lifters when it comes to building the Sydney Metro railway tunnels, but aside from crushing rock like nobody’s business what else does a TBM do? We find out…

Major tunnelling is underway on both the Sydney Metro – Western Sydney Airport and Sydney Metro West projects. Both mega projects require underground metro tunnels to be constructed. 

The mammoth task of building the twin metro tunnels for both projects is the job of 10 TBMs – all four TBMs are already tunnelling to build the Airport metro tunnels and three of six TBMs are currently constructing the Metro West tunnels. 

The operations of a TBM include:

1. The cutterhead at the front of the TBM spins and as it does, high-steel alloy steel discs extend out to the rock surface and crush the material in its path.

2. Crushed rock is scooped into the machine’s head and onto a conveyor belt.

3. The conveyor moves rock through the machine and out of the tunnel behind it.

4. Concrete ring segments are delivered to the ring building area.

5. Concrete ring segments are fixed onto the tunnel wall carved out by the TBM using a special vacuum lifting device.

6. When completed, the ring is connected to the previously-built ring.

7. The gap between the concrete ring and the rock is filled with grout – this helps keep water out of the tunnel.

A total of six concrete segments make up one concrete tunnel ring.  

Once the TBM finishes building the fully lined tunnel, it breaks through a rock wall to arrive at its destination where it is then retrieved.

Sydney Metro TBMs work around the clock and build up to 200-metres of new tunnel every week. 

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