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Four massive tunnel boring machines will dig the 15km twin tunnels on Sydney's North West Rail Link. The first TBM will be in the ground in October, 2014 at the Bella Vista tunnelling site. The TBMs are a feat of modern engineering and are currently under construction. Watch how all the pieces are assembled, tested, pulled apart then re-assembled before digging can start. The $8.3 billion North West Rail Link is due to open to customers by the end of 2019.