I think you should read this. It may sound funny but actually it is not. It is very sad. A railway route with two parallel tunnels in Rome, Italy has been abandened with its tunnel boring machines, cutter heads and everything else, just several steps from its completion, because `the city runs out of money'.

The railway route called "Line C" comes from the suburbs to the heart of the city brushing past the famed Colosseum, was to be reaching Piazza Venezia and then going under the river of Tiber. But because of "cost overruns partly because of ancient remains and corruption (Italy !)" the city could not find the 790m Euro required for the last run. So, the construction stops a few hundred past the Colloseum. Sad really.

Although according to the newspaper, the project's head Andrea Sciotti says "They will shore up the end of the twin tunnels and stop water infiltration, meaning they can never be used again”, looks like any future attempt to restart the tunneling should start from the other end and when it meets the abondoned tunnel, there will be the daunting task of boring or rather cutting through the buried TBM's cutter head...

https://www.thetimes.co.uk/article/what-a-bore-rome-buries-its-drills-bptmzkb2t