>What impresses me most about TBC is how fast they were able to dig a tunnel. Well, "normal" small diameter TBM's in "normal" terrain/rock can go as fast as 40

>What impresses me most about TBC is how fast they were able to dig a tunnel. Well, "normal" small diameter TBM's in "normal" terrain/rock can go as fast as 400 m/month ("net" progress rate) to this you add some time for preparation and assembling of the machine (and some time for disassembling after the actual bore is finished), a good "average" is 240-280 m/month. To be fair both the Seattle and the Hawthorne projects are way shorter than what a TBM is usually used for (i.e. preparation/assembling has a larger weight on project times). If the "boring Company" started it in January 2017 and will end it in December 2018 it is 3200 m in 23 months, i.e. 140 m/month (including the assembling/preparation), not particularly impressive. Bertha is another story, it is "huge", 17.4 m in diameter, the Hawthorne project TBM (called "Godot") is only a 4.2 m one (around the minimal size of TBM), it helps to compare the cross section area, 8.7^2xPi=237 sqm, 2.1^2xPi=13.9 sqm. In any case the Seattle project is (in)famous for the steel pipe that allegedly broke Bertha's main bearings sealings, once it was repaired it dig quite fast, after all (and given its size), 2830-330=2500 m in 15 months is roughly 170 m/month.