Re:Elon Musk’s Boring Co. Wins Chicago Airport High-Speed Tr...
by theptip on Thursday June 14, 2018 @01:25AM
(#17309506)
While I like what The Boring Company is doing, and I personally aspire to one day found a multimillion dollar company based on a joke, I've always found this claim to be a bit disingenuous.
A large part of the "10x faster" claim is from a 4x speedup from drilling a 4x smaller hole. That's not a boring machine improvement, anyone could drill such a hole with an existing machine. (I've heard the claim "10x cheaper" too). If you make a smaller tunnel with lower throughput than a subway, then you need more of them, so it's not clear to me that you can claim a speed improvement just because you can do one of your tunnels faster. Indeed if you more than halve the throughput by halving the tunnel cross-sectional area, and halving the boring time, then you've made the whole system more time consuming to create.
Another claim is that current tunnel boring machines (TBMs) stop for 50% of the time, to allow the supports to be put in; this will give them another 2x speedup. However a cursory Google search (I'm not an expert in this field) shows that the technology for continuous TBMs already exists [1]. That reference contains a very in-depth video if you want to see exactly how these things work, it's very cool. This machine can apparently do 2.8-12.5m diameter holes, which covers the diameter that TBC is targeting. (As I've fact-checked this point further, the Boring Company's website makes the more restricted claim [2] that "current soft-soil machines tunnel for 50% of the time"; maybe the overly broad claim came from misquotes in the press and not from TBC themselves. I haven't found any soft-soil continuous TBMs yet).
Finally Musk claims that current TBMs are operating well below the thermodynamic maximum, and so he can get another 3x speed boost. On this point I'm not qualified to debate; it seems unlikely that there's that much gain left on the table (surely the TBM companies that currently exist have spent a lot of money plucking the low-hanging fruit of efficiency gains?) but Musk has sent rockets into space so perhaps he knows what he's talking about here.
E.g. https://www.quora.com/Why-does-Elon-Musk-think-he-can-bore-5...
A large part of the "10x faster" claim is from a 4x speedup from drilling a 4x smaller hole. That's not a boring machine improvement, anyone could drill such a hole with an existing machine. (I've heard the claim "10x cheaper" too). If you make a smaller tunnel with lower throughput than a subway, then you need more of them, so it's not clear to me that you can claim a speed improvement just because you can do one of your tunnels faster. Indeed if you more than halve the throughput by halving the tunnel cross-sectional area, and halving the boring time, then you've made the whole system more time consuming to create.
Another claim is that current tunnel boring machines (TBMs) stop for 50% of the time, to allow the supports to be put in; this will give them another 2x speedup. However a cursory Google search (I'm not an expert in this field) shows that the technology for continuous TBMs already exists [1]. That reference contains a very in-depth video if you want to see exactly how these things work, it's very cool. This machine can apparently do 2.8-12.5m diameter holes, which covers the diameter that TBC is targeting. (As I've fact-checked this point further, the Boring Company's website makes the more restricted claim [2] that "current soft-soil machines tunnel for 50% of the time"; maybe the overly broad claim came from misquotes in the press and not from TBC themselves. I haven't found any soft-soil continuous TBMs yet).
Finally Musk claims that current TBMs are operating well below the thermodynamic maximum, and so he can get another 3x speed boost. On this point I'm not qualified to debate; it seems unlikely that there's that much gain left on the table (surely the TBM companies that currently exist have spent a lot of money plucking the low-hanging fruit of efficiency gains?) but Musk has sent rockets into space so perhaps he knows what he's talking about here.
[1]: https://www.herrenknecht.com/en/products/core-products/tunne... [2]: https://www.boringcompany.com/faq/