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Comment by Rescis | Hacker News Reader

Several hundred million dollars at best gets you a mile of subway in an American city: https://www.vox.com/22534714/rail-roads-infrastructure-costs...

Experimentation with alternatives is desperately needed.

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His whole thing for a while was how it was going to be cheaper to dig tunnels by using new techniques etc, that would equally apply to subways - but a feel like it was probably bullshit.

The new technology is smaller drills that make smaller tunnels.

They are electric and can start at street level and dig themselves down.

This is ridiculous misinformation. "Drills" come in every size already, from the 12-inch range all the way up to 60 feet in diameter. All modern "drills" that erect a liner behind them are electric - air quality and safety issues (along with the massive energy requirements) mandate the use of an umbilical from the surface and prevent the use of diesel or gas in the tunnel for these machines. None of Boring Company's "drills" are able to start at street level and dig themselves down, they require a ramp or shaft just like every other TBM. This is physics, the Boring Company has made no technological advances. They literally bought their TBM from someone else and put it in the ground with a new paint job.

Here are pictures of the drills launching at ground level and digging themselves down [1], and a third party source discussing it as an innovation in boring [2]

https://www.boringcompany.com/prufrock

https://www.construction-europe.com/news/6-ways-tunnel-borin... -evolving/8026001.article

This would be called a launch ramp in the industry. It is an adaptation of HDD approaches to larger diameter machines. It has been going on for decades. It is only viable where space and the final geometric constraints of the project permit. Additionally, it requires very specific geologic conditions or the construction of a structural headwall in order to avoid a sinkhole.

For example, what Boring Company is doing has already been done in the extreme limit: Herrenknecht sells a vertical shaft boring machine that is essentially a TBM turned 90 degrees. https://www.herrenknecht.com/en/products/productdetail/verti...

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