Elon Musk (TED 2017)
ted.com
ted.com
Cost savings breaks down by:
1) Narrower tubes - less cross-sectional area means cheaper tunneling
2) Continuous tunneling/reinforcing - no stops to build tunnel walls. (Seattle's Bertha did this.)
3) More power = faster execution (not clear on details of this one)
Seems not to address different materials/geology in different depths. Also, no mention of regulatory burdens to approve digging underneath existing property rights. (two things I know nothing about)An interesting takeaway: He wants to dig tunnels because he doesn't believe in flying "cars" which would make feel people uncomfortable. Interesting antithesis to what his peers in the tech world are doing.
I just don't see a future for them outside of billionaires play things.