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Digging a new tunnel immediately underneath an old tunnel is going to introduce different stresses on the old tunnel So then dig the new tunnel beside it. Mai

Digging a new tunnel immediately underneath an old tunnel is going to introduce different stresses on the old tunnel So then dig the new tunnel beside it. Maintaining access to existing infrastructure during construction is complex after all. For many complex industries, there is innovation and cost reduction. Digging larger parallel tunnels is something that the industry should be making easier and cheaper, leveraging the existing infrastructure. The mindset that "tunneling is expensive" is exactly the kind of self-fulfilling prophecy which prevents such progress.

jcranmer 8y ago
> So then dig the new tunnel beside it. What if there are things in the way? Like... building foundations. Stations. Access to the first tunnel. Lots of stuff that might be reasonably expected to grow up in close proximity to a tunnel. Digging two tunnels at once is going to be much cheaper and easier than digging one tunnel and then digging the second tunnel much later, especially if you never planned to dig the second tunnel.
- stcredzero 8y ago
  What if there are things in the way? Like... building foundations. Then dig deeper. Given the strategies talked about by Elon Musk, the original Boring Company tunnel would have been dug to avoid those in the first place. Stations. Access to the first tunnel. Those wouldn't have right of way problems. Digging two tunnels at once is going to be much cheaper and easier than digging one tunnel and then digging the second tunnel much later, especially if you never planned to dig the second tunnel. Therefore, the logic is to dig everything you might imagine you might need, ever. Therefore tunnels are always going to be super expensive and elaborate.
  - jcranmer 8y ago
    > Therefore, the logic is to dig everything you might imagine you might need, ever. Therefore tunnels are always going to be super expensive and elaborate. Not everything you might imagine you might need, ever. But everything you can reasonably forecast to need in the next 50 years. The thing about tunnels: tunnels aren't expensive, stations are (particularly the station mezzanines and the pedestrian circulation to reach them). A two-track subway line is only going to be ~30% more expensive than a one-track line, and a four-track line only ~50-60% more than a two-track line. And it doesn't take a genius to figure out which one you need: one-track lines are never a good idea, and four-track lines are only necessary for trunks in megacities. You can look at your demand and figure out if you're going to need to go to 8- or 10-car trains as your maximum train length. Not to mention that you also (as a city) have the ability to steer development to increase demand on your subway networks via tools like zoning. Insisting that you have to build only to minimal, current demand scenarios is being penny-wise and pound-foolish.

jcranmer 8y ago

> So then dig the new tunnel beside it. What if there are things in the way? Like... building foundations. Stations. Access to the first tunnel. Lots of stuff that might be reasonably expected to grow up in close proximity to a tunnel. Digging two tunnels at once is going to be much cheaper and easier than digging one tunnel and then digging the second tunnel much later, especially if you never planned to dig the second tunnel.

stcredzero 8y ago
What if there are things in the way? Like... building foundations. Then dig deeper. Given the strategies talked about by Elon Musk, the original Boring Company tunnel would have been dug to avoid those in the first place. Stations. Access to the first tunnel. Those wouldn't have right of way problems. Digging two tunnels at once is going to be much cheaper and easier than digging one tunnel and then digging the second tunnel much later, especially if you never planned to dig the second tunnel. Therefore, the logic is to dig everything you might imagine you might need, ever. Therefore tunnels are always going to be super expensive and elaborate.
- jcranmer 8y ago
  > Therefore, the logic is to dig everything you might imagine you might need, ever. Therefore tunnels are always going to be super expensive and elaborate. Not everything you might imagine you might need, ever. But everything you can reasonably forecast to need in the next 50 years. The thing about tunnels: tunnels aren't expensive, stations are (particularly the station mezzanines and the pedestrian circulation to reach them). A two-track subway line is only going to be ~30% more expensive than a one-track line, and a four-track line only ~50-60% more than a two-track line. And it doesn't take a genius to figure out which one you need: one-track lines are never a good idea, and four-track lines are only necessary for trunks in megacities. You can look at your demand and figure out if you're going to need to go to 8- or 10-car trains as your maximum train length. Not to mention that you also (as a city) have the ability to steer development to increase demand on your subway networks via tools like zoning. Insisting that you have to build only to minimal, current demand scenarios is being penny-wise and pound-foolish.