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Boring Company

Buckminster

Well-Known Member
Aug 29, 2018
5,167
27,815
UK
The question regarding spiral welding Super Heavy was raised by KarenRei at the beginning of the year. Twitter

He mentions in that tweet that the hyperloop is spiral welded. That one was made in free space which is easier

For a positive pressure tunnel, they will still need to pump slurry to the front to seal and fill the tunnel to excavation gap. Pumping is easier than solid segments though.

Elon mentions reinforcement which may relate to the rebar in the segments versus the tunnel itself.
If he is talking rebar, that is also interesting. Feeding and bending rebar is much simpler that sheet stock. Concrete pipe uses a similar technique with rebar on the long axis and rewire spiral welded along the length.

In this setup, they could feed the rebar, bend into shape, then cast the whole thing in place. It might make the most sense to do the inner tunnel seperate from the slurry fill due to material requirements and access. I'm not sure if the cure tine and process control lines up with tunneling speed goals. However, by gripping more cured segments further down the tunnel, they can trade mechanics for cure time.

Continuous spiral welding of a tube in place is possible with the difficulty dependent on thickness and width. (Bend radius/ feed angle/ uncoiling). Curves would requires shaving or corrugating if doing edge welding. If doing overlap (telescoping) then that is easier. The shield can provide a gap for access to the back side of the weld. SpaceX uses friction stir welding which might be an option and works well with overlap.

Possible hybrid approach is steel sections. The sections could be one piece of tunnel diameter size sent down the tunnel with the ends overlapping (so as to fit). The piece would then be threaded around the TBM push rods which engage with features on the previous segment. Once in place, the piece is expanded and welded to itself and the previous section. With these, they can pre cut the segments with a taper. That taper allows the tunnel to curve based on rotational orientation similar to HVAC ducting.

They could feed and cut these sections in place. That eliminate the issue of rotating the feed material around the circumference since they can pull one or two wraps off at a time with a free end, versus a captive end and moving the coil.

Steel tunnels of various designs are used in immersesed environments:
https://www.sciencedirect.com/topics/engineering/concrete-tunnel
Check out the Bai Yun paper.

The outer concrete slurry would provide protection, and they can add a protective coating while the steel is still inside the shield.

(Grain of salt, not a tunnel engineer)

I love following Elon how so many reasons. Understanding tech like this is just one. Surely the holy grail is:
  • No overlap
  • Curves are surely easy enough given the relative scale
  • Zero inspection / removal of weld material
  • Pump concrete ~1 foot behind weld
  • Weld brackets directly
  • Reduction in cost of TBM by removing the concrete sections should be so significant that the speed becomes less important
 
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mongo

Well-Known Member
May 3, 2017
16,652
62,732
Michigan
I love following Elon how so many reasons. Understanding tech like this is just one. Surely the holy grail is:
  • No overlap
  • Curves are surely easy enough given the relative scale
  • Zero inspection / removal of weld material
  • Pump concrete ~1 foot behind weld
  • Weld brackets directly
  • Reduction in cost of TBM by removing the concrete sections should be so significant that the speed becomes less important
Yeah, he and the team come up with some cool solutions.

If they don't overlap, the only way to curve is to cut, stretch, or gap the section. Depending on the material width, gap adjustment limits the curve radius. Same sort of thing as bending tubing, it likes to buckle.

The shield is large to begin with, at least one concrete segment section for normal TBM, two sections for place while digging ones. Overlaping weld might make sealing it a little trickier, but that could be within the variance it already deals with.

Upsides are:
Better sealing, no need for adhesives.
Eliminating the area needed for section casting.
More use of lower strength concrete for grout. Allows reuse of tailings.
Potentially larger interior diameter for the same hole size.


Potential issues:
Cross drilling for on/off ramps or service tunnels.
 
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Just watched recent Elon presentation on Boring Company. I'm actually most interested in use for cars which wasn't discussed much.
I like the concept of self driving cars navigating between white lines. Top speeds would probably be less than 100mph? Adding a tail wind artificially would of course help immensely. Otherwise cars might be loaded on some kind of railcar?
Precise location of vehicles would be crucial assuming multiple cars in tube at once. Unless tight follow scenario used to minimize air drag is used? Vehicles would leave in groups then. Current Tesla's could be programmed with this feature easily.
I'm pretty confident these tubes won't be for running ICE cars. Great complement to further promote EVs?
Sounds like they will be focusing on pedestrian transport first however. Very excited to see how this technology evolves!!
 
So is The Great Pyramid of Giza = The Egyptian Pantheon? Trying to figure out why Elon said "The Egyptian Pantheon", as I'm not familiar with that name/structure; but I'm not an Egyptian scholar.
You can't find it because there is no such thing. Elon was trying to come up with off-the-cuff references to classical structures and simply conflated The Pantheon in Rome with Egypt.
BTW, The Pantheon was so well engineered and the quality of its concrete so good, that it still stands in excellent condition after almost 2000 years. By contrast, modern reinforced concrete structures crumble away in a century or so.
 
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Reactions: skitown

mongo

Well-Known Member
May 3, 2017
16,652
62,732
Michigan
As discussed by Will here, key improvement is ability to start boring from the surface. This is not easy but comes with many benefits. Cost, removal of muck from surface, time etc.
I think Will is reading too much into that photo. You can see the lift points are still attached to the machine meaning it is not actually going to be sent underground at that point. Further, the machine is missing all the other sections it needs to operate. I think that is just a test setup for the digging head.

Intermediate nodes would still be vertical shafts. The Vegas drill and fill concrete side columns allows for quick setup of start/ end holes. The muck removal can still be done using gantry cranes at access points and the level tunnel reduces the power the muck carts require.

Not to say they couldn't slant launch it, but that results in a lot of shallow depth tunnel that needs to be clear of obstacles.
 
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RubberToe

Supporting the greater good
Jun 28, 2012
3,373
8,817
El Lay
Somewhat OT but transportation related...

One of the companies working on the German Gigafactory is a large German conglomerate called Max Bogl. I happen to have a web page open where the company was mentioned concerning a delivery of a new kind of urban maglev to a Chinese city for a demonstration project:

Maglev flies from Germany to China

Haven't been hearing much about Maglev recently. Apparently the difference with this new approach is that it is much lighter, slower (90mph max), easier to construct, and most of all much cheaper than say the German Transrapid. Better turning radius, and uses modular track sections tha can be built in a factory and shipped to the construction site:

TSB demonstration line in China - Max Bögl

Couple videos of a test track and a discussion with the developer shown here:



These kinds of systems work great but obviously don't have nearly the flexibility of a TBC system. The more I look at the way that the Vegas system is being implemented, the more I like it. Especially when you can put a station above ground literally right next to a casino entrance, then have the "pod" on tires navigate through a parking lot a short distance to where the tunnel dives underground to separate from the local traffic. Then you end up right where you want to be on the destination end. I could see every casino in Vegas having a TBC station. If they can get the tunneling cost down to a reasonable level, seems like thats the key.
 
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