Now that's an interesting idea. Dig a ring of small holes around the perimeter of the tunnel and use them to build the tunnel liner. Then remove the dirt and rock in the middle.<p>Microtunneling has been around for years. It's done with small tunnel boring machines, to install pipes of various sizes.[1] The drives are usually not that long, because these are pushed from the starting point, not self-propelled like the big TBMs.<p>That's what they seem to be doing here. There's some hand-waving around the "special borepipes". Those are apparently drilled by existing techniques. Only when all those tubes are in place around the perimeter of the tunnel volume do the robots move in and grout.
Trying to do all that pumped concrete grouting work with those small tubular robot vehicles is a neat trick. The animations show them drilling small crosswise holes longer than the tube diameter, which is a bit suspicious.<p>All this would seem to be limited by how far you can drive the "special borepipes" using standard drilling techniques. That can be quite a distance, though; the current microtunneling record is 2.2 km.[2] That's more than enough for most urban projects. You're going to want stations and access points along the route, so the drive can be done in sections.<p>(When watching the original post video, start at 3:30 to skip a long ad.)<p>[1] <a href="https://www.youtube.com/watch?v=teVrJs6CSe0">https://www.youtube.com/watch?v=teVrJs6CSe0</a><p>[2] <a href="https://www.napipelines.com/building-big-microtunneling-terratest-world-record-project/" rel="nofollow">https://www.napipelines.com/building-big-microtunneling-terr...</a>
The content about the new method starts roughly here: <a href="https://youtu.be/bfJY0syocfU?t=227" rel="nofollow">https://youtu.be/bfJY0syocfU?t=227</a>
This is definitely an interesting take on tunnelling, but I struggle a little bit to see how this would be either faster or cheaper than conventional methods.<p>First off you have to buy a load of strong and mechanically complicated robots (expensive), and then many small tunnels to put them in. Drilling these small tunnels won't be that much faster, and certainly no cheaper than one big one, assuming they're using conventional microtunneling equipment (required for the accuracy).<p>Also, what happens if a robot breaks down mid operation? Are you going to go fishing, or try and send in a human to dig it out? Worst case, you can't do anything and have to revert back to manual digging the whole way. You really don't want a timeline to blow up like that in a real project!<p>This system has the big advantage that everything is modular, so a bigger tunnel just requires more robot mini-tunnels. Economies of scale should make everything a bit cheaper, especially since the robots and mini-TBMs would be reusable.<p>Getting geology before you tunnel is also a benefit, but if this was so good, surely tunneling contractors would already do this by sending just one micro-TBM ahead of their main one! What can this system actually do if bad geology is detected? Not much...<p>Fundamentally the robots don't really solve anything except overcomplicating tunneling. You still have pretty much all the expensive parts (materials, spoil removal, planning, investigatory drilling, sinking shafts, etc) but now with the additional costs and uncertainty of having loads of robots too.<p>If you asked me to design a lining-first tunneling method, I'd completely ignore robots and try and use existing technology first. Take horizontal directional drilling equipment, make it cheaper and just directionally drill a ring of wells. Pierce the casing at a regular interval, and then fill the whole thing with high pressure grout. No robots needed and this happens everyday, just vertically rather than horizontally.
So the robots are building the shell of the tunnel before the material within the tunnel (spoil) is removed.<p>The robots do not seem specifically involved with removing spoil or even carving it into smaller pieces (at least pieces smaller than the tunnel diameter).<p>Does this mean building tunnel shells is the hardest part of tunnel building, not breaking up and removing spoil?<p>Or does this approach somehow make it easier to fragment and remove the spoil since it's now in tunnel-sized chunks?<p>(Edit: Yes, stabilising the tunnel is the hard part, see excellent and thorough answer by rmccue)
I'm not a construction engineer by any means but there are a few things I can't warp my head around. Why are they using robots at all? It seems like a pretty big hassle to construct those robots that deposit large amounts of material with high pressure through a hole that needs to be drilled in their own tunnel.
Why not excavate the volume between the small boring holes with the same technique they used to create them in the first place? Bore those smaller holes with equal spacing, fill them with concrete, and then repeat for the volume in between.
What about steel? Not needed for in tunnels?
Seems like a cool concept but also quite early stage with unsure viability. Curious how transportation would change if they succeed in making tunnels x2 cheaper.
I figured the Boring company had a similar approach, but when I researched their technique ... I was very disappointed. This is really cool. Can't wait to see it go into production.
While this method can create new tunnels, I see it’s first best use at enlarging existing tunnels by setting the “concrete” type stuff surrounding an existing tunnel but at a larger diameter (well, also need not be round!). Then demolition of the existing tunnel walls and some cave in of other materials and you have a new larger tunnel after cleanup.
@6m Could build tunnels up to 10 times faster and at half the cost.<p>A lot of US cities could be retrofitted with subways.<p>Even NYC metro area badly needs a few more tunnels:<p><a href="https://en.m.wikipedia.org/wiki/Gateway_Program_(Northeast_Corridor)" rel="nofollow">https://en.m.wikipedia.org/wiki/Gateway_Program_(Northeast_C...</a>
Seems to be missing a first set of robots that digs the pipes, heck creates the pipes, for the second set that creates the tunnel, before the third set clears the hole. Whew, that is a lot of bots.