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.