https://en.wikipedia.org/wiki/Directional_boring
You've probably seen them on the side of the road, looks something like a big skid steer with a stack of pipes on the side. It's much more practical to put a person running a piece of construction equipment on the surface than trying to miniaturize and automate a TBM.
To use the equipment, a mini-excavator digs two small holes for the entrance and exit 20 to 200 yards apart, the HDD rig is rolled up, and a 10 foot length of 2" pilot boring drill rod is pushed in. The HDD rig connects this to the next pipe in the stack, and is able to rotate (with extreme torque), push (with limited force), pull (with extreme force), and pump fluid through the drill rod. A locator walks around with a receiver that can measure the position of the tip of the drill underground. On smaller installations, the tip of the pilot drill is slanted, and to go "straight" you need to continuously rotate the drill, or you can bias your pushing and turning to move with the slanted tip aimed in one direction and go up, down, or sideways. Bigger ones have downhole motors and steering tools that can use hydraulic pressure from the mud being pumped through the pipe to cut harder soils or go farther with less friction.
When your pipe is pushed through and comes out the exit hole, you attach a back-reamer to the drill head, and pull it backwards to enlarge the hole (pulling additional drill rod, installed at the exit pit, behind it). Finally, attach the conduit, fiber, water or gas pipe, or whatever you're installing and pull it all through. Then you make your exit hole an entrance hole, fill in the original, and install a junction box to connect the two segments.
It's simple, cheap, effective, and proven technology for utility-level scale - there's probably one of these working somewhere within 10 miles of you right now. Unfortunately, it doesn't scale up to TBM size.
Cut-and-cover[1] construction is an order of magnitude cheaper. You don't need TBMs unless you're going really deep, or there are things on the surface that are really expensive or disruptive to work around.
That maintenance is needed because of how much material has to be cut, not by how long it's sitting there, so going faster means going through more material and wearing down the tools faster. You'd have the same total amount of time spent maintaining it (assuming going faster doesn't wear the tools down even faster, which is iffy). So just digging faster runs into Amdahl's law; you speed up a portion of the process but the total gains are less because the other parts are fixed.
(And, as others have said, yes there's a faster way; cut and cover.)
Yes, a lot, but not all:
> In December, the TTC bought a banner ad on the Tunnels & Tunneling International website, to list for sale four tunnel-boring machines it used to dig the 13.5-kilometre twin tunnels for the Spadina subway extension to York Region. The TTC had bought the machines in 2009 from Lovat for $58-million. Today the TTC has stored the machines at the Keele Valley landfill site. The machines are nearly good as new, the TTC says. “The TBMs are generally considered to have a useful life of tunneling of approximately 20 kilometres,” reads a TTC tender document. “At the completion of this project, they would have been used between 2.5 and 3.2 kilometres, or approximately 10-15% of their useful life. Accordingly, the TBMs will be capable of significant additional tunneling on other projects.”
* https://nationalpost.com/news/toronto/why-metrolinx-plans-to...
If you want to excavate a rectangular tunnel, you want a roadheader.
It's really surprising to me that in 2019 the limiting factor in a billion/trillion dollars industry like transit is something that could be solved with a better conveyer belt.
To ask OP's question another way: many areas of technology and engineering have improved rapidly over the last decade or three. Have TBMs been keeping up?
You sound like Elon Musk. "This problem seems easy. Clearly all existing TBMs suck so we'll just build a better TBM!"
Slow is not a problem. A few meters a day sounds slow, but if you are going long distances you can scale by buying more TBNs putting them in a line and having each meet up to the next. Assuming you have the money. In practice the cost to build a tunnel is high enough that you probably can't afford to scale up too much that way.
This would be impractical for most real-world projects. First, digging the access pits to get the TBM in and out are a significant fraction of the project cost - access pits are really expensive, and require a big space, so you don't want to dig more of them than you have to. Second, you're normally digging a tunnel (rather than building on the surface) for a reason: you're going under something. That something might be a body of water, it might be a mountain, or it might be a dense city full of valuable real-estate that you didn't want to disrupt with a cut-and-cover operation. Either way, it's going to be really hard to dig an access pit right in the middle of it.
Of course for mountains and large water bodies you are correct. The English channel left some TBMs in the middle so they could get done faster - at much higher expense.
What I'm picturing from your statement is two TBM drilling towards each other like ---> <----.
Which would require the digging of a third hole where the TBM "drill heads" meet. After every TBM dig, the drill heads are left at the end of the tunnel b/c they are bigger than the new tunnel (as the head digs the tunnel, workers install support structure to prevent a collapse, so the just drilled tunnel is smaller than the being drilled tunnel). A 3rd dig would be required where the two TBM drill heads meet to retrieve them and connect the tunnels. That's a lot of $$$ :/
In most projects it's called a station.
http://www.crossrail.co.uk/construction/tunnelling/meet-our-...
Occasionally you'll have dive sites that are not at/near stations, but not that often.
https://www.sydneymetro.info/station/blues-point-temporary-r...
Sure you can improve the traditional TBM, but are theses improvement are needed?
Most of us here come from the software world, where sure improvement are costly (still less than in the physical world), but they can also target a huge market for a pretty cheap price.
Who actually need it to be 10 times faster? It takes already a pretty long time just to put in place a project, would it matters if you just saved a few months because the tunnel was bored faster? Sure in some situation, 10 times faster could be useful, but would theses situations be ready to pay the cost to develop that? Why not buying 10 TBM instead? That would even be more flexible.
We do. It's called a directional drill. https://www.ditchwitch.com/directional-drills
1. Are any of these TBM considered state of art? I dont see any tech inside those TBM that could not be done 10 years ago other than the cost of the machine. We are entering new Space Race era and yet some fundamental stuff still looks very, should I say "traditional".
2. Why cant we build even bigger TBM? Like Double the current diameter. Or Bigger TBM that are Rectangular rather than Circle.
3. The biggest problem with TBM is that they are slow. Even if we had made them 10 times faster I would still consider them very slow. Surely there could be technology that improve on it?
4. Are there any reason why we dont use TBM for small pipes, ( like for electricity or fibre optics, )