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.
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.