Underground pipe insertion process - GIF

[desbromilow]

Wonder how they drill the initial hole and how they deal with any rocks in the path?

You need to look up "direction drilling" and see how it's done.
The "cutter head" comes in a couple of designs, one for soil/soft rock, and one for hard rock. Both handle obstacles by either going through it, or backing up, turning/ readjusting course, and going around the obstacle. NOTE: Somewhere I have a picture of an archeology excavation of a skeleton with a comms cable/ gas pipe right through the skull of the buried person... that is a classic case of the drill not registering a significant obstacle, and simply going through it in this case a 6th century AngloSaxon cemetary which was unknown at the time of the cable/ pipe installation.

Once the drill rod gets through the path between the start and end, "reamers" are fitted to widen the hole to the required diameter, and those same reamers can also be used to guide the pipe back along the opened route (done in one operation in sandy soil since the hole may collapse between passes)

As suggested, look up videos on "directional drilling" and they will explain it better than I