I have been searching for this answer for a long time and I haven't found any info on the way severed lines are repaired. There must be tens of thousands of tiny wires that must reconnected, and in the proper order, before the line can be put back into service. What tool and technique is required to achieve such a daunting repair?
A cable for POTS (Plain Old Telephone System) service may have up to 200 or 250 pairs, if I recall correctly. The pairs are all colour-coded, with 25 different colour combinations, then a bundle of 25 pairs are wrapped with a coloured tape, and several bundles, each with a different colour tape, are used to build a large cable. (numbers may be wrong - it's a long time since I worked for a Telco)
I recall seeing technicians camped out in tents on the phone lines doing the splicing - haven't seen that for many years.
The answer is, sadly, just as daunting as it sounds. I've been involved in a few 500+ count fiber optics slicing repairs. It can take a team of workers several hours to complete.
Each wire (or optical fiber) needs to be identified, prepped, and spliced individually. Each wire is color coded and organized into further color coded bundles within the cable. Each bundle is organized in a tray within a splice enclosure (example below).
It's been a long while since I've been in the game, but at the time we were using "Scotchlok" gel filled pinch splices for copper and fusion splices for fiber.
Looks like copper splicing has come a long way, or I was just doing it the hard way before. Options exist (video) to simultaneously splice an entire bundle at once. Colored pairs still need to be organized and routed individually, but it may not be necessary to perform each physical splice individually. Fiber still seems to be a one or two at a time project though.