This isn't super difficult, but also not super easy.
After reaching the moon (at debth 1000) I felt like I hit a barrier. The next expansions were very expensive and the drill was very slow. So I decided to work on this achievement and the one for 1,000 construction equipment as well.
It helps to have the right relics:
1. First priority is to get those Relic Bags to increase your max number of relics from 10 to 15, they appear at random from scientist excavations
2. Whenever you have the chance to get Book of Secret you should try to get it, they appear at random from scientist excavations
3. it helps to have some books of success, I had 55% increased success rate as a reference
4. The rest of the slots I had filled up with cave improving relics only: Fuel Extractor, Fuel Tank and Rocket Booster
I had used Book of Secret on both Book of Success and cave relics. After this achievement you can replace most (or all) of the cave relics with other relics that fit your current need.
For the caves itself:
1. send in magnet drone to the very end to clear the main path of rocks and see where stuff is
2. use 1 - 2 regular drones to the very end to collect stuff from the main path and as much from the very end as possible
3. use flying drones for closer & isolated stuff
The worst part is babysitting the cave for the complete time (>1 hour each). And not get distracted by somethign else.