See how far various soil types spread when dumped
Description of my soil test
Test Results
Screenshots
Conclusion
We could use this knowledge to create a “wall” of rock or slag before dumping waste in the ocean.
I also noticed that when digging the results are very similar. It’s harder to test this because when digging you can’t guarantee to get a single type of soil. For example, when digging into Coal/Iron/Copper we usually get some dirt/rock/gravel, and there could be a top level of dirt as well. So results may vary.
However, if the soil is mostly Coal/Iron/Copper or even Rock, I may not bother with retaining wall as using them (especially staggered every 5 levels) will result in taking much more space.
Thanks to Undying29 for his great guide, all credit goes to his effort. you can also read the original guide from Steam Community. enjoy the game.