Salem

How much dirt can I dig/move?

Could I pile dirt into huge hills and earth mounds?

Could I dig huge dirt walls to protect my settlement?

I'd experiment and find out for myself if it wasn't such a tedious thing to do.

10 Units of Dirt is the maximum you can hold, until you learn "Laboring", which ups that to 15.

You make mounds of dirt, but there is a slope height limit of 10 units. It is not possible to create artificial cliffs.

A Dirt wall can look cool, but won't do anything for you defense-wise. Also, Walls complain if you try to build them next to steep slopes.

A Metal Shovel is a truly great tool, but you can also improve your digging ability by slotting artifacts into your clothing. Every "Enforced Seam" increases your dig-progress by +2% per time unit, and each Feathered Brooch gives you +1%.

More information can be found on the wiki article: http://salemwiki.info/index.php/Dig