For this achievement you need to dig 50 tiles of land.
A great level for this is the fifth prison, San Poncho, as digging your way out will net you more than half of the requirement and the general lack of guard duty allows you to quickly search for materials by either searching desks or pockets of other inmates.
Note that you can use any digging tool, and you can dig anywhere for it to count (unlike on the xb1 version upon release).
The first prison Center Perks is also a decent place to work on this if you havent made it to San Poncho yet.