Oh, and just to follow up on @pemerton's post, an answer on digging from a Quora answer:
So that's 4 cubic yards per day, not 10-15 cubic feet per hour. Gygax had no clue about this stuff.
EDIT: having dug out ditches by hand and actually having cubic yards of dirt delivered, 4 cubic yards per day is reasonable.
EDIT 2: D'oh! misread.
On average Two of us can hand dig and load an 8 cubic yard skip in an 8 hour day,
If its clay, then that halves.
If its sand our production doubles.
EDIT: having dug out ditches by hand and actually having cubic yards of dirt delivered, 4 cubic yards per day is reasonable.
EDIT 2: D'oh! misread.