I need to put in about 20 concrete footings for several deck-related projects. The footing base should be 12-18" (but see note below). Frost depth in my area requires footings to be 52" below grade (local building official has stated this).
Soil is clay with rocks, mostly 4-5" across (softballs). Based on past septic excavation, this seems to be pretty consistent.
I'm weighing how to best dig holes that deep. Local equipment rental options are:
Towable post-hole digger (up to 16" auger + extensions):
Mini skid-steer (Dingo) with auger attachment (up to 16" auger + extensions):
Mini-backhoe which claims 6' digging depth:
In theory / "on paper" all of these could do the task. But it is hard to assess which will be the most effective at digging holes. By effective I mean:
Will work well in the soil
Dig a reasonably neat hole to requirements
Not take excessive time or labor
The rental cost for all is roughly the same or at least not a enough to be a primary concern.
I have some experience with small 3-point equipment on tractors and feel confident to safely learn & use these machines.
It is an option to do a larger # of smaller footings (meaning, smaller footprint & less load-bearing) if that makes any difference here. Though all things considered I'd think fewer, larger footings would be less overall work.