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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):

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Mini skid-steer (Dingo) with auger attachment (up to 16" auger + extensions):

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Mini-backhoe which claims 6' digging depth:

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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.

  • So, the soil is the same all the way down to depth? Any large rocks? That info will make a difference. – Solar Mike Apr 16 at 9:38
  • @SolarMike thanks, I have added an update. It seems to be consistent based on past work. We've seen very few large rocks but smaller ones are numerous. – DaveInCaz Apr 16 at 9:44
  • Have you considered using helical piles instead of digging? – Matthew Apr 16 at 13:48
  • @Matthew yes and I am actually awaiting a quote for that. The anecdotal costs I've read about seem reasonable. Getting contractors to actually quote for things around here however is quite hard sometimes. – DaveInCaz Apr 16 at 14:00
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    +1 for the dingo, 20 holes is a chore. let the hydraulics of the dingo do the lifting. And Dingo was its name-o! – Alaska Man Apr 16 at 17:01
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Having dug footings before by hand (2-man auger, clamshell digger and shovel) I would definitely suggest the Dingo for this project. I did 5 with the auger and 2 with clamshell (because it was near utility lines) but 20 footings is a lot and you should keep this simple and quick, letting the machine do most of the work.

Note- clamshell post-hole digger example:

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A clamshell is not better than 2-man auger, it's a lot more work but you have to hand dig near utility lines. The 2-man auger has 4 handles and the motor in the middle, one man operates from one side and the other stabilizes as it digs. It's fast but it's a lot of exertion, especially for as many footings as you're talking about.

  • Thanks for clarifying, I understand now. The auger I'm considering is like a trailer, much bigger than a 2-man auger. But I don't know how it would compare to the Dingo. I agree a clamshell would be a huge PITA! :) (now that I know the term for it!) – DaveInCaz Apr 16 at 13:13

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