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I am trying to dig holes that are 18" square, and 12"+ deep.

The site is mostly undisturbed soil, although there is a thin layer of topsoil or fill in some areas. The soil is glacial till, so a mix of sizes. Plenty of rocks.

I use a mattock to loosen the ground, then a shovel to, err, shovel it out and clean up the sides. I have trouble when I get close to the 12" mark, because I can no longer swing the mattock into the hole. If I need to go deeper (because I hit soft fill dirt) then I'm kinda stuck.

It's also taking a while, and I have 30 holes to dig, so I'd like to think about ways to speed things up.

For context: I'm going to fill with gravel and set pre-cast pier blocks on top.

Any suggestions?

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You could call your local landscaper, they should have a small backhoe that can come out and dig the holes in no time. They probably even have one with an 18" bucket, so it will take them longer to move from hole to hole then it will to dig the hole. This option might be out of the budget, but it could save on visits to the chiropractor. –  Tester101 Feb 15 '11 at 12:51
    
@Tester101 I imagine an excavator making a longer hole than I want, which will mean more filling later. Am I wrong? –  Jay Bazuzi Feb 16 '11 at 1:32
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I often rent a small Kabota with a tiny backhoe or post hole auger. It costs me about $100 a day, but makes the work fast and easy. Adding a little bit of extra back fill is a small task compared to digging by hand. If you put the spoils on a small plastic tarp next to the hole, your back fill is right there waiting. After your blocks are in place and back filled, simply drag the extra spoils away to your disposal area. Makes clean-up around your new pads much easier. –  shirlock homes Feb 16 '11 at 11:04
    
Be careful of an auger if there are rocks - it can catch and jamb or not work if the rocks will not go through it (too big of rocks) BE SAFE –  Mark Schultheiss Feb 18 '11 at 0:02
    
FYI, I rented a gas-powered 2-person auger with the largest drill they had, 12" diameter. It worked really well except when it hit a rock it couldn't move, and it struggled with roots a bit. But now I still have a lot of hand digging to finish the holes. They also had a Toro Dingo with a 24" auger; I may rent that and re-drill the holes. –  Jay Bazuzi Feb 22 '11 at 6:52
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2 Answers 2

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For that size hole, I'd probably go with a Post Hole Digger. If it's sharp and there aren't too many rocks or roots, you just shove it into the ground, pull the handles apart, and lift.

However, for the number you're going to be digging, it might be better to visit your local tool rental shop, and rent a gas powered auger. If you can get a second person, the two person models are a lot easier to control ... you can then square it off with a shovel, and either get the last bit out by hand, or with a post hole digger.

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Thanks for your answer. For this soil there are too many rocks for a post holer. For the gas auger, I worry that with all the work of squaring, cleaning out the hole, and shoveling away the spoils, that I won't save much. Maybe I'll give one a try, though. –  Jay Bazuzi Feb 15 '11 at 2:45
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@Jay : well, if that's the case, and it's just a matter of loosening up the rocks, you might see the hardware stores near you carry "digging bars" (might also be called a "San Angelo Bar", "tamping bar" depending on the exact style or just "pry bar" ... basically, it's a long (about 6') thick (about an inch) steel bar, used for loosening up rocks in the soil before you dig. Some are more pointed, some are more like a blade ... you drop it into the hole, wiggle it some to loosen the soil, repeat a few times, then extract with the post hole digger. –  Joe Feb 15 '11 at 4:45
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I tried a digging bar today. We hit a few really big rocks and it was perfect for prying them out. It also works well for loosening the bottom of the hole where the mattock can't reach. –  Jay Bazuzi Feb 16 '11 at 1:30
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Of course, if you don't mind spending money, an auger is the best way to go. Another option is the Garden Claw, but I have no idea if it actually works.

Sadly, the best "free" solution I could come up with is using a 2" auger bit (as opposed to spade, etc. bits) in a cordless drill... which should go ok if you clear the bit often. You could also repeatedly slam a piece of rebar into the holes, but that sounds extremely tiring.

If you're going for "comic relief," I would suggest a pogo stick with some metal stakes welded onto the end.

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Garden Claw!!! 2" Auger Bit!!! The OP wants a solution to speed things up, not slow them down! You should add table spoon to the list ;p –  Tester101 Feb 15 '11 at 12:46
    
If the ground is hard, it'll help. Large earth augers are obviously the best solution, but you aren't going to get that type of performance from anything free that is readily available in most garages. Bottom line is that if you either spend money, making it easy, or you do it for free and work harder. –  Michael Feb 15 '11 at 17:39
    
I'd add the Garden Claw and 2" auger bit on a cordless drill to the "comic relief" category. The Garden Claw will NOT help. I own one and it's back-breaking work just to loosen up compacted topsoil only 4" deep. Even worse, my Garden Claw's tines bent! Breaking up 324 sq. in., 3.14 sq. in. at a time with a 2" auger bit would be even slower than just jamming a shovel or post hole digger into the ground to break it up. –  rob May 6 at 18:00
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