Sorry, couldn't help the subject line. [img]/forums/images/icons/grin.gif[/img] I just had to do it.
Anyway, what I'm really interested in is anyone's experience trying to dig multiple holes close together to make one big hole. I'm in the market for a PHD. For the most part, what I need it for is to set fence posts, and a standard unit with a 9" auger will do the job just fine. But I also have two pole buildings to do (probably about 25-30 poles total) that need bigger holes. The books I've read want me to put in 36" diameter holes, but they are thinking about houses and stuff, not a single story shell building like I'm going to be doing. So...what seems to be the trick would be to put three 9" holes close together in a triangle and end up with effectively about an 18" hole. It would seem, in theory, that I could jam some 4x4s or something in the first hole(s) to keep them from caving in when I dig the second and third ones. But, as we all know, sometimes theory works great till you try to really do it. Anyone ever tried such a scheme? Or alternatively, does experience say that for light shell buildings (no floor, metal roof) a 9" or 12" hole is sufficient? I'm in VA, so the ground is mostly clay (unfortunately, the bottom of the list when it comes to its ability to support weight). Yea, I know, just buy a HD PHD with an 18" auger and quit worrying about it. And that is a great answer...if you're loaning your checkbook.
It won't work. The digger will just move to the side into the other hole. It will be a mess at best and dangerous at worst. Whatever you do don't put a post in the hold you already dug. If the digger catches that again at best it will destroy your phd and at worst it's going to fling the post out of the hole and kill somebody. A 12" auger won't be much money and then you can just dig out a little. I can't for the life of me think of why they would want a 36" hole. They don't even do that to put in telephone poles. With a 12" hole you will need to dig the bottom out a bit to either put in a concrete block for the posts to sit or just fill the bottom of the hole with 6" of concrete and forget digging them out. With a pole building your posts are probably only going to be 6x6's anyway.
The multiple hole thought wont work. The auger will find its way into your first hole. Maybe just maybe if you stay far enough away from the first hole it might work. One deflection from a rock or root and that auger will take the path of least resistance. 36" hole seems way out of line. Ive drilled holes for decks and small barns with my 9" auger and all was to code in Upstate NY. And they are picky here. The nice thing with a bigger diameter hole is its easier to get your post lined up to each other. Ive had real good luck keeping things square with my 9" holes. Anyone ive ever drill for i just tell them you make the "X" Ill drill the hole [img]/forums/images/icons/smirk.gif[/img] Never had a problem yet [img]/forums/images/icons/cool.gif[/img]
If you don't want to buy a second auger, and they're only about $100, you can use a handheld posthole digger to open up your hole after you drill the hole. I did this last summer when I added on to my barn and it wasn't a lot of work. Depending upon your soil type its a good idea to make your hole big enough so that you can put at least a 12X12 pad at the bottom of each hole to set your posts on.
Are you sure the 36" is diameter and not depth? A hole that diameter would provide for one huge anchor, but I'm not sure it would be a great advantage over a smaller anchor. What is your soil like?
Yea, the books that I've read about pole buildings really are calling for 36" diameter holes (for clay type soil). But they are talking about building pole homes and stuff, so the weight load on each pole is significantly more. The books I've gotten on horse barns and outbuildings kinda gloss over the details. They talk about optins like setting the poles on a concrete pad, but fail to discuss little nuances like "what size pad."
Cowboydoc, your insight about what happens if the auger catches some wood jammed into the first hole(s) is a good point. Makes a strong argument for buying the bigger equipment. Collective knowledge is a wonderful thing!
From my research, it looks like I can purchase a HD PHD with an 18" auger for about $350 more than the lighter weight one with a 9". Seems like a lot of extra money at first, but in the long term price of two buildings it kinda gets lost in the rounding. And it will also make planting trees and bushes a lot easier. I don't know about the rest of you, but as the years have added up, I'm finding that the cost of the tree is less of an issue, whereas the aches and pains from digging the hole.... [img]/forums/images/icons/frown.gif[/img]
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the books that I've read about pole buildings really are calling for 36" diameter holes (for clay type soil).
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When I build my pole barn, I recall my research saying that the important thing was the surface area of the pole in contact with the surrounding soil determined the pole's loadbearing capacity. In other words, a smaller diameter pole, set deeper had the same load bearing capacity as a shallow-set large-diameter pole.
Further, the effective diameter of the pole could be increased by encasing it, and attaching it (e.g. with lag screws poking out of the pole) to a concrete collar. Unless you're going to fill the 36" diameter holes with a concrete collar, I can't see how the size of the hole is going to increase the load bearing capacity of the pole.
At the risk of getting this post deleted, I'll summarize...
It's the size of the pole not the size of the hole. [img]/forums/images/icons/blush.gif[/img]
Setting the pole on a concrete pad may increase weight bearing capacity but a pole's embedment also needs to resist upward loads and a pad does nothing for loads in the upward direction.
Just what I recall from the books I used as reference.
Perhaps you fellows are getting caught in the realm of piles. When you do this soil data is analised by engineers and the appropiate pile designed.
The pile may be a friction type concrete poured in place, a metal or wood type driven to refusal or perhaps an end bearing type requiring a large, usually concrete, base to support the weight. These are called end bearing piles with the base being much larger than the supporting pile. When drilled there is a bell tool atachment that is used to increase the diameter of the pile footing.
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