The Scenario: Holes, for footers, have been dug out with an auger to a depth of about 48 inches. The bottoms have been flared out an extra few inches. A few inches of crush stone was added and concrete was poured. Just before the holes were filled, a ~24 inch section of round form tube was added to dress up the top of the footer. The top of the tubes are about 2 or 3 inches above grade.
The Question: If the auger used was the same diameter as the form tube going into it, how does one backfill around the tube? Obviously, there's little or no room for dirt to get between the outside of the form tube and the earth. I've seen conflicting info. Some say to use the auger to make the hole, drop the tube in and fill. Others say to dig the hole bigger and backfill as you fill. At this point, the holes are poured so I hope I'm not screwed.
Some say that the small irregularities between the soil and concrete where there is no tube allows/enables/exacerbates frost jacking. My dad use to backfill the small space with sand. It pours in reasonably well is less likely to hold water. Tamp down every foot or so.
Dirt around it will settle around the pier but i think it's better if you can fill now and tamp as best possible so water doesn't channel into it. Rebar, maybe half to one inch black pipe with a cap that you can pound with a 5lb hammer, any thin enough bar. Dig out around the pier and try to fill and tamp from the bottom. Do this evenly so you don't tilt the pier by too much force from just one side. This is esp true if the piers are close to the foundation. You don't want any water to find a channel near the foundation unless you're controlling it.
In nj and frost depth is 36". I dig a bit deeper, do a flare like you did, but use full 36" or bit more tube. The way you did probably is fine. Before the tube, most of the piers were poured into the hole. This can make frost heave worse but, historically, not that many failures. I don't think i read any such post here, example.
Copy all! I know I had some fine sandy soil I was trying to get down between the tube and the earth. I also know we had some rain recently. I figured the rain would have rinsed it further down and compacted it a bit. I'll try to tamp it with something thin; I doubt a 2x4 will fit down there now as there's hardly enough room for the sandy soil to work its way down through the gap. I'd like to think I could have a go with it pretty well since there's only 20" of tube/soil I need to tamp. In my mind, it shouldn't move too much with that large plug at the bottom. I do have one hole that ended up a little on the larger side so I used a full tube. That one, I'll need to be careful with. I can see how it might want to teeder inside the hole. I'll need to figure out how to effectively tamp it all the way down.
I'll tell you what; it's a mixed bag out there. Some holes, I can get the digging bar pretty far down. Others, it seems like I can't even break through the clay that has hardened around the top of the tube. We had issues with this layer of clay... I think they brought in a load of junk fill-dirt when they built the place. The native soil several feet down is a dream with work with! The standard tow-behind post-hole-digger didn't put a dent in the top layer. Had to get a dingo in here and I still had to fight (5-10 minutes in most cases) with getting through the top layer. This brings me to another question. With me working so hard to pack the soil around the tubes, I worry that I'll be poking holes more than packing soil. What's the chances of this action doing more harm than good? Should I just poke the holes like I'm doing with the digging bar and then fill them with sand as was mentioned in a previous post?
As near as I can tell, the sandy soil we funneled down between the earth and tubes has worked well. I'm only able to easily break through the top inch or two. It looks like it has filled the voids below. I kept poking at them for several minutes and never got much further so I'm guessing they're in pretty good shape. I do have a few that need some attention....
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