What size hole do I need for cementing in 2.4m 120mm pine fence posts into clay soil?

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Depends on frost depth, height, and strength requirements of fence.

We generally drill 8" holes for a 3.5" square post 6" below frost depth or 30" deep in our area. Minimum depth if frost depth is not an issue I would say is 18" for a heavy clay. Deeper is better than wider. This is for fences upwards of 6' high. Higher fences we would probably set a deeper minimum post depth.

If we had a 120mm round, we would probably stick with the 8" diameter hole, but if it was 120mm square, we might up size to 10" diameter to ensure enough concrete around the post for it to stay intact.

If we needed more lateral strength, we would up size the hole diameter if we did not go any deeper.

For holes that layout cannot be adjusted and are not in the center, we enlarge the hole as needed to make sure there is adequate concrete surrounding the...

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If you have clay soil, you know how slow going digging in it can be. Hand digging in rocklike clay can turn a weekend project into a weeklong affair. Don’t fret though, there are some things you can do to soften clay in a few hours before digging post holes for a new fence or pilings for a deck. Before you get started, check if you need to obtain a permit for the project, and call 811 to ensure there aren’t any underground utilities in the area where you plan to dig.

What Makes Clay Soil Hard

Soil is classed based on the average size of particles it is made up of. Clay contains the smallest particle size of all soil types at less than 0.002 millimeters. But it’s not just the small particle size that makes clay so hard to dig, it’s also its thin, flat shape. Thin particles compact together more readily than round particles like sand. Let these compacted particles dry out, and they become even more difficult to loosen and dig.

Water Makes Clay Soil...

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They are great for low lying spots that are constantly or seasonably wet.

An easy(ish) way to make them on the spot is to take a plastic or black rubber type pipe the correct or preferred size and length. I prefer the black rubber type(see below). Cut it lenghtwise with a saw. This creates a an expansion joint for removing the concrete post after curing. Use some clamps (large hose clamps work well) to tighten the joint.
I have a hole in the ground for the pipe to rest in for filling, just deep enough for it to stay standing. Add rebar for strength if desired or if it will be a corner post but don't let your rebar protrude through the bottom of the cement because it will rust up from the bottom. Pour in your cement mix and let harden. To release simply unclamp the hose clamps and slip form off the top (I reccomend letting them cure at least one week before using).

If you are in no rush for posts you can make one a day, only use (buy) one form, and mix small...

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In the end, there's a lot of ways to do this and tons of different preferences.

My end result was using Weathershield 4x4 posts, and a fairly cheap Spruce fence. Originally was going to be Cedar, but at last minute, wife wanted 4' instead of 3' but - oddly - no one locally had 4' in cedar and I knew that the long Labor Day weekend would be my only chance to do this for awhile. So I just got the spruce. After we paint it, maybe it's only good for 8 - 12 years instead of 18 - 20. It was really cheap, (about $35 for 8' panel, which I sliced up as necessary to make gates, etc.) Since we're painting it anyway, I figured Spruce wouldn't be that horrible as compared to cedar in terms of looks. If leaving it natural wood, I'd have waited to get cedar.

Ended up using 6' 4x4's and 2 1/2 foot holes with some tamped gravel in bottom of holes. So 2' of posts are underground with QuickCrete up to about 6' below surface, then dirt. I dug the holes manually, which was harder than...

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Okay so I had a fence get blown down (posts where rotting and they snapped at the base) the past weekend. I would like to replace the fence myself but right now things aren't going so great. I can dig down pretty easily w/ a post hole digger until about 10" or so and then I hit solid rock. I moved down the row to the next spot and the same thing. I tried using a breaker bar to bust up the rock and while it does help, I'm only down another 2" in 45 minutes worth of work in 1 hole.

I've got about 80ft and I need to dig 10 post holes. My plan was to rent either a 1 or 2 person earth auger, but now I'm thinking there's no way the earth auger would get through the rock layer that's a foot down. Anyone run into something simliar when building a fence? My only thought to make it easier would be to rent a jackhammer but I'm not really certain how great of an idea that is.

I figure i would seek the advice of the experts at the lounge.

How far down are the original...
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