How deep is deep enough

[DavidPerry]

I'm thinking of making a pole barn. I am planning on the poles being 12' above ground and 4' in a auger hole with concrete. Would I realize any benefit from driving the pole deeper than the 4' hole? The ground here in NE Texas dries and cracks badly. I can see 2' deep crevices in my pasture.

 

[k7oi]

DavidPerry,
I live in the wetter Seattle area, so I don't really have a definitive answer for you - but I've been in your area and have marveled at the wildly tilting power poles common down there! I suspect the power companies sink their poles at least four feet, so you might expect similar movement at that depth. Hopefully you'll get a better answer than this, but I'd go deeper!
Good luck,
Terry K7OI

 

[Soundguy]

4' sounds good.. that's what my polebarn is. I also dropped a square concrete pad in my holes for the piles to set on.. then backfilled and compacted. My structure is 24x36, tin roof, and usesd 8x8 as piles.. has withstood 6 years now.. the last 3 of them being VERY hurricane active here in florida... nothing even budged on my barn...

Also.. the concrete really isn't needed... You are employing a friction pile construction method. The 'crete will help with extraction resistance on side loads and won't hurt much ( some woods don't like 'crete' entombment.. ).

For more info on this.. google friction pile....

Soundguy

 

[accordionman]

HELLO TO ALL,
my comment on your project. do not use
concrete around the post. when the company
was building my pole barn, i ask about this,
they said, we cannot guarrantee it for 30
years if we used concrete around the post.
they said concrete around the post would
draw moisture, and cause premature failure
of the post.
they put a concrete pad in the bottom of the
hole, and the post rest on this. the hole is
then filled with dirt, and compacted. this was
21 years ago, and i have not had any problems.
accordionman
wlbrown
wright city, mo.

 

[Farmwithjunk]

Common practice in these parts is to backfill around poles with dense grade and not dirt. That said, I used dirt on mine. Built one 25 years ago at the old place and it's still sound as a dollar.... Let me re-phrase that....solid as a rock.

 

[dooleysm]

Rule of thumb is 1' down for every 3' up, according to my architect brother in law.

 

[wroughtn_harv]

I'm thinking of making a pole barn. I am planning on the poles being 12' above ground and 4' in a auger hole with concrete. Would I realize any benefit from driving the pole deeper than the 4' hole? The ground here in NE Texas dries and cracks badly. I can see 2' deep crevices in my pasture.

I've just about decided that in this north Texas clay four feet isn't enough for fence posts. :>(

I've watched fence lines jump up, down, and sideways just from the movement of the clay in this drought.

I've got some fences in sandy soil just north of here that are straight as an arrow three years after installation. There are some closer in the clay that have an austin or limestone rock layer about eighteen inches down that are straight and true almost twenty years later.

But when it's just clay it seems to take only a summer to have the posts moving.

It's all about expansive soils I guess.....but then it moves homes, swimming pools and why should we be surprised when a fence post moves?

 

[DavidPerry]

What is the thoughts on driven post rather than drilling and back filling a hole?

I have air powered post driver I've been trying to find a reason to use.

At $1.5 / foot, the cost of the post 2 or 3 more feet deeper in is not a big deal if it would secure the building.

 

[Soundguy]

I'd dig, add pillow, insert post, and backfill and compact in lifts...imho..

soundguy

 

[MF1455v]

David, what type of post are you using? With you thinking of using a pnumatic post driver I assume you are using pipe.

IMO in this black land dirt, you have to get below it into something solid or the post will move. On my place white cleatchy (not sure of spelling) clay is between 4 and 5 feet deep. Its most interesting to see the ground move away from a post in drought and when the rain returns watch the post pushed out of the ground. The Texas version of frost heve.

My carport posts are 16ft 2 7/8" pipe. I have 8ft clearence above ground. That put them only 4ft into something solid with concrete all the way to the surface.

James

 

[CharlieTR]

I don't think deeper will add any strength to the structure. For mine (in Ladonia, TX) I just poured 1 foot of concrete below each pole, backfilled with concrete, then a couple of years later added a concrete floor. It seems to me that the massive cracks we get here are limited to pasture areas, rather than real close to structures. A little rain, dew, shade is enough to keep the soil intact around the barn, at least not nearly as bad as fences.

 

[DavidPerry]

Yes, I was planning on using 2 3/8" OD pipe for the uprights. I'll add a concrete floor. Maybe it will all be a non-issue with the floor down.

Thanks for your input.

 

[DavidPerry]

I looked at some pipe this evening I had driven 3' into the ground this last spring. I could lift the post out without tools. The posts in 3' of concrete are still steady. I think I'll go with 4' holes and a bunch of concrete. Hard to believe ground can crack and split this much.

 

[wroughtn_harv]

One of the biggest problems we have in my line of work is trying to find that combination that will keep a post located over time.

In sandy soil there isn't the problem with heave or better yet, expansive soil contraction-expansion that we have to deal with in our heavy clay.

My son in law saw a bull snake dive into a crack by his house. He grabbed the tail and tried to pull it out of the crack. The snake was too strong and finally son in law let go. The snake disappeared and not a part of him could be seen.

Probably the best example of the way we have to engineer and build things just because of our soils is our street construction. Most parts of the country a simple base preparation and then blacktop is standard for most residential and rural roads. Here in the cities the soil is first stabilized with lime treatment and then serious concrete is poured. And this is for streets in subdivisions. On the major highways it's even more involved.

When the soil presents such problems for major construction then simple things like setting fence posts or poles for barns and shops have to be treated differently as well.

One of my clients has forty plus acres in Rockwall County. His house sits on a rise (we don't have hills much less mountains). His elevation will change six inches during the year as we go from wet to dry. When they built his house they went down forty plus feet with the piers and never found anything but clay.

 

[DavidPerry]

Today I removed the last of the pipe from this area tackling the only one of the bunch that didn't just fall out of the hole. This was firm and not in a hurry to come out. I had driven it 7ft below grade.