Overturning resistance of embedded post

[TJW]

Can someone give me a "quick and dirty" way to estimate how deep I would have to embed a post in dirt to resist a horizontal load at the top of the post without overturning?
This is just a stupid little backyard project for the kids. If it was at one of their friends houses, their dad would probably just dig a hole that looked deep enough, pour in some concrete for good measure and his kids would be playing on it while my kids are waiting for their anal engineer dad to finish scratching his head saying "I know I can figure this out...." So if anyone has any advice that would ease my mind, it would sure make my kids happy!!
Thanks,
TW

 

[IRstuff]

What level of load?

TTFN

 

[jec67]

The problem you describe is similar to the "flagpole problem" that is ofter discussed in Foundations Engineering textbooks. I do not have acopy in front of me at the moment, but the basic method of solution is to treat it as one would treat a sheetpile retaining wall. The formulas are usually modified to account for the fact that the loading of the soil is not a plane strain situation, as well as the loading differing from the soil loading on the back of the retaining wall. Check out a foundation engineering book for the details.

By the way, when I built my daughter's playset, I just dug a hole and stuck the post in

Regards

 

[Lutfi]

Gaylord and Gaylord have the best dissertation on this subject matter and they cover it in about two pages. Get a copy of it and follow their recommendations.

I developed a spread sheet to do the embedment form me and it works fine. If you can not get Gaylord and Gaylord, let me know, I have an excellent chart that you can use.

Good luck

 

[Lutfi]

My rule of thumb is embed the pole 1/3 it’s above ground height. This rule is conservative but good to do preliminary estimates.

 

[TJW]

Thanks for the replies. I have an OLD Gaylord & Gaylord book, I'll see if it has what you referenced.
Lufti, if your chart is handy I wouldn't mind taking a look at it. My email is wolfetomj@msn.com or a fax is (360) 668-3153. Thanks again,
Tom W

 

[Taro]

If you have access to a 1997 Uniform Building Code, check out Section 1806.8.2. Equations are given for the embedment depth of a pole foundation required to resist a lateral load. Let me know if you can't track down a UBC and I'll email you the relevent section.

 

[JRGse]

I agree with Lutfi. Another good reference is Post-Framed Building Design Manual

 

[Lutfi]

Tom,

it is on its way.

 

[Joecandraw]

I have put my whole design team on the problem at hand. We feel that the architect should be consulted before the hole is dug.
The rule of the day is the design is determined by the actually conditions of use. If it is a pole for a flying genny. Make a deep wide hole and use alot of concrete. Truth is people get hurt by poles that fall and children are hard to come by. Use some concrete in the hole because it is safer. Go get some quic crete i think they are like 3 dollars a bag. But also you have to know kids play on poles, the run into them, they hang on them and they even climb them so provide a anchor for the pole if it is very tall. The concrete should weight about three time the weight of a child. I know a child that was almost killed by a pole that had very little concrete in the ground. She was playing on the pole when it overturned on her. If not for GOD she would have died. Safty First. So make the hole wider at the bottom and use some concrete to anchor the pole.
The 1/3 rule will work, but add some concrete about 150 to 200 lbs.