Lateral pressure of concrete pole in circular hollow concrete base

[gasma1975]

Hi,

How do you determine the pressure of the concrete fill in a circular concrete hollow foundation in which I have a concrete pole. I'm leaving 2 inch all around the pole to fill with concrete. But I want to know if the filling is done with 4000 psi concrete is it sufficiant? how can I evaluate the pressure on the fill if my pole base moment is 75 kips*ft.

My pole is 16 inch diameter, so the hole is 20 in.

Any idea ?

Thank you for helping

gasma1975

 

[BridgeSmith]

If you're looking for numbers for the pressure based on the moment you've provided, you will need to include the embedment depth of the pole into the foundation.

 

[azcats]

If the soil 2" away can handle the loading, how can the concrete not? I've seen people here describe the concrete as 'soil improvement' and the most conservative way I would treat the situation is to design the foundation depth using the pole diameter instead of the hole diameter.

The above assumes that the pole itself extends the depth of the hole.

 

[JoelTXCive]

If this is a flag pole, then I think a common detail is to fill the annular area with stabilized sand or non shrink grout.

 

[msquared48]

Personally, I would us more than 2 inches of cover. I would use a 24 inch auger generating 6 inches of cover and some hoop reinforcing at the top...

Look to the AITC for the allowable lateral soil pressure and correct equation to use to determine your required embedment.

Mike McCann, PE, SE (WA)

 

[BridgeSmith]

I assumed the annular space referred to was between the pole and a larger concrete foundation. If it's just a 20" diameter hole in soil, then the strength of the grout in the annular space just has to be nominally greater than the soil, which shouldn't take much. The more important property in that case is that it's very flowable - with a 2" annular space and at least several feet of embedment, your grout better flow almost like water.