Pole Foundation

[Okiryu]

Hi, I am providing recommendations for pole foundations. I am recommending drilled piers of 0.8m diameter with 2.5 m depth of embedment. This is for electrical poles of approx. 9 meters height and 0.3 diameter. I am using ASCE 7-10 and IBC 2012 to calculate wind loads and drilled pier embedment. I cannot find in the Codes if this type of small foundations require reinforcement. Are these type of foundations reinforced? Thanks !!

 

[Okiryu]

I am assuming that the post will be embedded in the drilled shaft, so there will not be too much space to place reinforcement?... any comments?

 

[NOLAENG]

ACI will have the requirements for reinforcing.

 

[EngineeringEric]

I have seen them unrienforced for signs. I may get beat up for it, but i have specified them without reinforcement.... Mine were not poles but some temporary foundation elements.

 

[SlideRuleEra]

Okiryu - In the USA electric utility distribution poles are almost always directly embedded in soil, no concrete. Embedment depth is determined using an estimate of soil properties, height of pole, and any external loads on the poles (say, overhead power wires going to other poles). You did not mention the pole material. A link to the US Department of Agriculture (Rural Electric) specification for embedment of concrete and steel poles is given below - it goes into quite a bit of technical detail.

If the poles were directly embedded in soil, 2.5 meters may be shallow for a 9 meter pole. Consider using the info in the link to revisit that depth calculation. I see nothing wrong with using concrete around a pole placed in an augered hole - unreinforced concrete should be ok. If you do use concrete, check with your electrical engineer to see if extra steps are needed to electrically ground the pole or any circuitry on it.

http://www.rd.usda.gov/files/UEP_Bulletin_1724E-205.pdf

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[boo1]

There are two typical standards for electrical distribution pole design – National Electrical Safety Code (NESC) and
the American National Standards Institute (ANSI O5.1)

see post

http://www.eng-tips.com/viewthread.cfm?qid=391120

 

[Okiryu]

Thanks for the responses. They are very helpful. The USDA guidelines is interesting. I am sure that I will have some comments from our client, so I will use all these reference to revisit my calculations. Thanks again !!

 

[Canuck67]

In my area they augur the holes for the poles slightly oversize and then after setting the pole in place they fill the remainder of the hole with limestone screenings which compact very well and generally provide good load transfer from the pole to the surrounding undisturbed soil.

 

[Okiryu]

Canuck, thanks for your reply. Just one comment: if the depth of penetration is deep, are you still using soil to fill the remainder hole? Compaction may be difficult to conduct if the hole is just slightly oversized. For deep penetrations, does not concrete work better?

 

[steellion]

For cylindrical pole foundations, we typically use 0.5% vertical steel and minimum column ties per ACI.

 

[boo1]

Gravel, or unreinforced concrete are commonly used for around the poles.
I have even seen injected two part foams used with weak soils (Arkansas clays).

 

[Okiryu]

Thank you all for the great references !!