Utility wood pole soil embedment design
Utility wood pole soil embedment design
(OP)
Hi,
How do you verify the ground stability for an utility wood pole ? I know that the rule of thumb is 10% of the lenght plus 2 feet. But is there a way for more accurate design based on the type of soil and bearing resistance ?
gasma1975
How do you verify the ground stability for an utility wood pole ? I know that the rule of thumb is 10% of the lenght plus 2 feet. But is there a way for more accurate design based on the type of soil and bearing resistance ?
gasma1975






RE: Utility wood pole soil embedment design
BA
RE: Utility wood pole soil embedment design
Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.
RE: Utility wood pole soil embedment design
As a side note, I was just trying to get some pdhs for license renewals and I thought the course would be easy. But it turned out there's a lot more to wood pole design than I thought. The course was involved and the test was very challenging, with a lot of problems to work.
RE: Utility wood pole soil embedment design
I'd suggest getting Bulletin 1724E-200 ( http://www.rurdev.usda.gov/SupportDocuments/UEP_Bu... ). Chapter 12 is pretty consistent with what seems to be standard practice.
I've got a good recent study that modifies some of that, but I can't figure out where I've put it.
RE: Utility wood pole soil embedment design
RE: Utility wood pole soil embedment design
RE: Utility wood pole soil embedment design
First decide how you're telling them what they need to install. Are you giving them a cable length to install? An installed horizontal tension? A variety of installed tensions depending on the temperature?
Check your loading based on the cable weight, the weight of the attached load, the weight of any icing, and wind. Some people like putting bird allowance on too. I mostly just like saying bird allowance.
In addition, you have to account for temperature variations. You'll install at some temperature and then later it will get warmer and colder. The former increases your sag and decreases your tension while the latter does the opposite. For a distribution line you'd normally do this with a sag chart. You have a chart that tells the installer what sag and/or horizontal tension it's supposed to have at a given install temperature so that at the hot and cold temperatures the sag and tensions are what you expect them to be. In general, you'll set all your variables like this:
Determine your maximum allowable sag. This occurs after creep and at your hot temperature. So you set your tension or cable length based on this condition and based on your sag. If you're using steel rope or something, creep isn't as big a deal as it is with overhead conductors. With this case, check where your wind is going to push your cable to horizontally if there are clearance issues. This will be your biggest swing case.
Now that you've got your start point, look at it with your minimum temperature, ice, attached load and some/all the wind. This generally gives you your worst case design load.
Take that load, apply it to the pole. Check the pole structurally and for deflection. Get your baseline moment. Design your embedment to take that moment as per the reference I provided. Note that utility pole designs tend to deflect by amounts that would be crazy in most situations structural engineers would be involved with. If those aren't acceptable in this case, you may have to look closer at your embedments.
That reference actually goes into utility pole design in general, so you probably want to look through it. In standard installs it's pretty easy because everything's generally been tabulated by someone, but when you start trying to do anything even a little non-standard there's a lot to get your head around.
RE: Utility wood pole soil embedment design
RE: Utility wood pole soil embedment design
BA
RE: Utility wood pole soil embedment design
RE: Utility wood pole soil embedment design
Michael.
Timing has a lot to do with the outcome of a rain dance.
RE: Utility wood pole soil embedment design
I saw in some documentation that is not allowed to put concrete around a wooden pole, is it true ? normally what is the detail construction when you embed a wooden pole in the soil ? I guess you put gravel at the bottom, what is around the pole ? just the soil or can I add some compacted crushed stones around it ? I cannot find any detail on the web...
RE: Utility wood pole soil embedment design
BA
RE: Utility wood pole soil embedment design
I agree, and that's why I put 3 to 6" of gravel at the base of the hole, install the pole, and pour concrete around that for pole buildings. With that, you do get the drainage you need, assuming you are above the water table.
For fence posts, I jus use a dry mix concrete, hand tamped with the gravel at the bottom. My PT fence posts have been in the ground for 30 years and are still very serviceable.
Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
RE: Utility wood pole soil embedment design
Dik
RE: Utility wood pole soil embedment design