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I am installing a 22 ft. steel light pole. I picked it up used so I don’t have any manufacturers instructions. I haven’t decided yet what lights I will mount on it. I am not sure how deep, or what diameter, I should make the concrete base. We have fairly strong winds in this area. I am thinking of approximately 4 ft. deep by 18″ diameter. I will use #4 rebar to build the cage and use about 36″ long anchor bolts-sound ok? If I use a backhoe to dig the hole it will be larger than necessary. I will use sonatube for a concrete form. Is it ok to fill the dirt back in afterwards and either tamp it well or compact it with a jumping jack?
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What is adequate will depend on soil conditions and pole loading from whatever you are going to put on it. So, first figure out what you are going to mount on the pole and where. Then call you friendly utility company's engineering shop to get the straight scoop on just what your pole is designed to support and what kind of foundation it requires. Also, I've heard of poles that are designed to fold at some pretty low loads to minimize injuries if hit by a vehicle so that is something you might want to check out.
*What you propose sounds Ok, but I would consider digging by hand or with an auger and using no forms. Oversized holes invite trouble. If you do use a back hoe, dig just wide enough for your tube and hold it up of the bottom to let concrete spill out to make an upside down T that will lock it in. Compact well.
*We did one recently that was hinged at the base to make bulb replacement easier. It was 10 metres and we augered a hole 1800 deep by 450 wide with a spiral cage of 4 x 16mm deformed bar for reo. welded onto 4 x 16mm treaded rods for base attachments.The lights were 2 x 250 watt sodium and lit an area of around 500 sq meters.
*I put up a million big sign poles and we didn't ever form the base, just dig a real clean hole. When there is any doubt, (such as no engineering), dig it deeper and fill it up, concrete is cheap compared to failure. Do you know how to position the bolts?---Cut a plywood square a couple inches bigger than the bolt pattern and drill holes where the bolts go- use the pole base for a pattern. Attach bolts to plywood just as they will be on pole and support this rig over the hole. One nut above and one below the plywood, Thats how you plumb the pole later, too. Place concrete and template holds bolts. Pardon if you already know all this.
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