Gate posts depth

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Ground is DG and hard as a rock. Can't dig without machines.

Post is 4x4 steel with 1/4" thick wall.

Posts will also be filled with concrete. Much less bend factor there.
 
4' in the ground and 6' out. Gate weight 300 pounds. Probably at least 400 pounds of concrete underground.
 
I really don't see a problem. I have a 200 pound gate secured to a hollow core block wall and it doesn't budge a bit.
 
Will do. It will probably be a few weeks. We are slammed with work right now and they need to be hand dug due to my main electrical feed and fiber optic lines close to where the posts are going. Don't really feel like ripping out either one.
 
Wait a “moment”!

Neal is correct. Here is a link that starts off pretty basic and then quickly gets heavy.
https://en.wikipedia.org/wiki/Bending_moment
Neal’s flag pole example or more importantly the fishing pole example is a great example of bending moments and how they can be used and understood in making something as strong as possible. In the case of a fishing pole the bending moment moves along the length of the pole as more load is applied and progressively moves to a larger section of the pole with greater strength to react the load. As the pole bends the weaker smaller area becomes more in tension and less in bending as it curves. As a kid you might have fished with a homemade pole made from a sapling and you somehow knew to tie the line to the small end that it would work better that way. The Eiffel Tower is another great example.

In the case of the pole in the ground there are a lot of different forces going on as the weight of the gate assuming the pole is attached to the ground in such a way nothing below ground can move. Then then the highest bending moment would be right at ground level in a static problem and that was what I was describing. The fishing pole is more of a dynamics problem as are almost all real world problems as things do bend and move. In the real world the pole will bend and the soil below the ground will be reacting in one direction at the base of the pole and another at the top of the pole. So the real problem asked was how deep to plant the pole? That totally depends on the depth and the rate of soil compaction and the area in contact with the soil. Pouring Concrete around the pole adds weight but also makes the pole bigger and pushing on more soil just like how a footer works below a wall. From a soil stand point deeper is better until the amount of reaction given is greater than the bending moment will allow at that point going deeper is just wasting money.

At what point are we going to start referring to Chris’s new home as “The Compound”. :)
 
You could always post the name of your ranch above your gates as "Rancho Longlastname", but you will have to widen the gate opening by about 20 yards.
 
I have motivated one of my neighbors to start cleaning up his place. Two more neighbors to go and this will be a nice looking street.
 
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