11 foot steel post in concrete ?

[rexrapter1234]

I have a steel square pole that is 11 feet height, 11cm depth and 11 wide.

The post is for a wooden heavy gate which is 4 foot high and a bird house at 7 foot high from the ground.

If I float the 11 foot steel pole in the concrete at 3 foot with bolts coming out of the steel pole at the bottem, would that work ? or would I need to put in steel bars in the ground with the concrete ?

Also will be putting back top soil and there is lot of big rocks under the ground where I am digging the hole (there is an old building foundations in the ground where the hole will be.

Thank for reading

 

[Tigercubrider]

Not an expert but £20-25 spent on a fencing spade will allow a good deep hole without disturbing the pack of the soil. Even if you need to smash concrete or brick rubble.
A fence at six foot needs 2 feet of post under.
When I did my gatepost, I added various bits of scrap rod to the concrete

 

[r896neo]

A post hole needs to be firm undisturbed ground. You must not backfill anything other than concrete or rubble mixed in with the concrete. If the ground is very loose you need to compensate with sheer mass of concrete to make the post stronger.

You don't really need the bolts if the post is square it won't rotate. The force of the gate is levering not trying to lift the post vertically.