If you want, I can engineer the proper mount for your tower.

I believe that you need to take into account the height of the tower, the weight of the tower, if it is free standing or guyed and the weight of the antenna on top of the tower.

With the usually configuration of the 3 leg tower - I can't remember right off hand - but something like 16" between legs - and 10 foot sections - you would need to have 1/2 a yard of cement per each section - hence the hole would need to get bigger and deeper the higher you go.

The hinge is usually made out of steel 1/2 to 1 inch thick - depending on how tall and how much the tower weighs.

The first section is usually only 4 feet tall - not 10'

The tower sections would all need to be bolted together and would need to be polished before assembly if you use a old rusted tower section to ensure that each section would be conductive and not resistive - since you do not want corroded joints to reradiate harmonic's and you might even want to run a dedicated ground from the bottom to the top to ensure that the antenna's have a good ground source.

It isn't just as simple as digging a hole, welding some pipe and plate together and burying the whole thing in the ground.
\ The down side is - when ever you put carbon steel in cement it has a tendency to corrode / rust / fail at the point where it protrudes out of the cement.

If you could make a plate out of carbon steel, weld your tubes to it and drill and tap a bolt pattern to the plate and put stainless steel 3/4 - 1 inch bolts in the cement - 6 inches deep = it might last a very long time with no issues.

Tap Cons and masonary screws tends to pull out of the cement with time.

Making the ultimate tower base will probably cost more then what the tower is worth and the stainless steel hardware - unless you have a source will probably be cost prohibitive.

12' of 1 inch stainless steel rod would probably cost 100's of dollars.