Who made the tower? What is the model number? Is it a crank up or not? What are your soil conditions? Where do you live (seismic area or not)? Do you have pictures of the current installation or closeups of the tower? What antennas do you plan to install? Are you on a hill top, or in a valley? Are there any tall obstructions nearby that will deflect the wind? Do you have any measurements of the tower legs? Is it currently guyed?
The above questions need to be answered before the foundation can be designed. I recently designed a foundation for a 75' Rohn free standing tower. The manufacturer design details were severely lacking in terms of minimum reinforcement requirements (they didn't meet ACI Code requirements) and were not applicable to the local building code requirements. His system utilized a 5 cubic yard mix as it is the minimum truck order (you'd have to pay this amount for anything less, locally, so might as well get a full 5 yards).
Find out what your minimum order is from local suppliers as you don't want to try to field mix a tower foundation unless you absolutely have to. The proportions can get screwed up too easily in the field.
EDIT - Before anyone asks about it, I'm a licensed Civil Engineer and do this type of work routinely. I am willing to offer advice on how to proceed, but cannot complete designs for your location. Sorry, but it's just how my employment contract currently reads.
In my not so humble opinion, I don't think I would want to install a used tower unless I had the correct mounting base from the manufacturer. I also would not want to re-use a mounting base (that is if you could even dig it up).
First of all Thanks to both you that answered so far. Im not sure about maker of model # and here is the story of it as he told me he bought it off of someone and it was in the ground this guy cut it off at ground level then they made the pad in the ground then ran rebar welded to a plate into the concrete then put 2 hinges on it welded those the the plate and another plater bolted down with to screws and rebar running from the top plate into the tower post and welded to the plate so that is all about that he was using it with a huge cb atenna on it. Soil conditions swamp like water table not to far down maybe 3ft give or take depending on rain. Im in nw indiana and no pictures also i couldnt say no because he paid 100 bucks for it from a friend then im going to get it for 50 so cant beat that and its in pretty good shape. Kinda in a valley im about few half mile if that from the river. Alot of trees couple close to were the tower would be and most of the surrounding woods anywhere from 50 to 200 feet depending on direction. No measurements i seems just like they used a 10 foot section in the ground and he cut he when he got it and its about waist height. Not currently guyed pivoted up to the house then bolted through plate and mounted to house. I would of loved to get a new one but lacked the 1000 dollars or more so for 50 i cant beat it just try to figure out how to get it down so i can buy it. Im putting 1 ST2 and 2 800 mhz yagis. THANKS FOR THE HELP GUYS BLESSING TO ALL
Good advice already given. Let me give you MY exact experience.
I have 50 feet of Rohn 45 tower on top of a large hill in a very windy section of Wyoming.
The Rohn specs were a 36 inch diameter hole, 6 feet deep, filled with concrete and the base support structure, in undisturbed soil. Bracketed to the house and 1 full set of guys at the top. Built to take 110mph sustained winds.
While I cannot give you certainties, I know a LOT of self supporting towers of your height pour concrete bases 5ftx5ftx7ft deep. This is a LOT of concrete. But think of the bending moment at the base of a lever that long. You need weight there.
From the sounds of it, this tower has possibly been abused or reutilized several times over the years. I'd be leary about putting it up as a free standing tower without some guying. If you are determined to have it be free standing without any sort of guying or bracing, be sure to go over every weld to ensure there are not cracks. Also check all of the members for breaks, bends, cracks or other deformations.
Your soil conditions are not great for putting in a good foundation. You will probably get some frost jacking of the foundation and it will be tough to pour concrete with the shallow water table. You may want to look at a precast "pile" or similar foundation system to get your foundation below the water table slightly.
It doesn't sound as if you will have too much issues with direct wind loading, but you will want the minimum amount of concrete recommended by the manufacturer to start out.
If you can bury a section of tower into the concrete base for your new foundation with plenty of reinforcement to tie everything together, you will loose some height, but it would be a stable foundation. Getting it to the site and installed could be an issue if it is a boggy area. Equipment likes to sink and I wouldn't want to try to get a concrete truck into a swampy area (drivers don't like getting their trucks stuck).
As to removing it from it's current location, get your hands on a gin pole and a tower jack, then start removing it one section at a time from the top down (IF you can safely climb it). If you are unsure about the climbing aspect, rent a zoom boom forklift with a basket. Have someone tied off in the basket will all appropriate safety gear, tie off to the tower above the middle with enough slack to rotate the tower, raise the tower section slightly, release the bottom, then continue lifting until clear. Once clear, rotate the tower and lay it down on the ground; then disassemble into the 10' sections.
Good luck on the project, it is a good price for the tower; be safe with it's disassembly, relocation and installation.
I would highly suggest not "burying" a section of tower into concrete. Not a good practice. Mainly, because if it is a hollow tube tower "which im sure it is" the legs may start to rust VERY quickly where the legs become incased in cement, sometimes from the inside of the legs working torward the outside. Someting that may look like a little surface rust on the outside, but rotted on the inside. My advise, get the model, get the specs, get a baseplate and proper foundation according to height. Install the tower properly.
Thanks for all the help i kinda changed my plan some and this is what it is. Instead of going self supporting im going to go with it concreted in the ground next to a pad that was poured when our house was built ( didnt see that happen just my conclusion) they put a pad i think maybe for a tower a long time ago so my other buddy has 1 inch rebar and im going to drill holes in the existing pad put the rebar in set the 10 ft section in new concrete with the rebar connecting the 2 together witch im pretty sure the existing pad is also connected to the foundation of the house from when the first poured it. The existing pad is like 5 ft wide at least and a good 3 or 4 maybe more ft deep. So any comments about how this idea might work plus then it would be connected to the eve of the house also. Thanks for the help and Blessings to All
This route may work if you utilize the proper epoxy to tie the bar into the concrete and have a good embedment. It also sounds as if you'll be able to tie the side of the tower to the house near the ridge-line (also helpful). You will want to order or make a bracket to catch two tower legs and have them attach to the home with lag bolts; you'll want to seal all the holes with silicone as well.
You can also purchase the proper tower base once you know what kind of tower it is, embed some bolts into the concrete with epoxy and bolt the base down; then attach the tower to that. Would be cleaner than trying to get the bar into the tower legs and getting the tower legs tied to the bar.
You may want to go to 1/2 of the depth for either the bolts or the rebar as a bare minimum due to the unknowns and use a Redhead exterior grade epoxy (Epcon A5 or equal). Hilti epoxy's are better, but much more expensive. Be sure to properly clean the holes before inserting the epoxy; this is a critical step.