Jolougarcia:
I was pulling your leg, in the hopes of getting you to think a little. You do have to use some engineering experience and judgement to design almost anything meaningful and useful to the world. And, if you ask your question on a forum, the way you did, there are many answers, you have to give use some clues if you want meaningful answers. We can’t see it from here. Talk with the transformer manufacturer about what they expect in the way of a foundation. What size is it and what does it weigh in operation? What are the soil conditions? Is this a large transformer at a power plant, a couple hundred tons maybe; a smaller transformer at a sub-station? The one in my front yard steps down the voltage from a main power line and serves six houses.