Have an existing concrete driveway want to bring fill dirt and pour a concrete slab for a garage over the existing driveway.is this possible

Could you clarify for us? Are you talking about leveling dirt on top of the drive and then forming up a slab pour on the new dirt? This won't fly.

You will need to remove the old slab and pour a new slab for the garage. Are you building a new garage over the existing driveway?

Yes I am pouring a new concrete slab over the driveway conmcrete after I bring in the fill dirt

OK thank you for your answer. Could I pour a new concrete slab directly on top of the driveway concrete slab

The problem with pouring a new slab over another slab is if water gets between the 2 slabs it will freeze and heave damaging the new slab. You should remove the old slab.

I agree, you should remove the portion of the drive that will be under the new garage. Also, keep in mind that a slab pour should be backfilled around the gravel base to keep the gravel from moving. This may affect the grade around the old driveway so setting a new slab as low as the drive is a good idea.

I live in houston water never freezes should I still be concerned

The final answer will depend on wheather you need a permit or not. Most city and state codes will not OK what you plan. If no code/permit issues then you probably could get away with it but the slab would still need to be full thickness of at least 4" reinforced inches of concrete. The reason I say get away with it is contrators would not do this type of building.

Yes, anything is possible. We're telling you the "right" way to do it.

I would remove the slab. The slab under the new one will move differntly than the one on top. It will create problems down the road. I have never seen it done without causeing issues.
Mike

What is the cost of concrete per yard?

It is going to varry from state to state but where I live in Iowa:
3500 Mix = $77.00
4000 Mix = $85.00
Fiber Add = $8.00
I would call your local ready mix plant to find out for sure
Mike

O.k. I would remove the old slab, dig a footer, which hasn't been mentioned, and make one pouring of the footer and slab. The reason for the footer is to support the structure.

Based on where you live I would pour a " floating slab". Set your 2x4 or 2x6 forms like normal, then dig out around the perimeter of the slab. You want to dig down and in about one foot. Lay two rows of rebar into your perimeter, tie a 90 degree rebar to those and attach to the slab re-enforcement. ( rebar or mesh ) Since the ground never really freezes in your area the thickened edge will be you footing. Check your local codes to double check 1' x 1' footing, but that is all they usually require.
Mike