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As to the strength of the driveway, 3-4 inches of concrete, plain or reinforced, probably isn't up to the task of supporting this kind of load, especially not knowing the base condition. Any area of the base material not properly prepared with regard to material, grading, or compaction may be subjected to cracking at the least. A thickness of 5-6 inches would be a more comfortable situation.
Your contractor can always pump the concrete, but it will cost you more, maybe much more. Remember, though, that a gravel, or asphalt, or concrete driveway will each require visitation by some rather heavy equipment. Talk directly to your contractor. They probably won't guarranty against breakage, but you won't know unless you ask.