A little OT--- but barn related

I am in need of a way to have about 60 ton of gravel hauled to my barn. This gravel will be used for a large equipment parking area and driveway.
I have two concrete drives and of course these large loads will destroy the driveways. Gravel must be hauled about 30 miles so small loads would take forever and cost about as much as a new culvert. This culvert will be an extension of my existing 12"concrete coulvert that has about 6" of clearance from the culvert to the concrete. This means that my new culvert will have about 10 or 11" of gravel and dirt over it.
I plan to sew grass over the installed culvert.
My concern is, the depth of the new culvert and the heavy load it supports. Any suggestions, or advice, would be appreciated.

Dump 1st load of gravel on the existing culvert and spread aprox. 12" deep. Back the other loads over the "thicken gravel base". When done hauling, clean up the tempory gravel with skidloader and reuse.

Well that sounds like about 3 loads on a big truck.So you would need to get about a foot of something over your culvert before you cross it with the truck.Back the first load in and cover the culvert,or cover the culvert with dirt about a foot deep at a place wide enough for the truck to cross,or dump the first load and spread it over the culvert with a loader or skid steer.Thats if I understand what it is you are asking.The main thing is to have the culvert covered by a foot of dirt(maybe even more) or something before you cross it.If its soft it would have to be spread backwards anyway.You might need to cover the culvert with dirt before the rock,or maybe a load of something other than big rock like waste or just dirt.Others probably will know better than me.While I have driven a dump truck,it was a long time ago,and I just drove and dumped it where they told me to dump it.Seems like culverts were covered about a foot with dirt,then rock on top of that,but it was 30 years ago,I could be wrong.

Jiles,
I'm a little confused about your real question. But, 60 tons of gravel is a little over 2 truckloads, probably 3 as trucker 40 says. Not sure how many axles on the typical single trailer they use up here in Michigan, but I have 25 ton loads delivered all the time. I also just recently put in a culvert. The drainage flow required a 42" diameter culvert which would have been higher than I wanted, so I got a corrugated steel one that is kind of an oval shape, It was about $400 for a 20' section, so call your county road commission and see about buying it through them. You'll probably get their discounted price. Extending a 12" culvert with a round corrugated one shouldn't be too pricey. I don't think they even allow concrete culverts around here anymore (that is, if you're getting a permit and all). As for fill, the key is to use sand and pack it in 3-6" lifts alternately on either side. I hand tamped mine, no need to rent a vibrating tamper. Don't just dump dirt/gravel in on either side. Once you've built it up and have 6" or so of sand over the top, go ahead and put your dirt and/or gravel topping on it. A properly installed culvert with sand backfill and 10-11" of material over it should handle those heavy loads. Not sure about the old concrete one. What kind of condition, it's in, etc.