The problem with mud is that fresh gravel tends to migrate downward into it, and disappear. I have built a lot of new homes in an area with extreme clay, as in typically 40-60' deep, according to the well driller. My excavator starts with a base of big rock, often softball to half gallon jug size, then covers this with smaller stuff and a topping layer of "modified" which is the regional name for a mix of everything from 3/4" material down to stone dust. This creates a very long lasting driveway that does not get lost in the mud.
Mud can be an issue of poor grading, when the water flows into the driveway, instead of away from it, or just poor overall soil conditions. If you are working in a really wet area, one good option is a geo-fabric which is a tough synthetic "tarp" that is laid down under the driveway material, and prevents the rock from mushing into the mud. Not very expensive, particularly if you are battling mud puddles, soft spots and constantly disappearing gravel. The whole concept of disappearing gravel might seem a bit strange, but think of it this way. You make a giant batch of chocolate pudding and fill a five gallon bucket with it. Now put two inches of gravel over the top. When you push on the gravel, it slowly sinks into the pudding. You can either continue to put more gravel on top, or figure out another solution. If you start again, put a layer of fabric on the pudding, then the gravel, the fabric keeps the gravel from migrating into the pudding.
That is why some people end up adding gravel to a driveway on a regular basis, and never seem to get ahead. It doesn't evaporate, but it sure can seem to disappear, LOL
