looking at your photo, my first question is what is the bridge over? if a ravine, does it flood badly? i assume you built it 2' above grade for a reason. if that reason is because the ditch under it fills with that much water, i think your biggest concern will be your ramp fill sinking into the ditch and eventually plugging it. if you can find some large, cheap, culvert pipe to place under the bridge that will handle the water, i think your long term prospect of success will be better.
at least in our neck of the woods, the freeze/thaw/rain cycle is what does in any kind of embankment that isn't properly stabilized. without being able so "see down" under the bridge, i think your biggest concern might be the banks around the support erroding away and the ramps slowly caving in in that area.
on the other hand, if it stays dry all the time, you might not have any problems... ;-)
amp