How are pigs living on a gravel floor?

I have a old gravel driveway running through part of my pasture. Since I can't really use this area for other animals nor growing stuff since they laid about two feet of rock on the ground there, I thought it would be a good spot for a permanent pig shelter.

I'm curious if anyone has done this and what effect the pigs will have on the gravel?

what is the water flow like when it rains?
When it is wet and cold the pigs will want some place to stay warm and dry.
When it is hot they will want a cool place out of the sun.
A friend of mine used sand over gravel for good drainage and to provide a place where big hogs can get comfortable.
That is also one reason they like mud, they can cool down but they can also move the wet earth around to make themselves more comfortable.
Every mudhole becomes a custom pig bed. With moist sand they can do the same thing with less mess. Sand over your gravel might provide a well drained environment for hogs to bed in.

It has shade ad it's on a high point where no water can flow into it. We're going to build them a little shelter soon. Glad to hear that your friend had success with the sand and gravel.