Our dirt is a mix of dirt, & sand. It gets everywhere, makes the run a mud bath, & mats up my birds feathers badly. Had to cut golf ball sized mud balls of one of my pullet's belly a few days ago.^I'm not a fan of sand. It only helps drainage till water hits a level that is not sand, and it only drains well until the chickens droppings have caked it up - which in a static run, doesn't take long.
There are those who find sand successful. I'm not one of them, and have not yet discerned what it is about their situation that makes sand work for them.
and for what its worth, my soil is clay-y sands and sandy clay in the area of my run. The sandy loams (which are great for drainage) are unfortunately on the other side of the hill from my coup. I use a series of berms for runoff control (there is an acre of hill above my coup), and dug a shallow depression in my run to help collect rain falling on it, which forms a shallow pond that feeds a broad ditch, which is then directed outside the run and down the hill. I use spent straw from the house and raked leaf litter to add to the ground cover, but it breaks down as fast as i pile it in (I really should rake up leaf litter for addition to the run more frequently - its easily 500 sq ft, so a few bags of leaves really don't make much difference.)
If I can turn the whole chickens yards into a sand run I won't have to deal with that problem.
Plus my coop with my project Orpingtons gets so muddy inside, & out, the floor of the henhouse is covered in 4 inches of mud, if not abit more then that. Gonna be cleaning that coop Monday though.
My Bantams rarely have a muddy run unless a huge severe thunderstorm rolls in.