Yeah that could work, but dirt stops bullets too, and it will stay where you pile it up and doesn’t evaporate. If you want to penetrate a defended earth-berm structure, you may need explosives.
Yeah...and dirt doesn’t splash so much!
In thinking about the zombie apocalypse, I imagine an upstairs room with a window and a good view. Then some sandbags and some pieces of plywood behind that would handle things pretty well.
Unless of course the Zombies have RPGs, molotov cocktails, or a match.
How many mud balloons would it take?