Idk if you've realised it already but it isn't the best idea to have the wooden debrees on the "ground" after falling off. Most walls on terrain aren't exactly leveled and it would lead to some debries being underground and, worse, some floating in thin air.
Otherwise awesome job, this'd be nice to see implemented. I take it you're replacing the current walls with these in a way that you won't need to remake maps? Not that i'd mind having all strategus siege maps balanced along the process...