I made a little experiment to see how much bodyparts there would be after the destruction of 20 thrall, 5 dwarves and 4 wights. I used "For carnage apply within".

First, fill the bottom of the pit with satchel charges.
Then put all of your men upon them and fire bombs in the middle of the satchel charges.
The satchel charges starts to explode from the middle and the thrall starts to get wasted.
The explosions soon reach the wights and we all know this is the end of the army.
Everybody is being torn apart except for 1 thrall and a dwarf. Last man standing :-D
Ouch!!! Casualties...
Things seem to calm down, the last pieces of the army flies towards god.
Nothing left except for a wights head and ashes mixed up with blood and gore.

Don't try this at home kids...