I was on run crew for a show a few years ago that was set in a bunker. We had a wall made of sandbags, and halfway through the show there was an explosion and the wall blew apart.
There was a 4 foot high (1.2m) platform across the back of the stage, and sandbags were built into the front of the platform as facing. Then on top of the platform there was a structure, I'm not really sure how to describe it other than a ladder. It was 12 feet tall (3.7m), still stretching the full width of the stage, with three "rungs." The rungs were maybe about 2 feet (0.6m) deep. The ladder structure was angled slightly toward upstage.
We started preset by draping a huge muslin drop over the second rung of the ladder, and then we packed it with sandbags (which btw were filled with granulated cork rather than sand - because sand is quite heavy and cork is very light and the cork-filled bags fly pretty well and won't kill you if they hit you), from the top of the platform up to the second rung of the ladder. I don't remember exactly how it was rigged... I believe the drop had pull-cords that came over the back of the second rung. We pulled the cords, the drop lifted up which threw all the sandbags off it and to the ground, and then the drop came through the ladder and fell to the floor behind the platform.
So maybe something similar to that, but obviously one for each section of the wall? If you have enough manpower on deck to run it. You'd have someone stationed behind the wall, and someone to pull the drop through the back of it which would knock down the stones in the wall. This would of course mean that the structure of the wall remains. I can't think of any way to do it that would make it so that once the walls fall down, you're left with absolutely nothing. If that's what you're going for, this may not be a helpful idea but maybe it's a jumping-off point.
I can't find any images of the actual moment of the explosion from my show, but I've found some press photos and video that show both before (fully built up with sandbags) and after (empty ladder structure). PM me if you're interested in seeing them.