but I can think of nothing else that would aid a rapid demo more, that wouldn't also be prone to problems
Literally drilled holes? I googled this a bit and they call them "charge pits". I find it weird they'd call them "pits" if they're just rebar they hang explosives off of.
You don't decide to blow a bridge willy-nilly, and they need to have explosives anyway, and since the bridges are blown in advance, I don't think they'd be in the middle of a tactical retreat.
Blowing up bridges with methods you decide during peacetime is strategy, not tactics.