It would be interesting to run a high pressure stream of gasoline and oxygen into them. A sort of controlled “fuel air blast” within the tunnels and watch what blows up on the other side.
The whole damn city probably................
Fuel air explosives are probably the best bang per pound of crap that has to be carried and emplaced.
But how can you disperse it optimally down a tunnel 1/4 to 1 mile long?
A motorized cart (or the new guy, after some clearing procedure) emplaces bucket-sized charges connected by a fiber optic command link?
A series of line charge sprayers?
A big fan?
A slow spray until calculations or sensors indicate she’s ready to blow?