I’m thinking that this bomb would suck up all of the oxygen in the tunnels and suffocate those who weren’t killed by the blast...the way flame throwers did in the Pacific islands during WWII.
The secret is in the Oxydizer. It has it’s own so the overpressure keeps going even deep into the tunnel after the ambient oxygen is used up. Also the blast can go around corners instead of a straight line. The overpressure goes much further in confined spaces.