Can somebody who is an engineer or is familiar with the tunneling process explain why boring machines are used for tunneling rather than explosives? It seems to

Can somebody who is an engineer or is familiar with the tunneling process explain why boring machines are used for tunneling rather than explosives? It seems to me the primary energy costs of tunneling are associated with converting hard earth/boulders/bedrock into rubble and then transporting that rubble out of the tunnel. Thus explosives (if properly and efficiently delivered) could deliver far more energy than a boring machine in the same time period. What I am proposing is that instead of using a boring machine to use some kind of mobile gun platform instead. The platform would analyze with GPR the best place to fire an explosive round (through the partially cleared rubble) into the untouched earth behind it. It would then analyze the placement of the round and (depending on the ability of the round to adjust the direction of the explosive charge) detonate to increase the tunnel size. The rubble would act as a buffer to lessen the effects of the explosion inside the tunnel. Rubble could be cleared by conventional means, although electric trucks would be superior from a toxic fumes perspective. Tunnel stability would have to be handled separately. Appreciate any feedback on where I am going wrong. I am guessing there may be cost issues with the explosive, inability for rounds from the gun to penetrate very far or accurately into the earth or safety issues with explosives that would slow things down. The latter could be dealt with though if the gun platform and trucks were self-driving.