Tunnels are darn near impossible to destroy in Civil War times - and even later for that matter.
To properly do so you would have to bore holes into its face like coal miners do and then pack in powder. When that exploded it would tear out huge chunks of the wall and, if located near the ceiling, might drop that too.
However, no Civil War armies carried such equipment to do this and, as such, tunnels were never brought down - except one. The Galltin Tunnel north of Nashville was dropped for a time by John Hunt Morgan. This was cut through a soft shale hill, rather than the typical limestone, and it was supported by wooden timbers. Morgan set a train on fie and pushed it into the tunnel, where the timber supports burned and the tunnel dropped. It was repaired and the L & N Railroad was back in business within a few months.