Great photos. You may be interested to hear that a section of the tunnels you photographed was for some time used as a small-bore rifle range.
The Glasgow Railway Rifle Club was sited in the then long-closed westbound south tunnel that ran from Barrack St towards St Enoch. The range closed circa 1980 I think. Entry was from a now bricked-up doorway in Barrack St which led to a steep and dangerously rickety wooden staircase down to the entrance. Trains would often be passing on the north tunnel on the then active line right beside the sealed-off section which contained the range. The "clubhouse" was on 2 levels and fairly rundown when I and fellow members of the Martin Rifle & Piistol Club used the range in the seventies. The tunnel was bricked-up at both ends for a distance of around 150yds. The range had space for 4 target shooters and targets could be positioned at intervals up to 100 yds.
I think the range closed due to dwindling membership in the Railway Club. There must literally be a ton or more of lead from spent bullets lying at the backstop at the end of that tunnel!
Hope this is of interest.