I've been down similar tunnels in Whiteinch / Scotstoun probably about 15 years ago - I think the ones on the orignal post are along south st closer to the JOrdanvale Ind Estate / towards the Granary.
The ones I was down were in what is now the WH Malcolm Yard between Barclay Curle & First Bus - it used to be occupied by Corus Distribution.
Basically they were service tunnels (roughly 6ft by 6ft although it got narrower in places) with all sorts of electrical trunking/cabinets - i was told they were used to power the huge dockside cranes that used to operate on the quayside when it was a ship yard (the slipways are still in existance), we went down one night shift and spent a good 30 mins walking from one end to the other exploring and dodging several very large rats.
The tunnel was about 3 or 4 meters from the quay wall under with about 3ft of heavily reinforced concrete above your head - there was no openings on they quay wall probably to prevent flooding of cables.
I can confirm that all the electrical gubbins / cabling was removed before Corus moved out about 5 years ago now, and I think the access door was sealed permantly.