This steelwork looks like Hollybank type roof supports, different from usual systems using fishplates by having a single bolt joint arrangement. Often used in coal mining, especially in retreat systems & advance headings, where removal of the support leg was "easier", detail shown here:
🔗Personal-Album-5532-Image-51206[linkphoto]Personal-Album-5532-Image-51206[/linkphoto][/link]
Photograph:
🔗Watersaw-Fluorite-Mine-User-Album-Image-011[linkphoto]Watersaw-Fluorite-Mine-User-Album-Image-011[/linkphoto][/link]
'where's the shearer?'[center]