Looks like the work of muppets to me.
most of the welded plates were still on last time I was there too.
Only thing of real interest in there is the ventilation fan and bypass door from later working beneath this level.
Been in there a few times, the 1st collapse was negotiable and most of the 2nd one too although it means crawling through the shale void above the roof timbers then dropping back down into the main way, very hard going and unrewarding.
Shame some idiot had to vandalise that doorway