This is the same building as the unlinteled door – it was chock full of bad masonry conditions. The picture above is just to provide some context. I’m interested in the brick pier in the cellar. Here it is in isolation:
There are several possible causes for the visible damage, but rising damp is the one that best fits the evidence. The cellar of a house is not somewhere you’d expect moving equipment that could lead to the impacts necessary to damage brick after brick; the site is on a hill with good drainage, so it’s unlikely that the cellar has flooded regularly.
The fact that the mortar is more or less intact while the bricks are turning back into clay and collapsing is good evidence that the mortar is portland-cement based. Deterioration of the building has opened up the cellar to the exterior air, which actually speeds up the deterioration: rising damp in a humid cellar is inhibited by the water vapor in the air. Rising damp moves faster in an area at ambient humidity, which is almost always less than that of an unventilated cellar.
Unoccupied buildings are more vulnerable to structural damage than buildings in use because there’s no one to complain about the first signs of trouble – leaks, jamming doors, warping floor boards, and so on – and because they no longer have ordinary heating cycles. Buildings that have had partial demolition (including finishes) or partial failure are much more vulnerable. The ordinary flow of water and air through the building is increased, the building is more flexible than it was before and therefore likely to develop new cracks in its exterior, the new load paths created by removal or old load paths may overload areas that were previously okay. This last item is of course the essence of progressive failure.
That’s a lot to pin on one pier with failing brick, but collapses have to start somewhere.