A few years ago I had the pleasure of spending several days chasing these bridges with Julia Page, who had a list of the successes and failures from, I think, an RE journal article.

The problems seemed to be quality of powder; damp powder; and inadequate equipment to prep the bridges because so much had been abandoned: at one bridge - I think As Nogais - the hole to take the charge was excavated with part of a camp kettle and wasn't deep enough to be effective, so it only took out some of the surface and the parapets to both sides.

hch