Everything Needs Maintenance...

But maintenance needs to be handled correctly. Design limits have to be respected. Parapet collapse ‘may have been caused by weight of ballast’ as bridge repairs to take another three weeks

Railway ballast is the crushed rock that holds railroad ties in place. It needs to be cleaned and regraded from time to time, as dirt can interfere with drainage, and the track has to be kept level. Sometimes new ballast must be added, but you cannot ignore weight limits on bridges.

A portion of a parapet (side wall) of a 180-year-old railway bridge in Scotland collapsed, stopping freight and commuter traffic on the line. It is expected that the collapse was in part due to excess weight from added ballast. The line in question will be closed at least until February 22nd.

Industry commentator Philip Haigh, writing in RAIL magazine, he said: “Over the years, the track engineer had dropped more and more ballast to keep the track level.

"It might be that this increased burden of ballast has increased pressure on parapets not designed for such a load.

If it that turns out be the case, then the railway has a lot of work to do, as there are any number of similar bridges, probably also overloaded with ballast.

"After three or four passes of this type of maintenance, the ballast is supposed to be renewed and the track level reset to its original position.

There are a lot of fascinating videos of railway maintenance machines. It has to be done regularly. Down time for maintenance is expensive. And so there are a lot of fairly fascinating machines that pull up track, pull up ties, collect and clean ballast, reset ties, bury with ballast and tamp, etc. Here is one such video, though it is a bit long at 7 minutes.

Everything needs maintenance. But you cannot congratulate yourself for maintaining your infrastructure and ignore the engineering limits of that infrastructure while you do. Sadly, this kind of thing isn't completely unheard of. The I-35 bridge collapse in Minneapolis in 2007 was apparently caused (in part) when a construction company getting ready to do maintenance placed materials and machines on the bridge that exceeded the designed weight limit by four times.

Engineering is hard. But necessary.

I tried to find an image of the impacted causeway that's in the Public Domain without any luck. The stock aerial photo of the collapse isn't very good, but you can find it as the article linked at the top of this post.