The solution presupposes the railway even has the first clue which bits of it are vulnerable to this kind of settlement, where the long term absence of water is a factor, and which bits where the sustained application of even small amounts of water, if done over long enough periods, could have similarly disasterous effects.
I was quite struck by the fact the engineers who upgraded the Ashington freight line to passenger service, apparently had no clue that the embankments on the line were formed from ash from old mine workings. As a result, presumably with a mind to modern engineering standards, they had to do a lot more work than they had previously thought necessary, to ensure the embankment was stable enough for a double track.
You would think that kind of thing would be documented somewhere, as part of some nationwide land survey of the permanent way, let alone be common knowledge among the railway engineering sector. But evidently not.
I'm no expert, but running a rehydrarion train for weeks on end, over an embankment formed of ash, would not be advisable. I have been told by structural engineers that even a tiny crack in a toilet soil pipe, given the frequency and volumes of the typical household toilet, would far exceed the amount of water expected in rainfal, and thus, eventually, cause settlement in the foundation. And that's in ordinary soil, not ash.
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