Yes, good picture, the sleepers/ties look rather light (but closely spaced), I'm sure an expert could work out a lot from this depiction.
I think it would be found that Le génie militaire actually operated, extended, inspected and maintained the military rail system (more than guarding it) during wartime. Certainly that was the case with British forces (rail operations an RE function, not ASC). But I'm not sure about the French and, anyway, in 1914 I guess they were mostly securing existing civilian lines (mostly standard gauge), inspecting and maintaining them.
"Railpower" (in the same sense as "Seapower") was of enormous strategic importance, to an extent easily overlooked these days but the object of great attention from the mid 19th century to early 20th century.
Several years ago a French Engineer proposed a new kind of railtrack with a wider pitch (I believe that was 2 metres) for more stability. Given all the recent de-railments I wondered if that was an idea for considering for Goods transport.
