Found this on French railway magazine website. A new book due in October
Les chemins de fer français dans la première guerre mondiale
http://www.lrmodelisme.com/librairie/1690-les-chemins-de-fer-francais-dans-la-premiere-guerre-mondiale.html#menu_centre
Mainly interested in narrow gauge railways, currently working a number of WW1 projects in 1/35 scale , website http://www.rue-d-etropal.com/
Simon