Etymology of chandelier as relating to fortifications
Solution 1:
The OED confirms that 'chandelier', in its usual sense, is of modern etymology, precisely from the French.
But the only alternative meaning it gives is the one below, which is not quite the same thing to which you refer. But if anyone has access to Stocqueler (Military Encyclopaedia) it may tell us. Perhaps the 'sappers' traverse doubled for use in supporting fences when the sapping was done.
Mil. ‘A wooden frame, which was filled with fascines, to form a traverse in sapping’ (Stocqueler Mil. Encycl.), and cover the sappers.