Maybe some sort of earthen defense system? The straight and end sections remind me a bit of dykes/ levees.
If they're not home made, then maybe manufactured by someone like Scotia Grendel, Village Green (I think that's what the company was called anyways) or someone else that was allready selling terrain way back when a lot of the resin scenery/ terrain was a bit more brittle (and often a lot more funny smelling) than today.