A good source of inspiration, go out and rent yourself some good old war films, there are a number of them that would be good sources. Saving Private Ryan, Platoon, The Logest Day, Band of Brothers, are just a few. Have you thought about what materials you will be using for the sandbags? Personally I have tried many ways this way can be frustrating at first but with some practice it works well. The best and most realistic by far is using a tube (to scale it escapes me at the moment as to what size I think it was about 3/8th), kleenex, VERY fine sand, and senic woodlands ground cover adhesive. Cut the kleenex into long strips, wrap it around the brass tube and glue the seam length wise and glue one end. Use a small funnel to pour the sand through filling the "bag" to a desired length tie off with very fine wire and then cut just above the wire. Repeat until you have the desired amount. When you are ready to create the sandbag pit, get a plastic bowl and mix your senics adhesive and your desired paint color together and dip the 'bags" in it with twezers taking care not to rip the 'bags" as they are very fragile when wet. Lay them on your base overlapping (like a brick wall)even rotating lengthwise as well. they should be at least two or three bags thick. Lay to the desired shape. When they are dry they will be rock hard, so as they dry poke with an xacto to create damage if desired. Dry brush highlights.