Since warfare as we know it has existed earthen fortifications have been employed defensively in one form or other. Over time thick mounds of hardened mud and clay gave way to ramparts held down with rocks and dirt. These ramparts became sandbag bunkers and pillboxes. Such bunkers are still in use today by many national militaries as relatively quick and cheap barracks for soldiers as well as protected weapon emplacements. Thick bags of sand can just as easily stop a speeding bullet as a thick plate of steel, and are much cheaper to construct. They provide good protection from the heat of the day and can be easily warmed with a little ingenuity. A military sandbag bunker might look a little odd out in your front yard. However battle re-creationists and paintball players could benefit from their creation and use. Such a bunker would also make an excellent lodge if you spend much time hunting out in the woods. To that end, here is a guide on how to build your own sandbag bunker.
Lay the wooden stakes down in a rough outline in the shape of the bunker's walls. Flat ground will be easier to work on.
Prepare the ground by using your shovel to dig out all the plants and grass inside the bunker.
Start digging. Use the earth you take from inside the outline of your bunker to fill the empty sandbags. Each bag will typically weight 50 pounds when full. They come with ties and drawstrings to close them up once you're ready to place them. Dig from the outside edges of the bunker inward. That way you can get the filled sandbags in place as soon as possible. Still, this part of the construction may take weeks depending on how big the finished bunker will be and how many people you have to help you.
Place the filled bags long-end to long-end in two rows side-by-side in the shape of the bunker's walls just outside the stakes. This will allow you to take advantage of the height difference you're creating. If you hollow out the ground inside the bunker three feet deep, then you only have to pile the sandbags four feet high to have a seven foot high space for people to comfortably move around in.
Put the second layer of sand bags crosswise over the first layer. Keep doing this for each successive layer. This will add a great deal of stability to the walls. They're much less likely to tip over this way.
Hammer the stakes in to support the inside wall of the bunker. You should have at least one stake for every two feet of wall. For a relatively small bunker, sharpened 2X4s will work, but a large bunker will have a great deal more sand leaning inward on it and it would be a good idea to use 4X4s. The stakes should be driven in vertically and stand slightly above the very top layer of sandbags. When placing sandbags make sure they're snug against the stakes.
Place the flak or duck-board planks over the top of the bunker when the walls are the desired height. Nail these boards firmly to the tops of the stakes.
Place a single layer of sandbags over the boards. When you finish, the duck-boards shouldn't be visible at all because of the sandbags covering them. Make absolutely sure that your stakes can take the weight. If you see the boards bowing near the center of the roof or hear the wood groaning then immediately place more stakes closer to the center of the bunker to help support the weight of the sandbags.