Civil engineer guide to fighting positions, shelters, obstacles

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AFH 10-222 Volume 14 1 August 2008 118 5.8. Concrete Culverts. Precast concrete culverts are constructed in various sizes, but are usually limited to 8-foot lengths for ease of handling. If the concrete culvert’s outside diameter is at least 30 inches, it can be used for protective construction. Larger diameter culverts (up to 6 feet in diameter) can also be used. The culverts are stood up on end to stabilize the foundation and positioned closely together. If possible, obtain straight-sided culverts (without grooved ends) so they can be placed together vertically without any gaps between them. If the culverts have bell ends, place the larger bell ends down and fill in the gaps between rows with filled, smaller diameter PVC pipe or concrete culverts. Use at least two rows of culverts, and stagger the joints as indicated in Figure 5.21. If available, drive steel dowels or pipes into the ground at the center of each pipe to stabilize them. Fill the culverts with dry sand or soil and cap the tops with at least 10 inches of concrete and a short length of exposed dowel or pipe. Tie the dowels together by welding reinforcing bars to the dowels on each row and between the opposite two adjoining culverts. Do not stack culverts on top of each other. Be aware that concrete culverts come in various strengths to resist traffic loads. Culverts with little traffic loading capacity are usually constructed with lower quality concrete and less reinforcing, making them unsuitable for use. Figure 5.21. Concrete Culvert Soil Bin.
AFH 10-222 Volume 14 1 August 2008 119 5.9. Timber and Lumber Revetments. There is little difference between timber and lumber revetments except the raw materials. They are both built like plywood walls, except that the inside facing material is either saplings or lumber (Figure 5.22). The facing timbers of the timber revetment are usually 2- to 3-inch sapling trunks laid parallel, one on top of the other and fitted together to avoid gaps. The facing lumber of a lumber revetment is a minimum 2-inch thick board or 2 inches of layered plywood sheathing. For a timber revetment, the posts are usually 6 inches in diameter and spaced no more than 2 feet apart, while lumber revetments use 2- by 4-inch studs spaced about 12 inches apart. The posts are normally set 2 feet into the ground for bracing and have 3 tie-cables run between opposite posts. One cable provides a tie at midheight, while the other two cables are at about 1/6 the height from the top and the bottom, respectively. As a minimum, every other post is tied. The ends of the revetments are blocked with additional posts of timber or lumber; therefore, the minimum width of the revetment can be greater than the plywood wall type revetment. As a minimum, the walls are built in cells every 10 feet. A cross-braced wall is built within the lumber revetment by using 2 sets of 4- by 4-inch posts set 2 inches apart to create a slot on the inside of each wall. Then 2-inch thick lumber is stacked in the slot to create a cross-braced wall section. For the timber wall, two sets of the 6-inch diameter posts are set about 3 inches apart on each side of the wall. Cross members are notched and stacked to fit into the facing logs. Timber and lumber revetments are filled with soil to provide strength and stability for these expedient structures. Figure 5.22. Timber and Lumber Revetments.
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Civil engineer guide to fighting positions, shelters, obstacles

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