Civil engineer guide to fighting positions, shelters, obstacles

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AFH 10-222 Volume 14 1 August 2008 106 5.2.2.1. Reinforcing Berms. Berms can be used to provide additional strength to other barriers such as concrete structures. If an existing aboveground concrete wall can resist airblast loads but the wall thickness is not sufficient to prevent concrete spall from airblast and fragments, a soil berm placed against the wall is almost always the most economical way to prevent spall (Figure 5.8). Sandbags can be used to reinforce the berm’s face, especially if the berm is constructed of granular materials. Berms can also be built directly upon the structure they are intended to protect (Figure 5.9). In some cases (dictated by the threat), berms can be built upon a structure and continued over the top of the structure. Engineers with experience in structural analyses must make the determination on whether any structure can support additional loading from berming. Figure 5.8. Berm Supported by Revetments. Figure 5.9. Berm Supported by a Facility.
AFH 10-222 Volume 14 1 August 2008 107 5.2.2.2. Berms and Retaining Walls. If precast concrete revetments are not available for expediency, berms can be constructed against retaining walls if the proper materials are available. Building a berm against a retaining wall allows the berm to be located closer to the asset (Figure 5.10). Close placement provides a greater degree of protection from the effects of blast and fragmentation. Retaining walls should be no more than 11 feet high. Onesided retaining walls may also be built with 6- by 12-foot posts, 4- by 4-foot horizontal runners, and a sheathing surface of at least 1½ inches of plywood, heavier gauge (16 gauge or better) corrugated metal, or landing mats. Posts should be set at least 4 feet into the ground and no more than 4 feet apart. On the berm side of the posts, starting at ground level, nail horizontal runners to the posts at no more than 2 feet apart for each runner. Fill in between the 4- by 4-foot runners by nailing short sections of 4- by 4-foot pieces to the posts between runners. Fasten the plywood or metal sheathing to the 4 x 4s. There are two ways to anchor the retaining walls to each post. The more protected way is to anchor each post approximately two-thirds the height of the berm to deadman anchors that will be located under the berm material. Use at least 3/8-inch guy cable run on a 3:1 slope (vertical to horizontal) down to the deadman anchor. The alternative method is to anchor each post to three individual deadman anchors placed along the face of the berm. While this can help stabilize the berm, it exposes the anchors to more damage from blast. Figure 5.10. Berms Supported by Retaining Walls.
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