Tactical Facility Construction 8 February 2009 FM 3-05.230 3-9 BRICK AND MASONRY 3-24. Brick and masonry (Figure 3-5) provide excellent building materials, simplifying the precise construction of buildings and fighting positions. Direct and indirect fire fragmentation penetration into brick and masonry has the same protection limitations as rock. Figure 3-5. Brick slab roofing WOOD 3-25. Direct and indirect fire fragmentation protection using wood is limited because of its low density and relatively low compressive strengths. Wood is generally used as structural support for bunkers and buildings. Wood is less effective than soil for protection against penetration, and, with its low ignition point, it is easily destroyed by fire. In a tropical climate, wood is subject to weather extremes, animals, birds, insects, and harmful fungus that degrades wood in short order. 3-26. Building a roof using native hardwoods (at least 6 inches in diameter), the SF unit installs two layers of logs as a roof. The second log layer is installed perpendicular to the first, and both layers provide an overhang of 12 to 24 inches. Layers of sandbags and corrugated sheeting may be positioned between and above the log layers to help absorb mortar blasts. Because the level of protection afforded by these layers results in a sizeable increase in roof weight, more and larger vertical supports will be required. SANDBAGS 3-27. The walls of buildings and fighting positions are built of sandbags in much the same way bricks are used; however, they should be used only to protect—not to support—the roof. When building with sandbags, a minimum depth of two layers is used. Sandbags also are useful for retaining-wall revetments. Most sandbags are made of an acrylic fabric that is rot and weather resistant. In most climates, plastic-
Chapter 3 3-10 FM 3-05.230 8 February 2009 based sandbags have a lifespan of 2 years with minimal deterioration. Older style burlap-based bags deteriorate much more quickly, particularly in tropical climates. The useful life of sandbags may be prolonged by filling them with a mixture of dry earth and cement, normally in the ratio of 1 part cement to 10 parts dry earth. The cement sets as the bags take on moisture. For sand and gravel mixtures, a 1 to 6 ratio is used. Filled bags may also be dipped and coated in cement-water slurry. Each sandbag is then pounded with a flat object, such as a section of lumber, to make retaining walls more stable. 3-28. Sandbags can be used for revetting walls or repairing trenches when the soil is very loose and requires a retaining wall. A sandbag revetment will not remain standing if it has a vertical face. The sandbag face must have a slope ratio of 1 to 4 toward the top of the wall—leaning against the bare earth it holds in place. The base for the sandbag revetment must stand on firm ground. To construct a sandbag revetment wall, the SF unit— z Fills sandbags about three-quarters full with earth or a dry soil-cement mixture, ties the choke cords, and tucks the bottom corners of the bags after filling.
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- Spring '19
- John Foe
- United States Army, Special Activities Division, Special forces, John F. Kennedy Special Warfare Center and School, Special Forces Tactical Facility