1, 2 Minimum Recommended

Armored steel 26.1 (663) 33.1 (840) Mild steel 32.6 (828.75) 41.3 (1050) Aluminum 45.7 (1160.25) 57.9 (1470) Lead 23.0 (583.44) 29.1 (739.2) Copper 24.5 (623.22) 31.1 (789.6) Concrete 47.5 (1206.66) 60.2 (1528.8) Earth 64.5 (1637.61) 81.7 (2074.8) Granite 43.9 (1113.84) 55.6 (1411.2) Rock 45.7 (1160.25) 57.9 (1470) Water 73.1 (1856.4) 92.6 (2352) Green wood 77.5 (1969.11) 98.2 (2494.8) Note.

Table was developed using information provided by Unified Facilities Criteria 3-340-01, the United States Army Research and Development Center, and the National Ground Intelligence Center. Calculations assume an RPG-7 with an 85-millimeter shaped charge warhead detonating in direct contact with protective material.

1

Thicknesses listed in the “Minimum” column provide protection against lethal injury, but may not protect against non-lethal injury. To achieve maximum protection for personnel, use thickness listed in the “Recommended” column.

2 _{The use of predetonation screens at an appropriate standoff distance can enable smaller thicknesses to provide the same}

level of protection. For assistance with determining appropriate predetonation screen designs and standoff distances, contact the United States Army Corps of Engineers Reachback Operations Center.

Legend:

Cover

Table 3-5. Material thickness (in inches) required to protect against indirect-fire fragmentation and blast exploding 50 feet away

Material Mortars 82 mm Mortars 120 mm Rockets 122 mm HE Shells 122 mm HE Shells 152 mm Bombs 100 lb Bombs 250 lb Bombs 500 lb Bombs 1,000 lb Solid walls Brick masonry 4 6 6 6 8 8 10 13 17 Concrete 4 5 5 5 6 8 10 15 18 Concrete, reinforced 3 4 4 4 5 7 9 12 15 Timber 8 12 12 12 14 15 18 24 30

Walls of loose material between boards

Brick rubble 9 12 12 12 12 18 24 28 30

Soil1 12 12 12 12 16 24 30 NR NR

Gravel, small stones

9 12 12 12 12 18 24 28 30

Sandbags filled with—

Brick rubble 10 18 18 18 20 20 20 30 40 Clay1 10 18 18 18 20 30 40 40 50 Gravel, small stones, soil 10 18 18 18 20 20 20 30 40 Sand1 8 16 16 16 18 30 30 40 40

Loose parapets of—

Clay1 12 20 20 20 30 36 48 60 NR Sand1 10 18 18 18 24 24 36 36 48 Snow Tamped 60 60 60 60 60 NR NR NR NR Unpacked 60 60 60 60 60 NR NR NR NR 1

Double the values if material is saturated.

Legend:

HE – high explosive lb – pound mm – millimeter NR – not recommended

3-39. Soil is often used for protection against the penetrating effects of projectiles. There are a few general rules about the ability of soil to protect against such penetration: coarse-grained and well-graded soils protect better than fine-grained soils; protection increases with the level of soil compaction; and protection decreases with increased soil moisture content.

3-40. Steel is a commonly used material to protect against penetration by projectiles and projectile fragments. Many field expedient types of steel can be used in construction, such as culvert sections, steel drums, and U-shaped pickets. Steel may be used for shielding, while steel structures such as culverts may be used as expedient protective shelters (when covered with soil or other protection). Containers express (CONEX) may also be used, both above- and belowground, as bunkers and protective positions. When using steel for shielding, the most effective application is to use plate steel. Place multiple members in contact with each other and add the thicknesses of the individual members until they meet or exceed the thicknesses in table 3-1, page 3-7. Ensure that the material is thick enough to defeat the threat that it is designed for. Steel used on the surface of a survivability position, that is not thick enough to defeat the threat, will provide an additional source of fragmentation that can kill or injure personnel.

3-41. Concrete is also very effective for shielding, but should not be used without steel reinforcement. A potential consequence of concrete penetration is spalling. If a projectile partially penetrates concrete shielding, particles and chunks of concrete often break or scab off the back of the shield at the time of impact. These particles can kill when broken loose, but they are commonly not lethal. The entries for concrete in table 3-1 include the thicknesses of concrete to prevent spall. Another option is to place sandbags up against the inner face of a wall that is not thick enough to prevent spall. The sandbags will

Chapter 3

3-12 ATP 3-37.34/MCWP 3-17.6 Publication Date

minimize the hazard associated with the spalling concrete. Other materials such as wood or steel can also be used to minimize spall effects. Concrete provides excellent protection against ionizing and thermal radiation. Prefabricated concrete barriers are used to protect structures against observation and attack and to provide standoff to mitigate the effects of explosive detonations. Prefabricated concrete structures are also commonly used as protective shelters in base camps and other contingency construction.

3-42. Rock, especially in layers, can protect against penetration by projectiles and projectile fragments. The more dense the rock properties, the better the protective qualities. Sandstone is less effective than basalt, shale, or gneiss. Rock is often used as a bursting layer in overhead cover.

3-43. Wood is often used for structural support in a survivability position. The low density and relatively low compressive strength of wood limits its ability to protect against penetration by projectiles and projectile fragments. Greater thicknesses of wood than of soil are needed for protection from penetration. The greater the thickness, the better the protection; but quantities are usually limited. Wood provides poor protection from ionizing and thermal radiation. Because of its low ignition point, wood is easily destroyed by fire from thermal radiation. In some areas of the world, wood construction materials are not readily available. Wood can also be subject to damage from pests.

3-44. Brick and masonry can be effective for shielding. They provide protection similar to that of concrete, but are less effective due to their lower compressive strengths. Generally, solid masonry or masonry with its voids filled with grout should be used for shielding against projectiles. Note also that masonry can exhibit spalling behavior similar to concrete as well; therefore, it should be treated similarly to concrete as discussed above. Ionizing and thermal radiation protection by brick and masonry are 1.5 times as effective as for soil. This characteristic is due to a higher compressive strength and hardness properties in brick and masonry. Since density determines the degree of protection against initial radiation, unreinforced brick and masonry are not as effective as concrete for penetration protection.

3-45. Sandbags can be used in a number of ways. They can be filled with soil, but should have minimal rock to minimize spalling when a sandbag is hit. There are also a number of techniques for quickly getting sandbags filled, such as the palletized load system’s concrete mobile chute and the small emplacement excavator attachment. Sandbagging is the least preferred soil construction method because it is the most costly in terms of materials and labor. If layers are not interlocked, sandbags will not be useful. Structures constructed of sandbags have a life of six months to a maximum of one year. The effects of sun and other weather considerations, and the type of sandbags used, will have an effect on their longevity.

3-46. One of the most common mistakes made in building sandbag structures is inadequate overhead support for the overhead sandbag cover. Ensure that such support is correctly designed. Figure 3-1 depicts an example of a poor sandbag technique: the sandbags are improperly filled, not interlocked and, therefore, do not form effective protection.

Cover 3-47. Figure 3-2 depicts a concrete shelter with sandbags being used to provide an additional level of protection. In this example, the sandbags are compact and properly supported by the bunker structure. The sandbags have been used to reduce the amount of fragmentation that can enter the bunker. As shown, the sandbags are interlocked, thus maximizing their overall effectiveness.

Figure 3-2. Proper sandbag technique example

3-48. Soil-filled containers are a common option for survivability construction. Soil-filled containers are easy to emplace, come in various sizes, are stackable to different heights, and may be used to protect existing structures or may be configured as a structure themselves. They typically come in multiple sizes that also allow for circumstances that require a taller soil-filled container, such as for aircraft revetments. Soil-filled containers consist of a fabric lined metal framework that interconnects and is then filled with soil. They may be used for walls and also for overhead protection, as long as the supporting structure is adequate. When building with soil-filled containers, ensure that the ground is level and well compacted, and that provisions are made for water to drain out of the enclosed area.