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Civil engineer guide to fighting positions, shelters, obstacles

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AFH 10-222 Volume 14 1 August 2008 29<br />

2.5.1.6. Crawl Trenches. If time is available and the overall defensive posture<br />

needs <strong>to</strong> be enhanced, crawl trenches can be constructed <strong>to</strong> connect <strong>fighting</strong><br />

<strong>positions</strong> and prevent personnel from being exposed <strong>to</strong> enemy fire as they<br />

move about the area. The depth of these trenches is based on the availability<br />

of time and resources. Engineers will have <strong>to</strong> assist others with excavation<br />

and trench reinforcement (Figure 2.6). Crawl trenches should be dug in a<br />

zigzagged pattern <strong>to</strong> prevent the enemy from being able <strong>to</strong> fire down a long<br />

section if the trench is breached. This pattern will also help <strong>to</strong> reduce the effects<br />

of fragmentation if the crawl trench is hit with explosive munitions.<br />

2.5.1.7. Ground Shock Intercept Trenches. Since <strong>fighting</strong> <strong>positions</strong> might<br />

be needed in areas subject <strong>to</strong> high levels of ground shock based on certain<br />

soil or geological conditions, civil <strong>engineer</strong>s must have some general knowledge<br />

of geology and different soil types. Ground shock sufficient enough <strong>to</strong><br />

collapse <strong>fighting</strong> <strong>positions</strong> can occur when these <strong>positions</strong> are constructed<br />

over water tables <strong>to</strong>o close <strong>to</strong> the bot<strong>to</strong>m of the <strong>positions</strong> or in areas where the<br />

soil is located within 25 feet of and/or over an underlying rock formation,<br />

moist clay, or soils with high water content. Ground shock is intensified by<br />

reduced resistance through the soil or reflection from the underlying soil and<br />

rock formations. One way <strong>to</strong> reduce the effect of ground shock on <strong>fighting</strong><br />

<strong>positions</strong> involves constructing ground shock intercept trenches. Ground<br />

shock intercept trenches are meant <strong>to</strong> collapse from ground shock and thereby<br />

absorb enough of the ground shock <strong>to</strong> prevent <strong>fighting</strong> <strong>positions</strong> from collapsing.<br />

These types of trenches are dug approximately 12 inches wide <strong>to</strong> a depth<br />

that is at least 2 feet deeper than the <strong>fighting</strong> <strong>positions</strong> they are intended <strong>to</strong><br />

protect. They should also be at least 6 feet longer than the width of the <strong>fighting</strong><br />

position. Locate the trenches away from <strong>fighting</strong> <strong>positions</strong> at a distance<br />

approximately 1 1/2 <strong>to</strong> 2 times the depth of the trench, as illustrated in Figure<br />

2.7. Due <strong>to</strong> their narrow width, these trenches can easily be camouflaged.<br />

Table 2.2 can be used as a checklist <strong>to</strong> ensure revetments, crawl trenches, and<br />

ground shock intercept trenches are being properly constructed.

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