Passive Barriers. Use passive barriers where unmovable
barriers are needed, such as along a perimeter chain-link fence.
Active Barriers. Use active barriers where vehicles must be
allowed passage, but the capacity to stop them must also be maintained.
Reinforcement of Perimeter Chain-Link Fence. A reasonable
approach to reinforce a standard chain-link perimeter fence to resist a
vehicle attack is both simple and aesthetic. Place a 3/4-inch (19.1-mm)
diameter aircraft cable, conforming to MIL-W-83420, along the fence line,
between the fence posts and the chain-link fabric as shown in Figure 10.
Fasten the cable with 1/2-inch (12.7-mm) U-clamps (SAE Grade 3 or better) at a
height of approximately 30 inches (762 mm) from ground level. Terminate each
cable end with either three wire rope clamps (MS16842) or a wire rope
hydraulically swaged press fitting (MIL-P-80104). The cable end will be
attached to one end of a 3/4-inch (19.1-mm) round turnbuckle (MS51561) with
double eye ends which in turn will be attached to the deadman eyebolt (MIL-B-
45908) by a 3/4-inch (19.1-mm) anchor shackle (SAE Grade 8 or ASTM A 490).
The deadman anchor will be a concrete cube, approximately 3 by 3
by 3 feet (1 by 1 by 1 m). Eyebolts captured in the deadman anchors will have
either a welded "T" or "L" end embedded in the concrete as shown in Figure 11.
As a minimum, 2 feet (0.610 mm) of the eyebolt and its welded extension will
be captured within the concrete of the deadman. The shaft of the eyebolt will
be either in-line with the attached cable or the eye of the eyebolt will be
flush with the surface of the deadman. Anchors shall be placed at a minimum
of 200-foot (60.9-m) intervals and a maximum of 1,000-foot (304.8-m) intervals
on the inside of the perimeter fence with the front edge of the deadman flush
with the fence fabric. The top of the deadman will be either flush or buried
below the surface as long as the eye of the eyebolt is above ground level.
Cables must overlap as shown in Figure 10 before terminating at a deadman so
that no voids in the cable occur along the perimeter. If additional hardening
is desired, a second cable should be placed about 5 inches (127 mm) above the
first cable and attached as described above. It may be anchored to the same
deadmen used by the first cable system.
When gates form a portion of the fence line being protected by a
vehicle restraint cable system, then the gate cable system described in
Section 3 must be interconnected to the fence cable system to ensure
continuity of the cable system. Often, natural barriers such as mountains,
cliffs, rivers, seas, trees, vegetation, or other terrain protect the fence
from vehicle attack. The vehicle restraint cable system should not be used
along portions of the fence line that are otherwise protected by natural
barriers, such as large boulders, trees, natural ravines, and ditches.