Misc. Reference Material - Bergey Tilt Tower Installation Manual

8) Misc. Reference Material

Anchoring
For most installation sites the 6" diameter expanding anchors supplied with the Tilt
Tower kits will be perfectly adequate. In some cases the soil will either be too weak for
proper strength or too "hard" for augering the hole. In these cases, a subsurface con-
crete pad can usually be substituted. In the case of hard rock, however, special rock
anchors may be necessary. This reference section is designed to provide you with con-
siderations and recommendations that will ensure that you install adequate anchors.
The installation of guy wire anchors is a critical element in the installation of the tower.
The anchoring system must be able to withstand, without appreciable creep, the steady
and vibratory loads of the guy wires through all weather conditions for the life of the in-
stallation. Site conditions will dictate the type of anchoring system used. Soil type, wa-
ter level, freeze depth, and weather variations all have an effect on the holding capacity
of the anchors.
Soil Types & Conditions
Most anchoring systems are designed to work in a limited range of soil conditions. To
choose the proper anchoring system, it must be possible to identify these various soils.
The accompanying Table 3 shows a system of soil classification developed by the A. B.
Chance Company on the basis of the mechanical properties of the soil.
The presence of water reduces the holding strength of the anchors. Anchor creep can
be a problem in soils with large variations in moisture content. If this condition can oc-
cur, it is best to ensure that the bearing surface of the anchor be placed below the level
of periodic surface saturation.
If an anchor is located above the depth to which the ground freezes, it may experience
a phenomenon known as "freeze-throw" or "jacking". This is the tendency of buried ob-
jects to be pushed toward the surface by the freeze-thaw cycles. To avoid this problem,
the bearing surface of the anchors must be placed below the level to which the ground
freezes. In areas of permafrost, the anchors should be below the permafrost line. Pro-
visions should be made to prevent solar energy from being transmitted down the rod. If
you must anchor within the permafrost zone we recommend using the services of a lo-
cal contractor with expertise in artic / cold climate anchoring.
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