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Direct transmission wet density will not be affected by a trench
wall or vertical structure. Moisture and dry density (WD-M)
may be affected when a gauge is operated within 0.6 meters (24
inches) of a large vertical structure with a moisture content of
240 kg/m
3
(15 pcf) or greater.
Fore trenches with a width of one meter (40 inches) or more,
the moisture error will be less than 24 kg/m
3
(1.5 pcf) when the
measurement is performed in the center of the trench.
Correction Procedure
1. Obtain the daily standard counts following the steps outline
on page 3-2. (If a valid set of standard counts has already
been obtained, it may be used.) Note that the standard
counts are taken at a site away from the trench.
2. Enter the trench and take a set of counts (not a standard
count) with the gauge placed on the reference standard at the
desired test site. The distance from the wall must be the
same as the area to be tested. This count may be taken with
the PWR/TIME switch set on NORM. On the 3411, do not
press 〈SHIFT〉 because your standard count will be erased.
3. Determine the moisture offset value by subtracting the
moisture standard count from the second moisture count
obtained in the trench. Record this number for future tests
performed at this site and with this gauge at the same
distance from the wall.
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