Humboldt H-4114SD.3F Electrical Density Gauge - Manual (Page 18)

14. What you are trying to accomplish by building a soil model is to develop
a curve, which illustrates the density and moisture characteristics of the
material you wish to ultimately test. This curve will be comprised of a
series of tests (typically 6 to 12 tests) of the material at different levels
of compaction effort and different levels of moisture, which when
completed will produce a curve used by the EDG to provide accurate
readings of density and moisture.
To produce a Soil Model, traditional test methods (i.e. nuclear gauge,
sand cone, voluvessel or drive tube) are performed simultaneously on
the same location as each of the EDG tests you perform. This method
links the readings attained by the EDG to actual, density and moisture
readings attained from traditional methods. By using the EDG in
conjunction with a traditional method for providing density and moisture
readings, a curve is developed, which provides an accurate depiction of
the material's properties for varying density and moisture readings. It is
this curve, which allows the EDG to then produce accurate readings in
subsequent testing of this specific material.
15. You are now ready to proceed with the actual Soil Model development.
If you are not already at the test site, proceed there. The test site can
either be the actual project site you desire to test or a site that uses the
same material you will be using at your project site.
When doing your Soil Model, you should use a Dart Length that
coincides with the expected lift height, which will be used for the
project. Darts are available in the following lengths: 4" (10.2cm); 6"
(15.2cm); 8" (20.3cm); 10" (25.4cm), and 12" (30.5cm).
Select areas on the Job Site where the type of soil is consistent from
place to place, and where there are differences in water content and
compaction. Special preparation of spots of different densities or water
contents should be done the day before, so as to allow stabilization of
the soil water content.
A matrix of six (6) spots should be used during the calibration proce-
dure, which consists of two different soil density conditions and three (3)
water content conditions that cover the range that is expected to be
measured. The three calibration tests that evaluate high density soil
will use test locations that ideally will have soil conditions that are close
to the maximum density as determined by Test Methods D1557 or an
equivalent method. The range in water content should include low water
content, middle range water content, and high water content that is
near the optimum water content as determined by Test Methods D1557
and D2216 or equivalent test methods.
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