Humboldt H-4114SD.3F Electrical Density Gauge - Manual (Page 9)

Soil Model Calibration Preparation
In order to use the Electrical Density Gauge (EDG) to determine moisture,
density and % compaction of materials, you must first develop what is called
a Soil Model of the material(s) you wish to ultimately measure. Per ASTM
D7698-11, a Soil Model is defined as: the result of a calibration procedure
that establishes a correlating linear function between measured electrical
soil properties and measured physical soil properties.
Part of this calibration procedure would be to obtain a representative
sample of soil from the Job Site where in-place testing will be conducted or
from the borrow area planned as a source of material. This sample should be
of a sufficient amount of soil for at least five compaction specimens, typically
about 20 Kg (44 lb) for material with a maximum particle size less than 5cm
(No. 4) sieve with a 5cm screen. More material may be required if ancillary
testing is planned, such as Atterberg Limits, particle size analysis, etc.
Determine the laboratory compaction characteristics of the material to be
tested. Test Methods D698 or D1557 for fine grained soils and soil rock
mixtures that exhibit a clear maximum dry density or Test Methods D4253
or D7382 for predominately granular material.
In many cases material selection for a particular project has already been
made and the necessary testing, i.e. the ASTM tests listed above, as well
as D2216 for determining moisture have already been completed. Results
from these tests should be used to determine a suitable area at the project
site to perform tests to develop a soil model, as well as what density and
moisture levels to use for the soil model evaluation. In order to be able to
determine % compaction readings for the material(s) when actual testing is
being conducted, proctor and moisture data from the above tests needs to
be entered into the gauge.
Producing a Soil Model
To develop an accurate soil model, it is suggested that you either use an
area of the Job Site where the material to be tested has already been
placed and compacted or a similar site, which has identical compacted
material in place.
To quantify readings made with the EDG while developing the soil model,
it is necessary to run a conventional method test (Nuclear Gauge, Sand
Cone, Voluvessel or Drive Tube and Moisture Tests) at the same time. If you
are going to use a nuclear gauge for this, it is recommended you still do
an alternate test for moisture, such as oven-dry, speedy or field burn off.
This correlates actual compaction and moisture numbers to the readings
obtained with the EDG, which provides the information the EDG needs to
make accurate determinations by itself. This regimen only needs to be
done to develop a Soil Model.
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