United States Department of Transportation
i
Rapid field detection of sulfate and organic content in soils : technical report.
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2011-06-01
[PDF-4.93 MB]
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Edition:Technical report; Sept. 2009-Aug. 2010.
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Abstract:In recent years, the Texas Department of Transportation (TxDOT) has experienced problems chemically
stabilizing moderate to high plasticity clay soils with calcium-based additives. Many of the problems are the
result of soluble sulfate minerals in the soil reacting with the lime or cement added for stabilization. The
occurrence of these deposits is unpredictable and often restricted to small areas. To address this problem,
the researchers set about identifying a technique that provides a map showing the sulfate content of the soil
over a large area to a depth of 3 to 4 ft. Two technologies were identified that provide an indirect
measurement of sulfate salts (an electromagnetic device – EM-38, and a soil conductivity device – VERIS
3150). We tested these devices on three different TxDOT projects in different parts of the state that have
been known for high sulfate contents. We collected soil samples at 1 ft intervals to a depth of 4 ft where the
data varied. We measured the PI, moisture content, sulfate content, and organic content in each sample. We
then ran multivariate statistical analyses to correlate the conductivity data collected with the VERIS 3150 to
laboratory-measured soil properties. We observed that soil conductivity is related to the soil texture/clay
content, moisture content, and dissolved salts (i.e., sulfate and other salt minerals). We noted that for all of
the projects tested, a soil conductivity over 100 mS/m may contain problematic sulfate levels, but it may also
be due to high plasticity clay soils and/or high moisture contents with other dissolved salts. What is
noteworthy about this research is it provides a tool to intelligently decide where to collect soil samples to
analyze for problematic sulfate levels versus the current method of collecting soil samples in a grid pattern of
a specified interval that may be too large and not detect problematic sulfate levels until the road explodes.
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