| Summary: | The piezocone (CPTU) is a commonly used instrument to assess
soil parameters and soil type in geotechnical investigations.
However, it is sometimes difficult to distinguish between two
soil types that are only subtly different such as fine sand and
silty sand with the CPTU. In these cases an alternate method
of determining soil type may be required. In order to assess
soil type, we may measure the fines content of the soil. One
method of assessing fines content within a soil is to measure
the natural gamma radiation decay for the common clay mineral
constituents potassium and thorium. A gamma logging module has
been developed that fits the aforementioned cone penetrometer
and records natural gamma data while the CPTU is performed.
This test has been labelled the Gamma Cone Penetration
Test(GCPT). Since emitted gamma radiation increases with
increasing fines content, the instrument can be used to
qualitatively distinguish soil type and fines content based on
local correlations.
Another application of the GCPT is for the measurement of insitu
soil density. The back scatter from a module containing a small
Cesium source mounted below the GCPT can be correlated to soil
density. The GCPT also has environmental applications. It can be used
locate radioactive contamination based on a gross gamma count
log. Once the contamination is located, the GCPT can measure
the gamma energy spectrum in order to identify the radioactive
isotope. Since the GCPT is a penetration tool, there are no
drill cuttings brought to the surface and worker exposure to
potentially hazardous radiation is minimized.
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