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Published By Lankelma

Lankelma is the foremost contractor for onshore in-situ soil testing in the UK. An acknowledged specialist in CPT, Lankelma also offers a worldwide consultancy and training service.

A.P. van den Berg develops, designs and manufactures geotechnical and environmental soil investigation equipment for onshore and offshore applications. Specialists in CPT systems and equipment.


Gardline Geosciences offers worldwide marine geotechnics, in-house consutancy and services with marine investigations ranging from nearshore to full ocean depth (down to 3000m).

About the Author

Hans Brouwer studied civil engineering at Delft University in The Netherlands. He has worked as a part-time lecturer at Amsterdam Polytechnic and was senior partner in a structural engineering consultancy. He has written a standard textbook in Dutch about the design of building foundations. He now lives in England where he writes technical textbooks in English, hopefully to reach a bigger readership.

Chapter 4

Part 1: Special cones: geotechnical cones

Soil moisture probe (SMP)

        SOIL MOISTURE PROBE (SMP)    4.7
The soil moisture probe (SMP) is installed directly behind the electric cone and permits the simultaneous acquisition of resistivity, soil moisture and geotechnical data (Figure 25). The probe comprises two ring-shaped and carefully isolated electrodes, and an application-specific integrated circuit (ASIC). The ASIC uses synchronous detection for accurate measurements free from electric interference.
Soil moisture
Dielectric soil properties, capacitance
and electrical conductivity are governed
mainly by the water content of the soil
mass. By measuring these parameters
between two electrodes, with the soil
dielectric in between, the soil moisture
can be determined. 
The capacitance of dry soil is determined by its dielectric constant. For
dry soil this constant is of the order of 3 to 6 and for water the constant
is 80; in other words, the capacitance between the two electrodes is
dominated by the volume fraction of water.
Contaminated soils
In polluted soils, non-aqueous phase liquids (NAPLs, eg oil or
chlorinated solvents) will replace part of the water in the soil matrix. As
they do not dissolve easily in groundwater, they will occur as a film of
pure product, often just above the groundwater table.
Dense NAPLs such as chlorinated hydrocarbons, which are denser than
water, will penetrate the groundwater table and are typically found on
top of impermeable layers. These pollutants affect the dielectric
properties of the soil significantly and are detectable using the soil
moisture probe.
Test results are shown in Figure 26 below. 
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