The geotechnical properties of unconsolidated geo-materials such as
soils are influenced by modifications of their micro-structure, texture,
mineralogy, water content and imposed effective stress levels. Fundamental
relations between the characteristic electrical parameters describing the
electrical responses soils based on a fractal power law model with scaling
properties, and parameters influencing their geotechnical behavior are
investigated. Low frequency electrical conductivity laboratory measurements
were performed on sand and clay mixtures subjected to varying effective
stress levels with concurrent measurements of their geotechnical properties.
The conductivity spectra of the mixtures were described using a Jonscher
fractal power law model characterized with three characteristic parameters,
the dc conductivity ( σ dc ), the characteristic
frequency ( f c ) and an exponent ( n). Changes in
effective stress, water content, clay content, and other engineering
properties of the mixture such as dry density, porosity, pore size and
intergranular void ratio are discussed with respect to changes in the
electrical parameters. The dc conductivity and characteristic frequency
decrease with an increase in effective stress levels. The exponent, however,
has the opposite behavior and increases with an increase in effective
stress. As the water content increases, σ dc and f
c increase while n decreases for all mixtures. With
increasing stress levels, the average pore size of the mixtures decreases
which results in a decrease in σ dc and f
c but an increase in the values of the exponent. An
increase in dry density of the mixtures leads to a decrease in σ
dc and f c whilst n increases.
Both σ dc and f c increase with
increase in the intergranular void ratio of the mixture whilst the exponent
values decrease with an increase in the intergranular void ratio. This study
serves as a contribution to our quest in utilizing electrical geophysical
methods, to assess and monitor non-invasively, the geotechnical properties
of the subsurface in a less expensive and faster manner.
