The use of 2D Electrical Resistivity Imaging (ERI) technique in combination with
geotechnical and geological data allow the determination of the lithological
composition and detailed internal architecture of the subsurface and understanding the
characterisation and description of the geology of the site. This study is aimed to
evaluate the use of 2D ERI for the detection and characterisation of heterogeneities in
subsurface soil. The survey was conducted using a Wenner-Schlumberger and Wenner
configurations along thirteen ERI parallel profiles which have been investigated in the
project of Al-Obaidi Electrical Transformation Station site to find the resistivity and
depth of soil horizons with their lithological description. Analysis of imaging sections
shows that Wenner-Schlumberger sections are with higher resolving power than
Wenner sections in both horizontal and vertical variations in resistivity reflecting more
pronounced soil horizons with depth, where Wenner sections are limited to the upper
soil layers. Resisitvity values in the imaging sections indicate that the stratigraphy of
the study area is mostly of clayey soil. 4 to 7 distinct geoelectric layers generally
identify the subsurface down to depth of about 20 m. High resistivity values in the top
soil, medium-high resistivity values representing the upper soil layers, while lower
reistivity values are indicated for the lowerest layers. The resistivity values are
inversely proportional to many soil properties such as fine content (clay and silt), salt
content (sulphate and gypsum content) for saturated conditions, water content,
plasticity index (P.I) and void ratio particularly for saturated condition. The resistivity
values are directly proportional to sand content, void ratio, salt contents for dry
condition. The integrated use of ERI technique and conventional site investigation has
led to a far better understanding of the site than could have been achieved using site
investigation methods alone.