Soil Site Investigations Using 2D Resistivity Imaging Technique


The use of 2D Electrical Resistivity Imaging (ERI) technique in combination withgeotechnical and geological data allow the determination of the lithologicalcomposition and detailed internal architecture of the subsurface and understanding thecharacterisation and description of the geology of the site. This study is aimed toevaluate the use of 2D ERI for the detection and characterisation of heterogeneities insubsurface soil. The survey was conducted using a Wenner-Schlumberger and Wennerconfigurations along thirteen ERI parallel profiles which have been investigated in theproject of Al-Obaidi Electrical Transformation Station site to find the resistivity anddepth of soil horizons with their lithological description. Analysis of imaging sectionsshows that Wenner-Schlumberger sections are with higher resolving power thanWenner sections in both horizontal and vertical variations in resistivity reflecting morepronounced soil horizons with depth, where Wenner sections are limited to the uppersoil layers. Resisitvity values in the imaging sections indicate that the stratigraphy ofthe study area is mostly of clayey soil. 4 to 7 distinct geoelectric layers generallyidentify the subsurface down to depth of about 20 m. High resistivity values in the topsoil, medium-high resistivity values representing the upper soil layers, while lowerreistivity values are indicated for the lowerest layers. The resistivity values areinversely proportional to many soil properties such as fine content (clay and silt), saltcontent (sulphate and gypsum content) for saturated conditions, water content,plasticity index (P.I) and void ratio particularly for saturated condition. The resistivityvalues are directly proportional to sand content, void ratio, salt contents for drycondition. The integrated use of ERI technique and conventional site investigation hasled to a far better understanding of the site than could have been achieved using siteinvestigation methods alone.