Electrical Resistivity Sounding has been in use since 1913 and went through major developments during the1980s. Since 1990 the electrical imaging technique has also undergone major development. The two techniques differ in their approach and are suited to investigating different geological situations. Both rely upon the variability in electrical resistivity exhibited by earth materials and utilise an array of four electrodes implanted into the ground surface.
The commonest two arrays are the Wenner and the Schlumberger configurations. Current is passed through the ground via the outer (‘C’) electrodes and potential difference is measured between the inner pair (‘P’). In the Wenner array the separation between each electrode (a) is equal. For the Schlumberger array, the distance between the two potential electrodes is small in comparison with that of the current electrodes. For the same current electrode separation, the Wenner array offers marginally improved resolution but a shallower depth of investigation over the Schlumberger array. For both array types, greater depth of investigation is achieved by increasing the separation of the current electrodes. The most common modern array is a modification of the Wenner, called the Offset Wenner. This is preferred as it improves data quality by being less sensitive to near-surface in-homogeneities.
Applications:
- Landfill Investigation
- Mapping and monitoring leachate plumes
- Mapping and monitoring of groundwater pollution
- Determination of depth to bedrock
- Locating sinkholes / cave systems
- Stratigraphic mapping
- Locating buried channels
- Mapping buried dykes and other ore bodies
- Locating fissures, faults and mine shafts
- Landslide assessments
- Buried foundation mapping
- Cross-borehole tomography
- Assessment of aquifer heterogeneity
- Soil corrosively assessment
