Geoelectric imaging is one of the most versatile and successful geophysical prospecting methods for groundwater prospecting, mineral prospecting, ground resistance measurements, geological and geotechnical mapping, bedrock studies, specific civil engineering applications. Electrical imaging is a popular method because of its low cost, simple operation, and efficient ability to distinguish between weathered overburden and compact bedrock by resistivity contrast. Electrical resistivity surveying methods have been widely used to determine layered mediums' thickness and resistivity 1for groundwater and mineral exploration. Traditionally, vertical electrical soundings are applied to a horizontally or near to horizontally layered surface on earth to interpret subsurface geological formation interns of resistivity values such as sedimentary rocks of different lithologies, layered aquifers of different properties, sedimentary rocks overlying igneous, or weathering zone of igneous rocks. The electrical resistivity method is a useful geophysical tool that is widely used for groundwater exploration ( Olayinka, 1991; Ndlovu et al., 2010; Metwaly et al., 2009). It provides information about the near-surface structures. The Electrical Resistivity method is used to provide reliable information about the subsurface layers. Vertical electrical sounding (VES) can also be used to determine the aquifer depth, aquifer geometry hydraulic conductivity, the water quality of the aquifer rock, and geological stratigraphy are reported by researchers (Chandra et al., 2008). In this paper, an attempt has been made to assess subsurface heterogeneities using GD-10 MultiElectrode Resistivity Imaging System and CRM-500 Resistivity meter
A systematic field survey has been carried out to collect data using the GD-10 Multi-Electrode Resistivity Imaging System and Aquameter CRM-500 Resistivity meter at open space of NIT Raipur campus during September 2020-October 2020 (Fig. 2)
Fig. 2: Field survey photographs.
GD-10 Multi-Electrode Resistivity Imaging System
GD-10 is developed based on the latest digital and analog circuitry technique, making it the worldleading multi-functional direct current (DC) method instrument. GD-10 Multi-Electrode Resistivity Imaging System is capable of conducting 2D/3D cross-section profiling of subsurface lithology. through the array script management in Geomative Studio, we can predefine survey parameters prior to field surveys. Up to 3200W (800V*4A) transmission power can be deployed in the field. GD-10 is equipped with both centralized cabling and distributed cabling system to fulfill any complex field environment
Aquameter CRM 500 Resistivity Meter
CRM 500 generates a well-regulated current (I) measure the resulting signals voltage ΔV between the two potential electrodes. It then calculates the apparent resistivity R= ΔV/I for the given spacing configuration. The resistivity obtained is the weighted average of all the formations' resistivity through which the current is passing. Apparent resistivity is expressed in Ohm-meter(Ω-m). The analysis of apparent resistivity variations as a function of current electrodes' spacing makes it possible to conclude subsurface geological conditions.
In this study, one horizontal profiling using GD-10 Multi-Electrode Resistivity Imaging System was carried out to assess the subsurface geological heterogeneity. Vertical Electrical Sounding (VES) using the Schlumberger method of maximum current electrodes spacing of 300 m using Aquameter CRM 500 Resistivity Meter.
The layer parameters are obtained from the recorded field resistivity data using Res2DInv Aarhus GeoSoftware for Multi-Electrode Resistivity Imaging System and the resistivity meter1-D sounding inversion program IX1D v3 software used to assess the subsurface geological heterogeneity are obtained from the recorded field resistivity data (VES)
Fig. 3: 2D Subsurface heterogeneity in the NIT Raipur campus.
Fig. 4: 1D Subsurface heterogeneity in the NIT Raipur campus.
We have conducted geoelectric imaging using the Wenner profiling and Schlumberger sounding using GD-10 Multi-Electrode Resistivity Imaging System and Aquameter CRM 5000, respectively. The present study indicates that there is an occurrence of subsurface inhomogeneous rock materials in the study area. Data collected using GD-10 Multi-Electrode Resistivity Imaging System and Aquameter CRM 5000 supporting each other results, reflecting the equipment's efficiency. This study found that GD-10 Multi-Electrode Resistivity Imaging System is more effective, easy to use, flexible survey layout, and convenient for subsurface heterogeneities assessment.
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