Integration of Ground Penetrating Radar (GPR) and 2-D Resistivity Imaging methods for soil investigation

Rock lithology influences the electrical properties representing soils or rocks. Electrical conductivity value can be measured using geophysical methods like Ground Penetrating Radar (GPR) and 2-D resistivity imaging. The objective of this survey is to integrate GPR, 2-D resistivity imaging and borehole log based on the conductivity value with soil description and N-value from borehole. Borehole is conducted in the middle of the survey line at a distance of 20 m. GPR method used 250 MHz frequency antenna. The result was filtered using Band Pass, Time Varying Gain and DC removal. 2-D resistivity imaging used two arrays; Wenner-Schlumberger and pole-dipole with total distance of 40 m and 1 m minimum electrode spacing using ABEM SAS4000. The results of both arrays are represented in the form of inversion models. Electrical conductivity values for GPR are calculated based on the conductivity values obtained by 2-D resistivity imaging. The conductivity values calculated from GPR are in good agreement with the values from 2-D resistivity imaging method. Electrical conductivity for the top soil is 0.7 - 3.0 mS/m with no soil description and N-value due to imprecise sample of the loose soil condition. The results showed that soil composed of loose silty gravel with some sand at the depth of 1.81 - 2.99 m has higher value of conductivity (0.4 - 3.0 mS/m) while soil dominated by very stiff sandy silt with some rock fragment (gravel) at the depth of 3 -3.5 m has lower conductivity values of 0.4 mS/m to 0.7 mS/m. Soil having low electrical conductivity is probably due to the stiff condition (minimum water content) confirmed by greater N-value. Integration of geophysical methods and geotechnical method is a success and the geophysical parameters can be used in understanding soil condition.