Electrical Parameters Determination For Shallow Subsurface Using 2-D Resistivity Imaging And Ground Penetrating Radar

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Date
2017-08
Authors
Sulaiman, Nabila
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Publisher
Universiti Sains Malaysia
Abstract
Electrical parameters can be obtained using 2-D resistivity imaging and Ground Penetrating Radar (GPR) methods. 2-D resistivity imaging method measures directly the parameter but calculations are needed for GPR method as the method only provide image of the subsurface. This research aims to determine electrical parameters for shallow subsurface using 2-D resistivity imaging and Ground Penetrating Radar (GPR) methods and to validate electrical parameters related to resistivity, ρ and frequency-dependent conductivity, σ using the two methods. The research also aims to determine the correlation between electrical parameters for horizontal and vertical resolution and establish Frequency-dependent Electrical Parameters worksheet. A borehole was drilled in USM and two boreholes in Sungai Batu for verification. Frequency-dependent conductivity values representing GPR method were calculated using two equations. The first equation is suitable for media that is not influenced by relative dielectric permeability while the second equation is suitable for low-loss dielectric medium. Mean absolute percentage errors (MAPE) for both equations are calculated to determine the efficiency in correlating electrical parameters. USM (weathered granite) has conductivity and resistivity values of 0.41 – 3.03 mS/m and 330 – 2425 Ωm respectively with N-value of 6 – 10. Tupah (weathered granite) display conductivity and resistivity values of 0.09 – 1.38 mS/m and 724 – 10994 Ωm respectively. The conductivity and resistivity values in Bukit Jambul (granitic rock) are 0.13 – 0.25 mS/m and 3999 – 7743 Ωm. Conductivity and resistivity values of Sungai Batu (sedimentation from fluvial system) are 1.2 – 189.18 mS/m and 5 – 878 Ωm with N-value of 7 – 20. Bukit Kalong (weathered limestone) exhibits values of 9.24 – 29.94 mS/m and 33 – 109 Ωm. The electrical parameters for shallow subsurface in all study areas are successfully determined through direct measurement and calculations. The validation of electrical parameters from 2-D resistivity imaging and GPR methods indicate that the values between measured and calculated are in range and correspond well. The correlation of electrical parameters is effective for horizontal and vertical resolution for most of the study areas indicated by low MAPE values. The MAPE for both equations in all study areas are < 5 % except in Sungai Batu. The first equation obtained MAPE > 5 % in Sungai Batu due to high radar energy attenuation value that largely influence the equation. The research is able to establish Frequency-dependent Electrical Parameters worksheet that can be used to calculate electrical parameters for GPR with the aid from 2-D resistivity imaging method.
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Electrical parameters can be obtained using 2-D resistivity imaging , and Ground Penetrating Radar methods.
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