Correlation of ground penetrating radar and 2-D resistivity imaging methods towards shallow subsurface layer at coastal area

Abstract

There is potential for a long-term subsidence trend on reclaimed land from the shoreline that may cause a geohazard in the future. This study conducted ground penetrating radar (GPR) and the 2-D resistivity method within the residential area in Teluk Kumbar, Pulau Pinang. This residential area is built on reclaimed land about 100 m from the shoreline. The purpose of this study is to identify subsidence in the coastal environment by considering the impact of seasonal variations using both surveys. The influence of wet and dry seasons on GPR and resistivity for the subsurface condition can be determined precisely after evaluating the attenuation of electromagnetic and resistivity values. The resistivity results show three lithology classes: reclaimed soil (>600 Ωm), original soil (<400 Ωm) and hard material (>1000 Ωm) during the dry season. Meanwhile, GPR signals support resistivity results with clear interfaces between reclaimed-original soil and original soil-hard material. GPR signals on layer interfaces have significantly reduced during the wet season due to the increased conductivity. The resistivity results also show decreases as the conductivity increases. Besides, a thick saturated zone of original soil formation has expanded in size during this season with a low resistivity value (<100 Ωm) and weak amplitude reflection. This zone tends to undergo shrink and swell processes due to moisture content changes, which can also correspond to subsidence. Overall, this study provides a good correlation between the performance of geophysical techniques and seasonal changes that accurately characterize the subsurface layer.