An approach to construct the weathering profile in a hilly granitic terrain based on electrical imaging

For investigation of a granitic hillside at the Kata Noi beach in Phuket, Thailand, a common geotechnical site investigation might not be suitable because it is difficult to bring a drilling rig to make the boreholes on the hillside. As an alternative electrical imaging (EI) survey was proposed. The main issues addressed in this study are how to find the boundary between the weathered and unweathered granites in a gradually changing resistivity pseudo-section and how to assess the effect of hillside topography and the type of electrode array in locating such a boundary. To solve these problems an approach was adopted, including (i) selection of a suitable EI array in the field; (ii) data analysis with topographical correction; and (iii) the incorporation of a conceptual weathering profile in EI data interpretation. As a result, a geological-geoelectrical model was constructed for the weathering profile of granitic rocks at the study site, which can be applied for investigation of similar hilly terrains in Southern Thailand.