Identification of cave stability using integrated electromagnetic VLF, resistivity and rock mechanical method, case study: Pindul Cave Tourism, Gunung Kidul, Yogyakarta

Abstract

The geotourism area of Pindul Cave requires a good planning review in mitigation efforts. Studies on the stability and strength of the cave walls determine the cave mitigation plan. The research method used is the integration of electromagnetic Very Low Frequency (VLF), resistivity and rock mechanical. Based on the analysis of integration method, obtained 17 m of maximum penetration from resistivity cross section while electromagnetic section equal to 80 meter. The existence of underground river flow in this method is indicated by the range of electric current density (RAE) 65-100% (yellow-red) with a depth of ground level from 10 m to immeasurable by the tool. Around of the cave cavity there are other cavities that are invisible. Allegedly, this cavity is also another branching of the Pindul cave underground river system. Based on the analysis of rock mechanical by using the Rock Mass Rating (RMR) classification indicates that generally rocks include class II (good). Analysis of rock mechanics shows that the geological structure factor is more dominant in cave stability, with a percentage of 65%. The data integration is used as the basis for 3D cave geometry modeling, quantitative and qualitative cave stability assesment as well as recommendations of safe zones and mitigation recommendations.