Simulation of Kalirejo Road Side Slope based on Altered Andesite Characters, Kulon Progo Regency, Indonesia

ABSTRACT. This study is performed to investigate the characteristics of intrusive andesite rock consisting Kalirejo Road Side Slope located in Kulon Progo Mountains. The rocks slope are identified by visual observation hand specimens field, petrographic and X-ray Diffraction (XRD) analyses samples laboratory, upon which genetic classification determined. altered types determined presence specific minerals XRD analyses. alteration intensity examined comparing amount secondary primary observed developments weathering field GSI based on laboratory-based Chemical Index Alteration (CIA) engineering properties rocks. results show that typically consisted 33.2 59.2% plagioclase, 1.4 5.1% quartz, therefore, classified as andesite. halloysite, montmorillonite, kaolinite indicated parent have undergone argillic alteration. Meanwhile, percentages indicate moderate high intensity. Based characteristics, research area fresh, slight weathered complete residual soil. CIA values increased with increase weathering. Identification appeared be good agreement those analysis results. uniaxial compressive strength (UCS) soils point load tests. Engineering using ASTM standard procedures. In lower part roadside, consists fresh slightly rocks, relatively medium strong upper profile contained completely soil, had very low strength, weak soil.Keywords: andesite, alteration, Geological Strength (GSI), hydrothermal roadside slope,