DEVELOPMENT OF THE STABILITY ASSESSMENT OF HYDROTHERMALLY ALTERED VOLCANIC ROCKS SLOPE IN GEDONGSONGO, UNGARAN REGENCY, CENTRAL JAVA, INDONESIA
TUN, KHIN NYEIN NYEIN, Prof. Ir. Dwikorita Karnawati, M.Sc., Ph.D.; Dr. Ahmad Rifa'i, S.T., M.T.; Prof. Hiroyasu Ohtsu
2017 | Disertasi | S3 Teknik Geologi-
Rock slope instabilities are the major hazard for human activities especially in volcanic area where the hydrothermal alteration is dominant and often causing socio - economic losses. The study area, Gedongsongo is a geothermal field area and composed of andesitic lava, perlitic lava and volcanic breccia from the post Ungaran caldera stages and that altered due to hydrothermal alteration. Most of the slope failures are occurred in high intensity of hydrothermal alteration in which andesitic breccia altered to clay by dominant of cohesion. The clay rich soils formed by high intensity of hydrothermal alteration is the most triggering factor for slope failures occurred in the study area. The objective of this reserch is to develop the stability assessment of hydrothermally altered volcanic rocks slope in geothermal area. The research was conducted with series of field work, laboratory analysis, statistical analysis and numerical modeling. Field investigation includes measurements and recordes of slopes and discontinuities, Rock Mass Rating (RMR) parameters, collection of disturbed and undisturbed samples. Laboratory analysis includes petrography, XRD, XRF and engineering properties of hydrothermally altered volcanic rocks. The intensity of hydrothermal alteration was added to the five pre existing parameters of the basic Rock Mass Rating (RMRbasic) by using AHP to develop new rock mass classification (RMRmodify) for stability assessment of hydrothermally altered volcanic rocks slope and Slide 6.0 was used to simulate the slope stability. Rock Mass Rating (RMRmodify) of hydrothermally altered volcanic rocks slope decreased with increased in intensity of alteration. The high intensity of alteration produces thick clay soil formation that creates the failure plane due to the distinctive difference of cohesion between altered zone and unalterd zone which may lead to failures.
Kata Kunci : Hydrothermal alteration, clay rich soils, slope failures, stability assessment, Rock Mass Rating (RMRmodify)
