ANGLE OF SLOPE AND SLOPE SAFETY FACTOR RELATIONSHIP IN GENDOL RIVER, SOUTHERN SLOPE OF MERAPI VOLCANO, YOGYAKARTA

Abstract

The southern slopes of Merapi Volcano in Yogyakarta are mostly the dangerous zone of Merapi. The slope geometry resulted from the Merapi Volcanic eruption forms an area with the potential of mass movement and disturbance of slope stability. On this basis, this study aims to design a control model for slope geometry in the Volcanic Mount of Merapi materials. It used direct lithology observation and geometry measurements in the field, supported by an analysis of the physical and mechanical properties of soil samples. Slope safety analysis was carried out on 35 slope locations, 6 of which were located on the cliffs of the Gendol River. This analysis used Slope W software, and the relationship of slope safety factors that can be formed by certain slope angles follows the equation of y = 21.4x^-0.744 with a very strong correlation (r = 0.92), where "y" is a slope safety factor, while "x" is the angle of the slope. Based on the research results, it is can be deduced that the relationship between slope safety factors that can be formed by certain slope angles, in lahar deposits is that if the slope angle is increasing then the value of slope stability factor will be reduced. The stable classes are FS>1.25 with slope angles of <43º, the critical class is 1.07> FS>1.25 with slope angles 44º - 54º and labile class is FS <1.07 with slope angles of >55º.