MECHANISM AND CHARACTERISTICS OF THE LANDSLIDES IN BONE BOLANGO REGENCY, GORONTALO PROVINCE, INDONESIA

Abstract

One of the regencies in Gorontalo Province, Indonesia, Bone Bolango is an area in which landslides occur frequently. This study was at identifying the mechanism and characteristics of landslides in Bone Bolango Regency. This study is important to minimize hazards caused by this disaster. Data were obtained from the results of site survey, surface geological survey and geotechnical investigation. Cohesion during the dry season ranged between 0-15kPa, and the angle of internal friction ranged between 30o-44o. The topography of this area indicates a steep slope (>40°), with weathered rock and discontinuity. These internal factors made the slopes prone to landslide. Meanwhile, external factors that trigger landslides are high precipitation (>100mm), the absence of vegetation covering the slopes, as well as land use on the slopes. In general, the types of the landslide in the study area were debris flows, rotational slides, and rock falls. At the period of high precipitation, the rate of infiltration of rainwater into the soil was slower than the rate of the
increase in the volume of rainwater deposited and flowing into the slope surface, resulting in the debris flow. Slope-forming material became soft due to the rise of groundwater levels. This caused a decrease in shear strength and pore water pressure that turned into positive. In the rock slope, rainwater filled the crack of slope discontinuity area so that rock got loose and fell freely. Therefore, a further research is necessary to conduct in order to determine the most accurate and efficient method for slope stability.