Geographia Technica, Vol 17, Issue 1, 2022, pp. 33-45

FACTORS INFLUENCING SOIL BEHAVIOR AND PROPERTIES OF MASS MOVEMENTS IN THE BLIMBING AREA, BRUNO DISTRICT, PURWOREJO REGENCY, CENTRAL JAVA, INDONESIA

Sari Bahagiarti KUSUMAYUDHA , Riskhy JUMADIL AKHIR, PURWANTO

DOI: 10.21163/GT_2022.171.03

ABSTRACT: The Blimbing area, Bruno district of Purwrejo Regency, Central Java, belongs to a susceptible area for mass movement. Its geomorphology expresses homoclinic hills, undulating plains, and denudated volcanic hills. The lithology is composed of sandstone of the Halang Formation and andesite breccia of the Peniron Formation. A study was conducted that aimed to examine the factors influencing soil behavior and mass movements in this area by applying an analytical descriptive method along with a field survey and surface mapping. There were eight slopes, namely Slope 1 to Slope 8, being examined and analysed. Slope 1 and Slope 5 are composed of high-plastic clay with very expansive properties. Slope 2 is occupied by high-plastic silt with slightly expansive properties. Slope 3, Slope 4, Slope 6, and Slope 7 comprise high-plastic silt with slightly expansive to very expansive properties, while Slope 8 is built of highly fractured rock, with a joint density of 0.36 m. Using the simplified Bishop method, it can be determined that Slope 1 to Slope 7 have safety factor values of 1.095, 1.369, 1.262, 1.128, 1.605, 1.095, and 0.961, respectively. Slope 8 has a rock mass rating (RMR) value of 38, which belongs to class IV (poor rock). It has the potential for wedge and toppling failures. Results of this study indicate that the existence of water in the slopes increases the load on the slopes by 15%, decreasing the cohesion force and reducing the friction angle values, especially when the water content is more than 70%. The type of soil is in the form of high-plastic clay and high-plastic silt that is slightly expansive to very expansive, with low permeability. Thus, water content and the very expansive soil are the main influencing factors for mass movements in the study area.


Keywords: Soil behaviour, Expansive clay, Poor rock, Water content, Mass movement.

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