Edward Ngii
Anafi Minmahddun
Fathu Nur Rahmah Kudus
Abstract
This study evaluates the stability of a widened road embankment slope by considering the effect of rain infiltration, which is often ignored in practical design. Rainfall infiltrates the soil and alters pore water pressure, reducing its shear strength and potentially causing slope failure. The Phi Index method is used to determine rain infiltration values, using rainfall data from four nearby rain stations over 10 years. The changes in pore water pressure resulting from rain infiltration are incorporated into the slope stability analysis by the limit equilibrium concept using the Spencer method. Back analysis is used to determine the soil shear strength parameters since the CPT test results provide a correlation with values within a certain range. Soil parameters resulting in a safety factor value close to 1.25 (critical condition) were considered representative field conditions. The analysis shows a decrease in the safety factor from 1.50 to 1.31 (12%). These findings emphasize the importance of accounting for rain infiltration in road embankment stability analyses, particularly in areas with high rainfall where the safety factor may fall below the minimum required by Indonesian geotechnical code. When an infiltration effect analysis is not conducted, the safety factor should be increased at least 12% from normal conditions.
Keywords
Infiltration; Pore water pressure; Slope stability; Limit equilibrium; Safety factor.
