Comparative Analysis of Geotextile-Reinforced Embankment Slope Stability Using the Bishop Method in GeoStudio SLOPE/W and Finite Element Analysis in PLAXIS 2D: A Case Study of the Klaten–Purwomartani Toll Road Project, Section 1, Package 1.2, STA 38+000

Abstract

This study aims to analyze the stability of embankment slopes in the Klaten–Purwomartani Toll Road Construction Project Section 1Package 1.2 STA 38+000 by comparing the analysis results using GeoStudio SLOPE/W and PLAXIS 2D, as well as evaluating the effectiveness of geotextile reinforcement and verification using the Bishop method. The research data were obtained from independent laboratory testing of subgrade soil at depths of 1–3 m. The classification results indicate that the subgrade soil is dominated by clay and silt with different shear strength characteristics at each depth, while the embankment material is classified as loamy sand. The analysis without reinforcement shows that increasing embankment height and variations in loading conditions reduce the Safety Factor (SF) value, with the most critical condition occurring at an 8 m embankment height, which does not meet the requirements of SNI 8460:2017 (SF ≥ 1.5). The application of Woven Staple Fiber Polypropylene UNW-60P geotextile reinforcement effectively increases the SF value by approximately 80%, allowing all critical conditions to meet the stability requirements. Verification using the Bishop method produces SF values ranging from 1.626–2.884, all of which satisfy the requirements of SNI 8460:2017. The comparative analysis results show that PLAXIS 2D produces more conservative SF values because it considers stress distribution, deformation, and pore water pressure using the Finite Element Method (FEM) with the Strength Reduction Method (SRM), while GeoStudio SLOPE/W based on the Limit Equilibrium Method (LEM) produces relatively higher SF values and is suitable for preliminary slope stability  evaluation.