Analisis Stabilitas Lereng Dan Perencanaan Dinding Penahan Tanah Pada Sungai Garang, Kampoeng Harmoni, Kecamatan Ungaran Barat, Kabupaten Semarang

Abstract

The slope along the Garang River at the Kampoeng Harmoni housing complex in West Ungaran District, Semarang Regency, has repeatedly experienced landslides caused by river flow scouring the slope toe and removing its lateral support. This study aims to identify soil characteristics, analyze slope stability, and assess the scour depth at the slope toe to inform the design of a retaining wall. Stability analysis was performed manually using the Fellenius and Bishop methods and verified with Plaxis 2D, while scour was analyzed using the regime method (Lacey). Soil data were obtained from laboratory tests on samples from three boreholes (BH1–BH3) reaching a depth of 20 m. The results indicate that the site soils, classified under the USCS, consist of SM (silty sand), SW (well-graded sand), and MH (high-plasticity silt). The existing slope safety factors were 1.15–1.24 (Fellenius and Bishop; "somewhat stable" category) and 1.29–1.30 (Plaxis; "moderate" category), with a toe scour depth of 0.610 m identified as a contributing factor to the landslides. Based on these conditions, a gravity retaining wall with a height of 7.8 m and a base width of 7.0 m was designed; this design increases the safety factor to 1.67 (static) and 1.68 (consolidation), making it an effective and safe solution for mitigating landslide risk.