Electronic Theses and Dissertation

ABSTRAK
Pemetaan geologi dilakukan untuk mengetahui kondisi geologi daerah penelitian
yang meliputi litologi, geomorfologi, struktur geologi, dan kestabilan lereng.
Daerah penelitian berada di Kecamatan Langsa Baro dan sekitarnya, Kota Langsa,
Provinsi Aceh dengan luas ±25 km². Secara geografis berada pada 4º 28’ 59,78” -
4º 26’ 17” LU dan 97º 51’ 38.86” - 97º 54’ 21.05” BT. Wilayah ini tersusun oleh
satuan batuan sedimen dari Formasi Keutapang, Formasi Seureula, dan Formasi
Julu Rayeu (Cameron dkk., 1981) dengan karakteristik litologi yang berbeda. Jenis
batuan yang dijumpai di daerah penelitian terdiri atas batupasir, perselingan
batupasir dan batulempung, perselingan batupasir dan konglomerat, batulempung,
serta sisipan lempung lignit. Berdasarkan klasifikasi Van Zuidam 1983, daerah
penelitian dibagi menjadi dua satuan geomorfologi, yaitu satuan perbukitan dan
lereng denudasional dengan erosi kecil (D1) serta satuan dataran denudasional
(D5). Hasil pengujian tanah berdasarkan sistem klasifikasi USCS menunjukkan
bahwa sampel tanah termasuk kelompok SC dan ML, sedangkan berdasarkan
sistem klasifikasi AASHTO termasuk kelompok A-6 dan A-7-6. Berdasarkan
analisis kestabilan lereng, pada kondisi tidak jenuh diperoleh nilai faktor keamanan
sebesar FK = 1,3520 menggunakan Metode Bishop Disederhanakan dan FK =
1,5135 menggunakan Software Plaxis 8.6 yang menunjukkan kondisi lereng aman.
Sementara itu, pada kondisi jenuh diperoleh nilai faktor keamanan sebesar FK =
0,7609 menggunakan Metode Bishop Disederhanakan dan FK = 0,8982
menggunakan Software Plaxis 8.6. yang menunjukkan kondisi lereng berpotensi
tidak aman dan berpotensi mengalami longsor akibat peningkatan kadar air. Hasil
analisis menunjukkan bahwa peningkatan kadar air sangat memengaruhi kestabilan
lereng. Oleh karena itu, diperlukan penanganan teknis berupa sistem drainase
lereng sebagai langkah mitigasi untuk mengurangi potensi longsor.
Kata Kunci: Pemetaan Geologi, Kestabilan Lereng, Faktor Keamanan, Drainase
Lereng.

ABSTRACT Geological mapping was conducted to determine the geological conditions of the study area, including lithology, geomorphology, geological structures, and slope stability. The study area is located in Langsa Baro Subdistrict and its surroundings, Langsa City, Aceh Province, covering an area of approximately 25 km². Geographically, it is situated at 4° 28' 59.78" - 4° 26' 17" N and 97° 51' 38.86"- 97° 54' 21.05" E. This region consists of sedimentary rock units from the Keutapang Formation, Seureula Formation, and Julu Rayeu Formation (Cameron et al., 1981), each with distinct lithological characteristics. The rock types found in the study area consist of sandstone, interbeds of sandstone and shale, interbeds of sandstone and conglomerate, shale, and lignite-bearing clay interbeds. Based on Van Zuidam's 1983 classification, the study area is divided into two geomorphological units: a unit of hills and denudational slopes with minor erosion (D1) and a unit of denudational plains (D5). Soil test results based on the USCS classification system indicate that the soil samples belong to the SC and ML groups, while based on the AASHTO classification system, they belong to groups A-6 and A-7-6. Based on slope stability analysis, under unsaturated conditions, a safety factor of FK = 1.3520 was obtained using the Simplified Bishop Method and FK 1.5135 using Plaxis 8.6 software, indicating that the slope is stable. Meanwhile, under saturated conditions, a safety factor of FK = 0.7609 was obtained using the Simplified Bishop Method and FK = 0.8982 using Plaxis 8.6 software, indicating that the slope is potentially unstable and at risk of landslides due to increased moisture content. The analysis results show that an increase in moisture content significantly affects slope stability. Therefore, technical measures in the form of a slope drainage system are required as a mitigation step to reduce the potential for landslides. Keywords: Geological Mapping, Slope Stability, Safety Factor, Slope Drainage