Electronic Theses and Dissertation

Pemetaan geologi dilakukan di Kecamatan Birem Bayeun, Kabupaten Aceh Timur, Provinsi Aceh untuk mengidentifikasi kondisi geologi dan potensi bahaya longsor. Daerah penelitian tersusun atas Formasi Keutapang, Formasi Seureula, dan Formasi Julu Rayeu yang berumur Miosen Akhir hingga Pliosen. Wilayah ini termasuk daerah dengan tingkat bahaya longsor sedang hingga tinggi akibat dominasi batuan sedimen yang relatif lunak, mudah lapuk, dan rentan mengalami kejenuhan air saat curah hujan meningkat. Keberadaan permukiman di sekitar lereng turut meningkatkan risiko terhadap masyarakat dan infrastruktur sehingga diperlukan pembaruan data geologi yang lebih detail dan aktual. Penelitian ini bertujuan untuk memetakan kondisi geologi dan geomorfologi dengan luas 25 km² serta menganalisis kestabilan lereng menggunakan pendekatan geoteknik. Metode yang digunakan pemetaan geologi dan geomorfologi secara langsung di lapangan, serta pengolahan data menggunakan ArcGIS untuk menghasilkan peta lintasan, peta geologi, peta geomorfologi, dan peta pola aliran. Analisis kestabilan lereng difokuskan pada satu lereng representatif dengan pengambilan sampel tanah yang diuji di laboratorium untuk memperoleh parameter sifat fisik dan mekanik tanah. Analisis dilakukan menggunakan Metode Bishop Disederhanakan dengan software Rocscience Slide 6.0 untuk memperoleh nilai faktor keamanan secara numerik. Kemudian dibandingkan dengan perhitungan manual melalui pemodelan tiga variasi bidang gelincir pada lereng yang sama menggunakan AutoCAD. Hasil penelitian menunjukkan bahwa geomorfologi daerah penelitian didominasi oleh satuan denudasional yaitu satuan D1 dan satuan D5. Satuan batuan daerah penelitian terdiri atas satuan Batupasir Formasi Keutapang, Satuan Perselingan Batupasir dan Batulempung Formasi Seureula, serta satuan Batupasir Formasi Julu Rayeu, dengan litologi berupa batupasir, batulempung, perselingan batupasir–batulempung, serta sisipan lignit dan konglomerat. Nilai faktor keamanan lereng yang dihasilkan secara numerik sebesar 1,499 sedangkan perhitungan manual sebesar 1,49;1,45;1,51 dengan nilai representatif 1,49 yang menunjukkan kondisi relatif stabil namun memiliki kerentanan sedang terhadap longsor. Oleh karena itu, upaya mitigasi seperti perkuatan lereng dan pengelolaan drainase untuk mengurangi risiko longsor di wilayah penelitian perlu dilakukan.
Kata kunci: Pemetaan Geologi, Geoteknik, Kestabilan lereng, Metode Bishop Disederhanakan, dan Faktor keamanan

Geological mapping was conducted in Birem Bayeun District, East Aceh Regency, Aceh Province, to identify the geological conditions and assess landslide hazards in the study area. The area is composed of the Keutapang Formation, Seureula Formation, and Julu Rayeu Formation, which range in age from the Late Miocene to the Pliocene. The study area is classified as having moderate to high landslide susceptibility due to the predominance of relatively weak sedimentary rocks that are easily weathered and prone to water saturation during periods of intense rainfall. The presence of settlements on and around the slopes further increases the potential risk to local communities and infrastructure, highlighting the need for updated and detailed geological information. This study aims to map the geological and geomorphological conditions of a 25 km² area and to analyze slope stability using a geotechnical approach. The methods employed include direct geological and geomorphological field mapping, followed by spatial data processing using ArcGIS to produce traverse maps, geological maps, geomorphological maps, and drainage pattern maps. Slope stability analysis was focused on a representative slope where soil samples were collected and tested in the laboratory to determine their physical and mechanical properties. The stability analysis was carried out using the Simplified Bishop Method through Rocscience Slide 6.0 software to obtain numerical safety factor values. These results were then compared with manual calculations based on three different slip surface models developed in AutoCAD. The results indicate that the study area is dominated by denudational geomorphological units, namely Unit D1 and Unit D5. The geological units consist of the Keutapang Sandstone Unit, the Interbedded Sandstone and Claystone Unit of the Seureula Formation, and the Julu Rayeu Sandstone Unit. The identified lithologies include sandstone, claystone, interbedded sandstone–claystone, as well as lignite and conglomerate intercalations. The numerical analysis yielded a factor of safety of 1.499, while the manual calculations produced values of 1.49, 1.45, and 1.51, with a representative value of 1.49. These results indicate that the slope is relatively stable but exhibits moderate susceptibility to landslides. Therefore, mitigation measures such as slope reinforcement and proper drainage management are recommended to reduce landslide risk within the study area. Keywords: Geological Mapping, Geotechnics, Slope Stability, Simplified Bishop Method, and Factor of Safety.