PROFIL BIDANG GELINCIR, KARAKTERISTIK TANAH, DAN KESTABILAN LERENG DI ZONA SESAR LEMBANG , GUNUNG BATU, JAWA BARAT - Cahyanisa Alifa Pramesti, - (2023)
Telah dilakukan pengambilan data seismik refraksi dan sampel tanah di Gunung Batu, Lembang, Jawa Barat. Salah satu zona Sesar Lembang yakni patahan sesar geser aktif. Akibat dari pergerakan sesar aktif, salah satunya bencana longsor. Pengambilan data dilakukan pada dua lintasan arah utara - selatan, panjang lintasan 1 (GBT01) ±94 meter, lintasan 2 (GBT02) ± 70 meter, menggunakan alat McSeis - SX48 , 48 Geophone, jarak spasi 2 meter, untuk menunjukan profil bawah permukaan. mengetahui area bidang gelincir, melakukan pengolahan sampel tanah pada Laboratorium BRIN. Untuk mengetahui sifat fisik dan keteknikan tanah dalam analisis karakteristik tanah. Data-data digunakan analisis pemodelan kestabilan lereng, menggunakan pendekatan kesetimbangan batas umum (GLE), menentukan kestabilan lereng pada kondisi kritis. Pendekatan pusat massa, gesekan coulomb sederhana, untuk prediksi kecepatan dan jarak jangkauan longsor pada lokasi ini. Berdasarkan profil bawah permukaan metode seismik refraksi didapatkan tiga lapisan, berupa Lanau, Pelapukan Andesit, Andesit, dengan prediksi bidang gelincir pada lapisan pertama dengan jenis lanau Anorganik, GBT01 panjang sebesar 35-36 meter, kedalaman ±3-4 meter. GBT02 panjang 21-22 meter, kedalaman ±3-3.5 meter. Hasil analisis geoteknik GBT01&GBT02 dijadikan parameter permodelan kestabilan lereng kritis (FK~1), yakni Berat isi 12.77 kN/m^3&11.68 kN/m^3, Kohesi 9.50 kPa&3.94 kPa,Sudut Geser 21.85°& 35.94°. Hasil Software Geostudio dan pyBIMstab GBT01-GBT02, prediksi kecepatan sebesar 3.86 m/s & 3.73 m/s kategori extreme dan 2.94 m/s & 2.97 m/s kategori cepat. GBT01-GBT02 masing-masing sebesar 12.56 meter &12.09 meter dan 23.83 meter & 23.37 meter. Pergerakan lereng termasuk pada kategori tipe pergerakan translasi, dengan arah longsoran menuju ke utara. Seismik refraction data and soil samples have been collected at Gunung Batu, Lembang, West Java. One of the fault zones in Lembang is an active strike-slip fault. One of the consequences of active fault movement is landslide disasters. The data collection was carried out along two north-south tracks: Track 1 (GBT01) with a length of approximately 94 meters and Track 2 (GBT02) with a length of approximately 70 meters. The McSeis - SX48 instrument was used, equipped with 48 geophones spaced at 2-meter intervals, to provide subsurface profiles. In order to determine the sliding area, soil samples were processed at the BRIN Laboratory. The physical and engineering properties of the soil were analyzed to study the soil characteristics. The data obtained were used for slope stability modeling analysis using the General Limit Equilibrium (GLE) approach to determine slope stability under critical conditions. The center of mass approach and simple Coulomb friction were employed to predict the velocity and range of the landslide at the location. Based on the subsurface profile obtained from the seismik refraction method, three layers were identified: silt, Weathered Andesite, and Andesite. The predicted sliding plane was found in the first layer, consisting of Inorganic Silt, with a length of 35-36 meters for GBT01 and a depth of approximately 3-4 meters. For GBT02, the length was 21-22 meters, with a depth of approximately 3-3.5 meters. The geotechnical analysis results of GBT01 and GBT02 were used as parameters for critical slope stability modeling (FK~1), with unit weights of 12.77 kN/m^3 and 11.68 kN/m^3, cohesion values of 9.50 kPa and 3.94 kPa, and friction angles of 21.85° and 35.94°, respectively. The Geostudio and pyBIMstab software produced the following predictions for GBT01-GBT02: extreme velocity of 3.86 m/s and 3.73 m/s, and fast velocity of 2.94 m/s and 2.97 m/s. The corresponding distances traveled were 12.56 meters and 12.09 meters for GBT01, and 23.83 meters and 23.37 meters for GBT02. The slope movement falls under the category of translational movement, with the landslides moving towards the north.