Analisis Kinematika dan Stabilitas Lereng Pit Barani, PT. Agincourt Resources, Kecamatan Batangtoru, Kabupaten Tapanuli Selatan, Provinsi Sumatra Utara

Dian Astria Permana Padang, Ir. Hendy Setiawan, S.T., M.Eng., Ph.D., IPM. ; Ir. Anastasia Dewi Titisari, M.T., Ph.D., IPU.

2026 | Skripsi | TEKNIK GEOLOGI

Keberadaan kondisi geologi yang kompleks serta variasi kualitas massa batuan di Pit Barani, Tambang Emas Martabe, PT Agincourt Resources, Desa Aek Pining, Kecamatan Batangtoru, Kabupaten Tapanuli Selatan, Sumatera Utara, menjadi faktor kritis yang mengontrol potensi ketidakstabilan lereng penambangan. Penelitian ini bertujuan untuk mengidentifikasi dan menganalisis kondisi geologi sebagai faktor pengontrol kestabilan lereng, menilai kualitas massa batuan menggunakan metode Rock Mass Rating (RMR) dan Geological Strength Index (GSI), mengidentifikasi potensi mekanisme kegagalan lereng melalui analisis kinematika, serta menentukan tingkat kestabilan lereng dengan metode Slope Mass Rating (SMR). Metode yang digunakan meliputi pemetaan geologi, scanline mapping, analisis kualitas massa batuan menggunakan klasifikasi RMR dan GSI, estimasi sudut geser dalam menggunakan pendekatan Hoek-Brown dan Mohr-Coulomb, analisis kinematika, serta analisis kestabilan lereng menggunakan SMR. Hasil penelitian menunjukkan bahwa geomorfologi daerah penelitian terdiri atas satuan lereng tambang (mine wall), lantai tambang (mine floor), jalan tambang (haul road), dan sump. Satuan batuan yang dijumpai meliputi batupasir, konglomerat batupasir, breksi matriks lempung, breksi matriks pasir, dan urat kuarsa. Struktur geologi yang berkembang berupa sesar naik, sesar geser, sesar diperkirakan, kekar ekstensi, dan kekar gerus dengan orientasi arah gaya utama NE–SW yang sejalan dengan tegasan regional. Alterasi yang berkembang terdiri atas alterasi argilik, argilik lanjut, dan silika. Kualitas massa batuan berdasarkan RMR berada pada kategori Fair Rock hingga Good Rock (47 - 79), sedangkan berdasarkan GSI berada pada rentang nilai 42 - 74. Analisis kinematika menunjukkan potensi tipe runtuhan berupa wedge failure, planar failure, oblique toppling, direct toppling, dan flexural toppling, dengan dominasi wedge failure dan oblique toppling. Berdasarkan klasifikasi SMR, kestabilan lereng berada pada kategori tidak stabil hingga stabil, dengan area barat menunjukkan kondisi paling stabil, area timur tidak stabil hingga stabil, dan area selatan tidak stabil hingga stabil sebagian.

The complex geological conditions and variations in rock mass quality at the Barani Pit, Martabe Gold Mine, PT Agincourt Resources, Aek Pining Village, Batangtoru District, South Tapanuli Regency, North Sumatra, are critical factors controlling the potential instability of mining slopes. This study aims to identify and analyze geological conditions as controlling factors of slope stability, assess rock mass quality using the Rock Mass Rating (RMR) and Geological Strength Index (GSI) systems, identify potential slope failure mechanisms through kinematic analysis, and evaluate slope stability using the Slope Mass Rating (SMR) system. The methods employed include geological mapping, scanline mapping, rock mass quality assessment using RMR and GSI classifications, estimation of friction angle using the Hoek-Brown and Mohr-Coulomb approaches, kinematic analysis, and slope stability assessment using SMR. The results show that the geomorphology of the study area consists of mine walls, mine floors, haul roads, and a sump. The rock units identified include sandstone, sandy conglomerate, clay-matrix breccia, sand-matrix breccia, and quartz veins. The geological structures consist of reverse faults, strike-slip faults, inferred faults, extensional joints, and shear joints, with the principal stress direction oriented NE–SW, consistent with the regional stress orientation. The alteration zones consist of argillic, advanced argillic, and silicic alteration. Based on the RMR classification, rock mass quality ranges from Fair Rock to Good Rock, with RMR values of 47–79, while GSI values range from 42–74. Kinematic analysis indicates potential failure mechanisms consisting of wedge failure, planar failure, oblique toppling, direct toppling, and flexural toppling, with wedge failure and oblique toppling being the dominant mechanisms. Based on the SMR classification, slope stability ranges from unstable to stable, with the western area showing the most stable conditions, while the eastern area ranges from unstable to stable and the southern area ranges from unstable to partially stable.

Kata Kunci : Pit Barani, Rock Mass Rating (RMR), Geological Strength Index (GSI), Slope Mass Rating (SMR), kestabilan lereng.