Kestabilan Lereng Optimal Tambang Batubara Highwall dan Lowwall disertai Probabilitas Kelongsorannya PT. XYZ di Kecamatan Lahei Kabupaten Barito Utara Provinsi Kalimantan Tengah

Abstract

Abstract. Slope stability is an important issue in the planning and operation of open mines. The design of a stable and precise slope geometry will have a large impact on the economy and the continuity of mine operation to maximize production. To find out the design of a stable slope, slope stability analyses are needed to get the number of safety factors from a particular slope shape. This company will open a new pit, so slope stability analyses along with probability of landslides resulting in optimal slope design is required. The study was conducted with the aim to identify the sequence of stratigraphic positions and physical-mechanical properties of rocks at the study site by rotary drilling, and to determine the stability of slope geometry of pits being based on design recommendations  of highwall and lowwall overall pit slopes of optimal safety factors and lowest values of failure probabilities. In analyzing the stability of slopes required data from laboratory testing results, including data on physical and mechanical properties of rocks. These data are then tested for normality in order to match the variables using the Kolmogorov-Smirnov method using SPSS 26.0 Statistics Software. Slope stability analysis is performed using the Bishop boundary equilibrium method accompanied by probabilistic analysis using the Monte Carlo and Latin-Hypercube method using Slide 6.0 Software. Based on the results of the study, it can be seen that the constituent rocks at the study site consist of sandstone, claystone, siltstone and coal. Classification of rock strength is classified as very soft. Single safe slope geometries are H = 15 m and θ = 62⁰ for sandstone, H = 10 m and θ = 60⁰ for claystone, H = 8 m and θ = 60⁰ for siltstone and H = 12 m and θ = 60⁰ for coal. While the slope design recommendations for highwall A are H = 95.79 m and θ = 48⁰, highwall B is H = 90.61 m and θ = 35⁰, highwall C is H = 95.00 m and θ = 28⁰ and highwall D is H = 78.30 m and θ = 48⁰ and for lowwall A is H = 105.64 m and θ = 24⁰, lowwall B is H = 94.00 m and θ = 22⁰, lowwall C is H = 113.66 m and θ = 18⁰ and lowwall D is H = 77.00 m and θ = 40⁰.

Keywords: Slope Stability, Highwall, Lowwall, Factor of Safety, Failure Probability

Abstrak. Kestabilan lereng merupakan faktor penting dalam perencanaan dan operasional tambang terbuka. Desain dari lereng yang stabil dan tepat akan mempunyai dampak yang besar terhadap keekonomian serta kontinuitas produksi tambang. Untuk mengetahui desain lereng yang stabil tersebut maka diperlukan analisis kestabilan lereng. Perusahaan tempat penelitian akan membuka pit baru sehingga diperlukan analisis kestabilan lereng disertai probabilitas kelongsoran  untuk memperolah desain lereng yang optimal. Penelitian dilakukan dengan tujuan untuk mengetahui stratigrafi dan karakteristik batuan pada lokasi penelitian, mengetahui geometri lereng optimal pada lokasi penelitian serta menentukan rekomendasi desain pada lereng untuk highwall dan lowwall dengan nilai FK dan PK yang optimal. Dalam melakukan analisis kestabilan lereng diperlukan data hasil pengujian laboratorium, meliputi data sifat fisik dan sifat mekanik batuan. Data-data tersebut kemudian diuji normalitas dengan tujuan untuk mencocokan variabel menggunakan metode Kolmogorov - Smirnov menggunakan Software Statistika  SPSS  26.0.  Analisis  kestabilan  lereng  dilakukan  dengan  menggunakan  metode kesetimbangan batas Bishop disertai analisis probabilistik dengan menggunakan metode Monte Carlo dan Latin – Hypercube menggunakan Software Slide 6.0. Berdasarkan hasil penelitian, dapat diketahui bahwa batuan penyusun pada lokasi penelitian terdiri dari sandstone, claystone, siltstone dan coal. Klasifikasi kekuatan batuan tergolong sangat lunak. Geometri lereng tunggal yang aman yaitu  H = 15 m dan θ = 62⁰ untuk sandstone, H = 10 m dan θ = 60⁰ untuk claystone, H = 8 m dan θ = 60⁰ untuk siltstone dan H = 12 m dan θ = 60⁰ untuk coal. Sedangkan rekomendasi desain lereng untuk highwall A yaitu H = 95,79 m dan θ = 48⁰, highwall B yaitu H = 90,61 m dan θ = 35⁰, highwall C yaitu H = 95,00 m dan θ = 28⁰ dan highwall D yaitu H = 78,30 m dan θ = 48⁰  dan untuk lowwall A yaitu H = 105,64 m dan θ = 24⁰, lowwall B yaitu H = 94,00 m dan θ = 22⁰, lowwall C yaitu H = 113,66 m dan θ = 18⁰ dan lowwall D yaitu H = 77,00 m dan θ = 40⁰.

Kata Kunci: Kestabilan Lereng, Highwall, Lowwall, Faktor Keamanan (FK), Probabilitas Kelongsoran (PK)