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AbstrakSalah satu dampak dari suatu risiko longsoran lereng tambang terbuka adalah jatuhnya material longsor ke dalam tambang yang sedang melakukan operasi tambang yang berakibat dapat menimbulkan terjadinya fatalitas dan/atau cidera bagi pekerja, serta kerusakan properti perusahaan. Oleh sebab itu analisis kestabilan suatu lereng selain digunakan untuk menentukan nilai faktor keamanan (FK) dan probabilitas kelongsoran (PK) lereng, juga dapat memprediksi besaran volume longsoran bila terjadi kegagalan dalam disain lereng. Penelitian ini menggunakan metode kesetimbangan batas (limit equilibrium method) 3 dimensi dalam penentuan volume longsoran lereng dengan lokasi pada tambang terbuka batugamping di Rembang, Jawa Tengah. Ke depan diharapkan pendekatan ini dapat dimanfaatkan para praktisi untuk perencanaan mitigasi kelongsoran lereng. Kata Kunci : Tambang terbuka, stabilitas lereng, metode kesetimbangan batas 3 dimensi, dampak longsoran AbstractOne of the consequences from a risk of open pit failure is the fallen of the failure material in a mine that is doing the mine operation that can cause fatality and/or injury to workers, and damage to company properties. Therefore, the slope stability analysis is not only used to determine the safety factor (SF) and failure probability (FP), but it can also predict the amount of the volume of failure if there is any fault in the slope design. This research used 3D limit equilibrium method in determining the volume of potential failure of an open pit limestone mine in Rembang, Central Java. In the future, it is hoped that this approach can be utilized by practitioners for mitigation of slope failure planning. Keywords : Open pit, slope stability, 3D limit equilibrium method, consequence of failure PENDAHULUANResiko longsoran dapat dikuantifikasi dengan mengalikan probabilitas kelongsoran dan konsekuensi. Manajemen resiko perlu dilakukan untuk meyakinkan potensi

PT X had an accident  of slope failure that caused fatalities and injuries experienced by labor mining, and also some heavy mining equipments  buried  by  materials  that causing companies got financial loss. therefore important to analyze the slope stability of surface mining operation, and predicting total volume of slope failure to anticipate the impact of fatalities/ injuries and financial risks. This research  aim is  to analyze  slope stability before failure conditions, predicting volume of slope failure, and determine position of critical zone using limit equilibrium “Simpilfied Bishop” method 3-dimensional, then doing validation with calculation of actual volume by comparing results of topography maps before and after failure using the cut and fill method. From the result of research, the slope on unstability conditions, actual and predicted volume of  slope failure is  8,629 m3 and 10,559 m3, so percent of calculation error is 18.3% .

ABSTRAK PT. X memiliki disain rencana tambang (pit plan) tahun 2020, yang memerlukan analisis kestabilan lereng guna mengoptimasi cadangan batubara tertambang dan keselamatan operasi penambangan. Pada penelitian ini, analisis kestabilan lereng menggunakan metode elemen hingga (MEH) 3 dimensi. Di samping itu juga dilakukan analisis probabilistik guna memvalidasi hasil perhitungan MEH 3 dimensi. Kompleksitas lapisan batuan yang cukup banyak pada tambang MIP memberikan kesulitan dalam memodelkan dalam analisis 3D menggunakan MEH. Oleh sebab itu digunakan pendekatan pembobotan parameter karakteristik batuan dalam menelaah keakurasian hasil perhitungan faktor keamanan (FK) dan penentuan lokasi lereng kritis. Secara praktis pendekatan pembobotan ini sudah diterapkan di sejumlah tambang batubara di Indonesia, namun terbatas pada analisis 2D. Oleh sebab itu hasil penelitian ini menjadi suatu pencapaian penting yang dapat disosialisasikan dan diaplikasikan oleh para praktisi geoteknik tambang di Indonesia

In detailed exploration, it is necessary to analyze optimal drill hole distance. Drill hole spacing analysis results in optimal drill hole spacing on each coal seam for the coal resources classification. Based on a case study in one of the coal mining companies in North Bengkulu, four coal seams have continuous seams and there is splitting from one seam to four seams. The sediment model generally has a direction of distribution of coal seams trending from northeast to southwest with gentle dip. This research uses geostatistical methods to determine the thickness distribution and variation of coal in the study area and to estimate and classify coal resources and determine the optimal distance from the borehole spacing. Estimation using kriging block results in the value of kriging relative error. Coal resource estimates and variability are determined based on kriging estimation with the relative kriging standard deviation (RKSD) method and the polygon method for classification based on sill distances. The number of drill holes used was 57 drill holes. Based on the calculation of the sill variogram, the coal measured resource is 150 meters, the coal indicated resource is 250 meters and the coal inferred resource is 500 meters. Based on the estimation and classification with relative kriging standard deviation (RKSD), the total coal measured resource is 1.8 million tons, the coal indicated resource is 3.2 million tons and the coal inferred resource is 2.5 million tons with total coal resources.