Bench blasting operation on limestone opencast mining at PT. Semen Padang (Persero), Indonesia performed by electric blasting using coloumn loading system. Limestone deposit consist of three type of rock characteritics that are hard limestone, sugary limestone, and jointed limestone. In general, a good blasting design should implementing subdrilling to avoid toe. In this case of study the subdrilling is not need due to the present of many cracks caused by basalt intrusion. Blasting geometry that applied to blast the jointed limestone resulting blasting fragmentation that commonly relatively small in size (<60 cm) but still has some boulders (>60 cm) that caused by coloumn loading system where energy was concentrated in the bottom. Based on field observation of limestone blasting operation and productivity of excavator being used that is Excavator Hitachi EX 1100 with 5.4 m 3 bucket capacity, can be optimized. Especially from the view of drilling and blasting efficiency by modifying blasting geometry and explosive usage to optimize fragmentation to the productivity of excavator being used. Modification that performed is eliminate the sub drilling and change the explosives loading system from coloumn loading to deck loading (include amount of explosives and detonator being used). Based on result of modification, achieve decreasing of boulder percentage as much as 50.25% that is from 9.71% to 4.83% and increasing of excavator productivity up to 36.10% from 1,479 ton/hour to 2,013 ton/hour as well as decreasing blasting cost up to 17.18% from Rp 3,456/ton to Rp 2,862/ton.
ABSTRAKMaterial-material yang terdapat pada waste dump mayoritas merupakan material non-ore (waste rock) dan ditempatkan juga material lumpur dibeberapa area. Lumpur merupakan tanah ekspansif yang memiliki kembang susut air yang ekstrim untuk itu perlu adanya analisis kestabilan lereng berupa nilai Faktor Keamanan (FK) yang diperoleh dari analisis kesetimbangan batas (limit equilibrium) dengan metode Morgenstern-Price dan Probabilitas Kelongsoran (PK) yang dalam perhitungannya menggunakan uji baik suai Kolmogorov-Smirnov. Mengingat Pit berada pada zona subduksi antara Eurasion dan Indo-Australia Plate maka perhitungan dilakukan pada worst case dengan melakukan analisis pendekatan pseudostatik. Tujuan penelitian ini adalah untuk mengetahui nilai FK dan PK dari lereng selanjutnya membandingkan nilai kestabilan lereng dengan hasil program geotech monitoring terhadap adanya penempatan lumpur secara aktual, menghitung nilai FK dan PK pada rencana desain akhir waste dump dan mengkorelasikan ketebalan lumpur terhadap nilai kestabilan yang terjadi. Hasil penelitian menunjukkan bahwa lereng stabil pada kondisi aktual. Tidak terjadi perbedaan perhitungan antara analisis kestabilan lereng aktual dengan peralatan geotech monitoring. Lereng diprediksikan longsor pada simulasi lumpur 3,87 meter pada
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