Case study of establishing a safe blasting criterion for the pit slopes of an open-pit coal mine

摘要

The average depth of the pits of Pasir Coal Mine, which is located in the island of Kalimantan, Indonesia, has increased during the 17 years after the first development of the mine, and now reaches about 150 m below the ground surface. The pits are mostly composed of three rock layers of mudstone, sandstone, and coal seam. The layers of mudstone and sandstone become the host rocks of the coal seams, but they are in an unconsolidated state and thus so weak in nature. The weakness of these host rocks is believed to provide the primary source of the failure or instability of many slopes in the mine.