Compaction Effect on Open-Pit Coal Mine Disposal Material: An Experimental Study, South Kalimantan, Indonesia

Disposal slope stability is a significant matter in open-pit coal mines. Mechanical compaction of disposal materials made of sand-clay mixtures is essential for regulating slope stability and total disposal capacity. This study investigates the effect of mechanical compaction using a 20-ton vibratory compactor on the compaction characteristics and dry density of disposal material. Field investigation was conducted at disposal Block K and Block G of an open-pit coal mine in South Kalimantan, Indonesia, where the materials consist of sandstone-claystone mixtures derived from the Warukin Formation. A large sampling tube (13.3 cm diameter) was used to collect undisturbed samples at depths of up to 1.5 m along multiple disposal lanes that were mechanically compacted. For validation, the measured density values were then compared to California Bearing Ratio estimates derived from Dynamic Cone Penetrometer tests. Field test results with a 2 m lift dumping layer indicate that additional compaction using a 20-ton compactor applied over 40 passes significantly increased dry density value of the disposal material. At a depth of 0.3 m, dry density increased from 1.56 g/cm³ to 1.90 g/cm³ in Block K and from 1.23 g/cm³ to 1.69 g/cm³ in Block G.