JOURNAL OF DEGRADED AND MINING LANDS MANAGEMENT Volume 10, Number 1 (October 2022):3821-3827, doi:10.15243/jdmlm.2022.101.3821 ISSN: 2339-076X (p); 2502-2458 (e), www.jdmlm.ub.ac.id Open Access 3821 Research Article Disposal slope design based on low-plasticity rock’s shear strength in coal mining activities Harjuni Hasan * , Revia Oktaviani, Tommy Trides, Dionisyus Fransiskus Sinaga Department of Mining Engineering, Mulawarman University, Gunung Kelua Campus, St. Sambaliung No. 9 Samarinda 75119, Indonesia * corresponding author : harjunihasan@yahoo.co.id Abstract Article history: Received 5 June 2022 Accepted 19 July 2022 Published 1 October 2022 Slope stability is the primary factor in designing a stable slope. The strength of the disposal slope relies on the characteristic of the dump materials. The rock shear strength denotes the rock's ability to withstand the burden, both constant and dynamic load. The weakest material used as a reference in designing the disposal slope is siltstone in Pulaubalang formation (location-04). The safety value in locations 04 and 02 tend to drop quickly as the inclination increase, while the safety in locations 01 and 03 tend to fall slowly. This indicates that rocks with a lower plasticity index tend to be stronger in steeper slope conditions. The slope geometry was designed to be 10, 15, 20, and 25 m high with a slope angle of 10 o , 15 o , 20 o , 25 o , 30 o , 35 o , 40 o , 45 o , 50 o , 55 o , and 60 o . The slope geometry is considered stable and safe. However, this study suggests that the most effective slope design is the slope with 25 m high, an overall slope of 25.3 o ; a single slope of 35 o ; a berm width of 4.66 m, bench height of 5 m, with a safety factor value of 4.30 (SF= 4.30). Keywords: disposal rock characteristic slope design slope stability To cite this article: Hasan, H., Oktaviani, R., Trides, T. and Sinaga, D.F. 2022. Disposal slope design based on low-plasticity rock’s shear strength in coal mining activities. Journal of Degraded and Mining Lands Management 10(1):3821-3827, doi:10.15243/jdmlm. 2022.101.3821. Introduction Open pit is one of the coal mining systems where all mining activities are performed relatively near the earth's surface. This mining system is profitable only if the coal layer is near the surface. The surface coal mining method typically consists of overburden removal, coal getting, and reclamation (Schissler, 2004). The removal and disposal of overburden may be affected by geological, geotechnical, and environmental factors, so these activities should be carefully planned due to their significant effect on the surface (Oggeri et al., 2019). The embankment slope at the research site consists of claystone and siltstone with low plasticity characteristics. Both materials will expand in wet conditions, shrink in dry conditions, and contain montmorillonite. This type of expansive soil will expand or increase in volume when in contact with air (Davis et al., 2003). Claystone is an aggregate of microscopic and submicroscopic-sized particles derived from the chemical decomposition of constituent rock elements and is plastic. In addition, the permeability of claystone is very low, and if it is dry, it will be hard, and if wet, it will be soft, plastic, and cohesive, expands and shrinks quickly, so it has a significant volume change (Chiarelli et al., 2003). Meanwhile, siltstone consists of coarse-grained minerals with a high rate of pore development (Yu et al., 2021). Overburden dumping is a continuous process during the mining process that requires several considerations in designing and selecting the dumping location (Hustrulid et al., 2000). It is essential as inappropriate overburden dumping, i.e., incompliant to the standard operation, can cause unstable slopes and landslides (Behera et al., 2017). According to Jones et al. (2020), higher soil plasticity, i.e., more comprehensive water content range in the plastic area, tends to be weaker and have a higher shrink-swell, causing an unstable slope. Therefore, performing a simulation based on the physical, mechanic, and