Pengaruh Keberadaan Material Butir Pasir terhadap Sifat Mekanik Timbunan pada Studi Kasus Disposal Pit SJS PT Bukit Asam (Persero) Tbk Unit Pertambangan Tanjung Enim

Abstract

Embankment slope stability is a critical challenge in open-pit coal mining operations, particularly within the Tanjung Enim Mining Unit (UPTE) of PT Bukit Asam Tbk. This study investigates the influence of varying clay and sand compositions on the physical and mechanical properties of embankment geomaterials to determine the optimal configuration for operational stability. An experimental research design was conducted using material samples from Pit SJS, involving five composition variations: 100% clay; 75% clay – 25% sand; 50% clay – 50% sand; 25% clay – 75% sand; and 100% sand. Geotechnical parameters were evaluated through Standard Proctor compaction tests and Direct Shear tests to determine maximum dry density, optimum moisture content, bearing capacity, cohesion, and internal friction angle. The results demonstrate that both maximum dry density and bearing capacity exhibit an increasing trend as sand content rises, reaching peak values at the 50% clay – 50% sand composition before declining at higher sand ratios. Conversely, optimum moisture content significantly decreases as sand content increases. Shear strength analysis reveals that cohesion reaches its maximum at the 50/50 ratio, while pure sand (100% sand) exhibits significant "apparent cohesion" due to the interlocking effect of sand grains, which enhances shear resistance despite the material's non-cohesive theoretical nature. Slope stability simulations indicate that the 50% clay – 50% sand mixture provides the most superior mechanical performance for structured benching, ensuring a Safety Factor (SF) 1.35. This study concludes that an equal balance of clay and sand optimizes stability by combining cohesive bonding with high bearing capacity and grain interlocking.