Electronic Theses and Dissertation

Kestabilan lereng merupakan aspek penting dalam pertambangan terbuka, terutama pada area disposal yang dipengaruhi kondisi hidrogeologi seperti tekanan pori air tanah. pt. mifa bersaudara menghadapi masalah kestabilan lereng di in pit dump (ipd) seam c timur, khususnya saat hujan lebat yang meningkatkan tekanan air pori dan menurunkan faktor keamanan (fk). penelitian sebelumnya lebih banyak menyoroti faktor geometri dan sifat mekanik tanah, namun masih terbatas dalam meninjau pengaruh fluktuasi tekanan pori serta efektivitas mitigasi. oleh karena itu, penelitian ini bertujuan menganalisis hubungan antara tekanan pori, muka air tanah (mat), dan fk, menentukan batas aman sesuai kepmen esdm no. 1827 k/30/mem/2018, serta mengevaluasi penerapan dewatering. metode penelitian meliputi uji geser langsung, analisis data piezometer, dan pemodelan numerik menggunakan geostudio (seep/w dan slope/w) pada dua periode: mei 2025 (curah hujan ringan–sedang) dan oktober 2025 (curah hujan tinggi). hasil menunjukkan adanya korelasi positif antara tekanan pori (pwp) dan mat, serta korelasi negatif antara pwp dan fk. pada mei 2025, lereng stabil dengan fk 1,341–1,342, sedangkan oktober 2025 curah hujan ekstrem meningkatkan pwp hingga 737 kpa dan mat 47,7 m, menurunkan fk hingga 1,245 mendekati batas kritis. berdasarkan kepmen esdm no. 1827, batas aman lereng ditetapkan pada fk ≥ 1,3 dengan pwp < 682 kpa dan mat < 42 m. berdasarkan hasil simulasi dewatering penggunaan pompa dapat meningkatkan fk hingga 1,560, membuktikan bahwa pengendalian tekanan pori dengan sistem dewatering terbukti efektif dalam meningkatkan faktor keamanan lereng.

Slope stability is a crucial aspect in open-pit mining, especially in disposal areas influenced by hydrogeological conditions such as groundwater pore pressure. PT. Mifa Bersaudara faces slope stability issues in the In Pit Dump (IPD) of Seam C East, particularly during heavy rainfall, which increases pore water pressure and decreases the factor of safety (FoS). Previous studies have mostly focused on geometry and soil mechanical properties, but have been limited in examining the impact of pore pressure fluctuations and the effectiveness of mitigation measures. Therefore, this study aims to analyze the relationship between pore pressure, groundwater level (GWL), and FoS, determine the safe threshold based on Ministerial Decree of ESDM No. 1827 K/30/MEM/2018, and evaluate the implementation of dewatering. The research methods include direct shear testing, piezometer data analysis, and numerical modeling using GeoStudio (SEEP/W and SLOPE/W) for two periods: May 2025 (light–moderate rainfall) and October 2025 (heavy rainfall). Results show a positive correlation between pore pressure (PWP) and GWL, and a negative correlation between PWP and FoS. In May 2025, the slope was stable with FoS ranging from 1.341 to 1.342, while in October 2025, extreme rainfall increased PWP to 737 kPa and GWL to 47.7 m, reducing the FoS to 1.245—approaching the critical limit. According to the ESDM Ministerial Decree No. 1827, the safety threshold for slopes is set at FoS ≥ 1.3 with PWP < 682 kPa and GWL < 42 m. Based on dewatering simulation results, the use of pumps can increase the FoS up to 1.560, proving that controlling pore pressure through a dewatering system is effective in improving slope safety.