Karakterisasi Sifat Geologi Teknik Material Batuan Penyusun Pit Tiwa Abadi Utara, PT Bukit Makmur Mandiri Utama Jobsite IPR, Kutai Kartanegara, Kalimantan Timur

Ignatius Prana Dipa, Ir. I Gde Budi Indrawan, S.T., M.Eng, Ph.D., IPM., Prof. Dr.Eng. Ir. Wahyu Wilopo S.T., M.Eng., IPM., ASEAN.Eng.

2026 | Skripsi | TEKNIK GEOLOGI

Pit Tiwa Abadi Utara merupakan salah satu area penambangan batubara yang dikelola PT Bukit Makmur Mandiri Utama Jobsite IPR yang tersusun oleh material overburden dan interburden dengan litologi batuan sedimen yang beragam sehingga memiliki karakteristik geologi teknik yang berbeda. Penelitian ini bertujuan mengidentifikasi kondisi geologi daerah penelitian, mengkarakterisasi geologi teknik setiap litologi berdasarkan karakteristik batuan utuh (intact rock), sifat fisik, sifat mekanik, tingkat durabilitas, komposisi mineral lempung, dan kondisi massa batuan, serta menganalisis hubungan antarparameter yang memengaruhi karakteristik geologi teknik batuan. Penelitian dilakukan melalui pemetaan geologi, analisis petrografi, analisis X-Ray Diffraction (XRD), pengujian sifat fisik batuan, Point Load Test, Slake Durability Test, dan penilaian Geological Strength Index (GSI) pada empat litologi, yaitu siltstone upper seam T9, sandstone lower seam T9, shaley claystone upper seam T8, dan claystone lower seam T8. Hasil XRD mengidentifikasi mineral lempung berupa smectite, kaolinite, dan illite, dengan komposisi yang bervariasi pada setiap litologi. Hasil penelitian menunjukkan bahwa siltstone upper seam T9 memiliki karakteristik geologi teknik terbaik dengan nilai rata-rata dry density sebesar 2.09 g/cm³, water content 4.04%, UCS 4.86 MPa, SDI 55.34%, serta nilai GSI tertinggi (40-50). Sandstone lower seam T9 menempati urutan kedua dengan karakteristik geologi teknik yang lebih rendah (UCS 0.74 MPa, SDI 29.5%, GSI 30–40), sedangkan shaley claystone upper seam T8 di urutan ketiga (UCS 0.71 MPa, SDI 29.24%, GSI 20–30) dan claystone lower seam T8 dengan karakteristik geologi teknik paling rendah (UCS 0.63 MPa, SDI 24.49%, GSI 15–25). Hasil analisis menunjukkan bahwa karakteristik geologi teknik tidak dikendalikan oleh satu parameter tunggal, tetapi oleh interaksi antara jenis kemas batuan dan faktor pengontrol yang spesifik terhadap masing-masing jenis kemas. Pada litologi grain-supported, karakteristik geologi teknik dikontrol oleh derajat sementasi dan kualitas ikatan kerangka butiran, sedangkan pada litologi matrix-supported dikontrol oleh proporsi mineral lempung dalam matriks. Pada shaley claystone upper seam T8, keberadaan struktur menyerpih yang sejajar dengan laminasi turut menjadi bidang lemah tambahan. Dengan demikian, jenis kemas batuan menjadi faktor yang mendasari perbedaan mekanisme pengontrol karakteristik geologi teknik pada setiap litologi.

Pit Tiwa Abadi Utara is one of the coal mining areas managed by PT Bukit Makmur Mandiri Utama Jobsite IPR, composed of overburden and interburden material with diverse sedimentary rock lithologies, resulting in varying geotechnical characteristics. This study aims to identify the geological conditions of the study area, characterize the geotechnical properties of each lithology based on intact rock characteristics, physical properties, mechanical properties, durability, clay mineral composition, and rock mass condition, as well as to analyze the interrelationships among parameters that influence the geotechnical characteristics of the rocks. The research was conducted through geological mapping, petrographic analysis, X-Ray Diffraction (XRD) analysis, rock physical property testing, Point Load Test, Slake Durability Test, and Geological Strength Index (GSI) assessment on four lithologies, namely siltstone of the upper T9 seam, sandstone of the lower T9 seam (lithic arenite), claystone of the upper T8 seam, and claystone of the lower T8 seam. XRD results identified clay minerals in the form of smectite, kaolinite, and illite, with compositions varying across each lithology. The results showed that the siltstone of the upper T9 seam exhibited the best engineering geology characteristics, with an average dry density of 2.09 g/cm³, water content of 4.04%, UCS of 4.86 MPa, SDI of 55.34%, and the highest GSI value (40–50). The sandstone of the lower T9 seam ranked second, with lower engineering geology characteristics (UCS 0.74 MPa, SDI 29.5%, GSI 30–40), followed by the shaley claystone of the upper T8 seam in third place (UCS 0.71 MPa, SDI 29.24%, GSI 20–30), while the claystone of the lower T8 seam exhibited the lowest engineering geology characteristics among all lithologies (UCS 0.63 MPa, SDI 24.49%, GSI 15–25). The results indicate that the engineering geological characteristics of the studied rocks are governed not by a single parameter, but by the interaction between rock fabric and the controlling factors associated with each fabric type. In grain-supported lithologies, the engineering geological characteristics are primarily influenced by the degree of cementation and the quality of grain-to-grain bonding. In contrast, for matrix-supported lithologies, the proportion of clay minerals within the matrix constitutes the principal controlling factor. In the shaley claystone of the upper T8 seam, the alignment of clay minerals parallel to the lamination additionally forms a potential plane of weakness. These findings demonstrate that rock fabric provides the fundamental framework governing the mechanisms that control the engineering geological characteristics of the studied lithologies.

 

Kata Kunci : Kata kunci: karakteristik geologi teknik, intact rock, mineral lempung, Slake Durability Index, UCS, Geological Strength Index, jenis kemas batuan