Engineering Geology and Slope Stability of West Pit Coal Mine of PT. Tawabu Mineral Resource, East Kalimantan, Indonesia

Rama Tri Saksono; I Gde Budi Indrawan; Wahyu Wilopo

doi:10.22146/jag.76532

Engineering Geology and Slope Stability of West Pit Coal Mine of PT. Tawabu Mineral Resource, East Kalimantan, Indonesia

https://doi.org/10.22146/jag.76532

Rama Tri Saksono⁽¹⁾, I Gde Budi Indrawan^(2*), Wahyu Wilopo⁽³⁾

(1) Department of Geological Engineering, Universitas Gadjah Mada
(2) Department of Geological Engineering, Universitas Gadjah Mada
(3) Department of Geological Engineering, Universitas Gadjah Mada
(*) Corresponding Author

Abstract

The research area was located in the west pit of the open pit coal mine of PT. Tawabu Mineral Resource (TMR) which is located in Bengalon District, East Kutai Regency, East Kalimantan Province, Indonesia. The research was driven by several landslides that occurred in the research area, but the engineering geological conditions and stability of the remaining slopes have not been evaluated. The objectives of this study were to better understand the engineering geological conditions and stability of the research area. The engineering geological conditions (i.e., geomorphology, rock and soil, geological structure, and groundwater conditions) were evaluated by photogrametric analyses, field observations, and analyses of borehole logs and laboratory test results. The slope stability analyses were firstly carried out by conducting back stability analyses of failed slope on the northern lowwall slope segment. The shear strength parameters obtained from the back analyses were then used for forward stability analyses of the remaining 10 lowwall and highwall slopes. The slope stability analyses involved deterministic and probabilistic analyses, under static and dynamic using the limit equilibrium method (LEM). The results showed that the research area and the surrounding consisted of two geomorphological units, namely the alluvial plain and structural hills. Rocks in the study area consisted of claystone, sandstone, and coal with a general layer strike direction of N59°E – N63°E with a dip of 19°-26°. These rocks were grouped into two lithological units, namely the alternating of claystone and sandstone unit and alternating of sandstone and claystone unit. The geological structures were identified on the highwall, from west to east namely major sinistral shear fault with a relative direction of NNE-SSW, two minor sinistral shear faults with a relative direction of NE-SW, and a major dextral shear fault with a relative direction of NW-SE. These geological structures were interpreted as being formed by the folding process. The groundwater level was estimated at a level of -45 m to 20 m. The slope stability analyses showed that only the East HW-4 slope, which was located on the east highwall, was unstable. It is recommended to optimize the slope by either lowering the groundwater elevation by 4 m from the actual level or by reducing the angle the overall slope to 31°.

Keywords

back stability analysis; coal mine; engineering geology; forward stability analysis; slope optimization

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References

Abdulai, M., Sharifzadeh, M. (2019) Uncertainty and Reliability Analysis of Open Pit Rock Slopes: A Critical Review of Methods of Analysis, Geotech Geol Eng (2019), 37: 1223-1247.

Abramson, W.L., Lee, T.S., Sharma, S., Boyce, G.M. (2002) Slope Stability and Stabilization Methods 2nd ed., New York: John Wiley & Sons, Inc., 712.

Bachtiar, A. (2004) Kerangka Stratigrafi Sekuen dan Karakter Batuan Induk Miosen Awal di Cekungain Kutai Hilir, Kalimantan Timur, Doctoral Dissertation, Institut Teknologi Bandung.

Bachtiar, A., Nugroho, D.H.H., Azzaino, Z., Utomo, W., Krisyunianto, A., Sani, M. (2013a) Surface Data Re-evaluation, Eocene Source Rock Potential and Hydrocarbon Seepage, And Eocene Sand Reservoir Prospectivity in West Sangatta Northern Kutai Basin, Proceedings Indonesian Petroleum Association, 37th Annual Convention & Exhibition, 6.

Bachtiar, A., Purnama, Y.S., Suandhi, P.A., Krisyunainto, A., Rozalli, M., Nugroho, D.H.H., Suleiman, A. (2013b) The Tertiary Paleogeography of the Kutai basin And Its Unexplored Hydrocarbon Plays, in Proceedings Indonesian Petroleum Association, 37th Annual Convention & Exhibition.

Bell, F.G. (2007) Engineering Geology, 2nd ed., Elsevier, 581.

Bergbauer, S., Pollard, D. D. (2004) A new conceptual fold-fracture model including prefolding joints, based on the Emigrant Gap anticline, Wyoming: Geological Society of America Bulletin, v. 116, no. 3/4, 294-307.

Cloke, I.R., Moss, S.J., Craig, J. (1999) Structural Controls on the evolution of the Kutai Basin, East Kalimantan, Journal of Asian Earth Sciences, 137-156.

Davis, G. H., Reynolds, S. J., Cluth, C. (2012) Structural geology of rocks and regions, Wiley, Hoboken, 839.

ESDM Ministry (2018) Keputusan Menteri Energi Dan Sumber Daya dan Mineral Nomor 1827 K/30/MEM/2018 Tentang Pedoman Pelaksanaan Kaidah Teknik Pertambangan Yang Baik, 370.

Gonzalez de Vallejo, L.G., Ferrer, M. (2011) Geological Engineering, Boca Raton: CRC Press, 669.

Howard, A.D. (1967) Drainage Analysis in Geologic Interpretation: A Summation, in American Association of Petroleum Geologist Bulletin, 51, 2246-2259.

Ikatan Ahli Geologi Indonesia (IAGI) (1996) Sandi Stratigrafi Indonesia, IAGI, 34.

Lorig, L., Stacey, P., Read, J. (2010) Slope Design Method, in Read, J. Stacey, P. (eds), Guidelines for Open Pit Slope Design, CSIRO Publishing, 237-264.

Morgenstern, N.R., Price, V.E. (1965) The Analysis of the Stability of General Slip Surfaces. Géotechnique, 15, 79-93.

Moss, S.J., Chambers, J.L.C. (1999) Tertiary facies architecture in the Kutai Basin, Kalimantan, Indonesia, in Journal of Asian Earth Sciences 17 (1999). 157-181.

Nuay, E.S., Astarita, A., Edwards., K. (1985) Early Middle Miocene Deltaic Progradation in the Southern Kutai Basin, in 14th Annual IPA Convention Proceedings (Volume I), 63-81.

Saksono, R.T. (2022) Evaluasi Kestabilan Lereng Tambang Batubara di Pit Barat PT. Tawabu Mineral Resource, Kalimantan Timur, Magister Teknik Geologi UGM (Thesis). 474.

Sandria, G.J. (2014) Geologi Dan Perhitungan Sumberdaya Batubara Dengan Metode Cross Section Daerah Sepaso Selatan, Kecamatan Bengalon Kabupaten Kutai Timur, Provinsi Kalimantan Timur (Thesis summary), UPN “Veteran” Yogyakarta. 8.

Santoso, H. (2002) Evaluasi Stabilitas Lereng dan Prediksi Volume Material Longsor Tambang Batubara PT. Tawabu Mineral Resource Provinsi Kalimantan Timur, Magister Teknik Geologi UGM (Thesis). 637.

Schneider, H.R. (1997) Definition and characterization of soil properties, in Proceedings XIV International Conference on Soil Mechanics and Geotechnical Engineering, Hamburg, Balkema, Rotterdam, 2271-2274.

Stearns, D. W. (1968) Certain aspects of fractures in naturally deformed rock, dalam Riecker, R. E. (ed.), NSF Advanced Science Seminar in Rock Mechanics, Air Force Cambridge Research Laboratories Special Report, Bedford, MA, 97-118.

Steffen, O.K.H., Terbrugge, P., Venter, J. (2008) A risk evaluation approach for pit slope design, Johannesburg: ARMA American Rock Mechanics Association.

Sukardi, Sikumbang, N., Umar, I., Sunaryo, R. (1995) Peta Geologi Lembar Sangatta, Kalimantan Skala 1:250.000, Bandung: Pusat Penelitian dan Pengembangan Geologi.

Tapia, A., Contreras, L.F., Jefferies, M., dan Steffen, O. (2007) Risk Evaluation of Slope Failure at the Chuquicamata Mine, in Proceedings of the 2007 International Symposium on Rock Slope Stability in Open Pit Mining and Civil Engineering, Perth, Australia, 1-12.

Ulusay, R. (2013) Harmonizing Engineering Geology With Rock Engineering For Assessing Rock Slope Stability, ISRM SINOROCK 2013, Shanghai.

Ulusay, R. (2019) Harmonizing Engineering Geology With Rock Engineering For Assessing Rock Slope Stability: A Review Of Current Practice, Geotehnika, Tuzla: Društvo za geotehniku u Bosni i Hercegovini, 1-16.

DOI: https://doi.org/10.22146/jag.76532