Numerical Analysis of Slope Stability Due to Excavation of Diversion Tunnel at Pamukkulu Dam Site, Indonesia

https://doi.org/10.22146/jag.57658

Wakhid Khoiron Nugroho(1), I Gde Budi Indrawan, Dr.(2*), Nugroho Imam Setiawan(3)

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

Abstract


Located in the Takalar Regency of South Sulawesi Province, the Pamukkulu Dam is planned to use a tunnel type as its diversion structure. One of the critical parts in the tunnel construction is the stability of portal slopes. This research aimed to estimate the effect of tunnel excavation on the stability of the portal inlet and outlet slopes under static and earthquake loads by using the finite element method. The slope stability analyses were carried out under conditions of prior to and after tunnel excavation. The input parameters used were laboratory test results in the forms of index properties and mechanical properties taken from rock core drilling samples, completed with the rock mass quality parameters based on the Geological Strength Index (GSI) classification. The Mohr-Coulomb failure criterion was used to model strength of the soil, while the Generalized Hoek-Brown failure criterion was used to model strength of the rocks. The results of rock cores analysis using the GSI method showed that the inlet tunnel slope consisted of four types of materials, namely residual soil, fair quality of basalt lava, good quality of basalt lava, and very good quality of basalt lava. Meanwhile, the outlet portal slope consisted of three types of materials, namely residual soil, good quality basalt lava, and very good quality basalt lava. The calculated horizontal seismic coefficient for the pseudo-static slope stability analysis was 0.0375. The analysis results of slope stability in the Y1 inlet section had a critical Strength Reduction Factor (SRF) value of 2.35 in a condition prior to the tunnel excavation and a critical SRF value of 2.34 after the tunnel excavation. The Y2 outlet section had a critical SRF value of 13.27 in a condition before tunnel excavation and a critical SRF value of 5.55 after the tunnel excavation. The earthquake load addition at the Y1 inlet section showed a critical SRF value of 2.05, both before and after the tunnel excavation. The Y2 outlet section showed a critical SRF value of 11.49 before the tunnel excavation and a critical SRF value of 5.54 after the tunnel excavation. The numerical analysis results showed that earthquake load reduced critical SRF values of the slopes. At the Y1 inlet section, the tunnel excavation did not have a significant effect on slope stability. It was demonstrated by an extremely small decrease in a critical SRF value of 0.43% for a condition without an earthquake load and an unchanged critical SRF in a condition with an earthquake load. At the Y2 outlet section, the tunnel excavation had a more significant effect on the slope stability. It was exhibited by the decrease in the critical SRF value of 58.18% in a condition without an earthquake load and a decrease in the critical SRF value of 51.78% in a condition with an addition of an earthquake load. However, the analysis of slope stability for both sections showed that all design slopes were above the required allowable safety factor value.

Keywords


diversion tunnel; finite element; GSI; slope stability; Pamukkulu Dam

Full Text:

PDF


References

BBWS Pompengan-Jeneberang. (2016). Sertifikasi Desain Bendungan Pamukkulu. Makassar.

BSN (2017). SNI 8460:2017. Persyaratan Perancangan Geoteknik. Jakarta.

Hoek, E., Carter, T., & Diederichs, M. (2013). Quantification of the Geological Strength Index Chart. US Rock Mechanics /Geomechanics Symposium. San Francisco: June 23-26, 2013.

ISRM. (1978). Suggested Methods for The Quantitative Description of Discontinuities in Rock Masses: International Society for Rock Mechanics. International Journal of Rock Mechanics and Mining Science & Geomechanics Abstracts, 368.

Marinos, P., & Hoek, E. (2001). Estimating the geotechnical properties of heterogeneous rock masses such as flysch. Bulletin of the Engineering Geology & the Environment (IAEG), 60, 85-92.

Nugroho, W. (2020). Evaluasi Kondisi Geologi Teknik dan Analisis Kestabilan Terowongan Pengelak Bendungan Pamukkulu Provinsi Sulawesi Selatan. Yogyakarta: Unpublished.

National Earthquake Research Center. (2017). Peta Sumber dan Bahaya Gempabumi Indonesia . Jakarta: Kementerian Pekerjaan Umum dan Perumahan Rakyat.

Sivakugan, N; Shukla, S.K; Das, B.M. (2013). Rocks Mechanics an Introduction. New York: CRC Press.



DOI: https://doi.org/10.22146/jag.57658

Article Metrics

Abstract views : 682 | views : 554

Refbacks

  • There are currently no refbacks.


Copyright (c) 2022 Wakhid Khoiron Nugroho, I Gde Budi Indrawan, Dr., Nugroho Imam Setiawan

Journal of Applied Geology Indexed by:

 

Creative Commons License
This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.