Stability Assessment of Rock Slopes at Former Quarries in Singapore

Authors

  • Kar Winn Myanmar Geologists Society Singapore, Blk 114, #08-150, Bedok Reservoir Road, Singapore
  • Chow Weng Lee Singapore Professional Engineer (Geotechnical), Singapore
  • Ong Perng Fey Sembcorp Specialised Construction Pte Ltd, 51 Changi Business Park Central 2, #06-12, S486066, Singapore
  • Htet Aung Linn Monolithic Pte Ltd, S596692, Singapore

Keywords:

Q-slope, Stability of rock slope, Scaling work, Slope angle, Geological Strength Index (GSI), Rockfall Risk Assessment for Quarries

Abstract

The redevelopment of abandoned quarry sites in Singapore requires precise rock slope stability assessments to ensure public safety. This study evaluated the applicability of the Q-slope and ROFRAQ methods to the Granite of Bukit Timah Centre. The Q-slope method for rock slope engineering was developed to enable engineering geologists and rock engineers to rapidly assess the stability of excavated rock slopes in the field and to make optimal adjustments to slope angles as rock mass conditions become apparent during construction of road cuts or benches. An empirical relationship between Q-slope and long-term stable slope angle is now supported by more than 600 case studies across 36 rock types on five continents. This paper presents the first application of the Q-slope method to abandoned quarry walls in Singapore. In Project 1, the rock slope was prepared for public viewing in its natural condition without artificial support; manual scaling was carried out to remove loose rock blocks. In Project 2, an assessment was conducted to evaluate the suitability of the rock slope for hiking. The study also investigated the relationship between Geological Strength Index (GSI) and Q-slope. Additionally, Rockfall Risk Assessment for Quarries (ROFRAQ), though initially developed for temperate climates, has been validated for use in tropical regions such as Singapore.

References

Alejano, L.R., Stockhausen, H.W., Alonson, E., Bastante, F.G., Oyanguren, P.R., 2008. ROFRAQ: A statistic based empirical method for assessing accident risk from rockfalls in quarries. International Journal of Rock Mechanics and Mining Sciences 45 (8), 1252-1272. https://doi.org/10.1016/j.ijrmms.2008.01.003.

Azarafza, M., Nanehkaran, Y.A., Rajabion, L., Akgun, H., Rahnamarad, J., Derakhshani, R., Raoof, A., 2020. Application of the modified Q-slope classification system for sedimentary rock slope stability assessment in Iran. Engineering Geology 264, 105-349. https://doi.org/10.1016/j.enggeo.2019.105349.

Azarafz, M., Kockar, M.K., Zhu, H.H., 2022. Correlations of SMR-Q-slope data in stability classification of discontinuous rock slope: a modified relationship considering the Iranian data. Geotechnical and Geological Engineering 40, 1751-1764. https://doi.org/10.1007/s10706-021-01991-w.

BCA, 2021. Building and Construction Authority Singapore, 2021. Singapore Geology, 173 pp, ISBN 978-0-85272-791-1.

Bar, N., Barton, N.R., 2016. Empirical slope design for hard and soft rocks using Q-slope. ARMA 16-384, Symposium of American Rock Mechanics Society.

Bar, N., Barton, N., 2017. The Q-Slope Method for Rock Slope Engineering. Rock Mechanics & Rock Engineering 50 (12), 3307-3322. https://doi.org/10.1007/s00603-017-1305-0.

Bar, N., Barton, N., 2018a. Rock slope design using Q-slope and geophysical survey data. Periodica Polytechnica Civil Engineering 62 (4), 893-900. https://doi.org/10.3311/PPci.12287.

Bar, N., Barton, N., 2018b. Q-Slope: An Empirical Rock Slope Engineering Approach in Australia. Australian Geomechanics Journal 53 (4), 73-86.

Bar, N., Barton, N., 2025. Q-slope: Rock Slope Engineering 10 years on. Rock Mechanics and Rock Engineering 58, 11453-11474. https://doi.org/10.1007/s00603-024-04064-5.

Bar, N., Mc Quillan, A., 2021. Q-slope and SSAM applied to excavated coal mine slopes. MethodsX 8 (101191). https://doi.org/10.1016/j.mex.2020.101191.

Barton, N., Lien, R., Lunde, J., 1974. Engineering classification of rock masses for the design of tunnel support. Rock Mechanics 6, 189-236. https://doi.org/10.1007/BF01239496.

Barton, N., Grimstad, E., 2014. Forty years with the Q-system in Norway and abroad. Fjellsprengningsteknikk, Bergmekanikk/Geoteknikk 2014, 4.1–4.25. Norsk Fjellteknisk Forening, Oslo, Norway.

Barton, N., Bar, N., 2015. Introducing the Q-slope method and its intended use within civil and mining engineering Case Studys. In: Schubert & Kluckner (ed), Future Development of Rock Mechanics: Proceedings of the ISRM Reg. Symp. Eurock 2015 & 64th Geomechanics Colloquium, Salzburg, 7-10 October 2015, pp 157-162.

Barton, N., Shen, B., Bar, N., 2018. Limited heights of vertical cliffs and mountain walls linked to fracturing in deep tunnels – Q-slope application if jointed slopes. Proc. XIX Congresso Brasileiro de Mecânica dos Solos e Engenharia Geotécnica Geotecnia e Desenvolvimento Urbano: COBRAMSEG 2018, Salvador, 28 August – 1 September 2018, ABMS, 13p.

Barton, N., Bar, N., 2019. The Q-slope method for rock slope engineering in faulted rocks and fault zones. In: Fontura et al. (eds), Rock mechanics for natural resources and infrastructure development, Proceedings of the 14th international congress on rock mechanics and rock engineerinh, Foz do Iguassu, 13-18 September 2019, pp 3424-3432.

Bieniawski, Z.T., 1976. Rock mass classification in rock engineering. In: Bieniawski (ed), Exploration for rock engineering: Proceedings of the symposium, Balkema, Cape Town, pp. 97-106.

Bieniawski, Z.T., 1989. Engineering rock mass classifications: a complete manual for engineers and geologists in mining, civil and petroleum engineering. Wiley, New York. P272.

Gupta, K., Gupta, S., Haris, P.M., Siddque, T., 2025. A multi-platform tool for modified Q-slope assessment in rock engineering: validation from the Himalayas. Geotechnical and Geological Engineering 43, 462. https://doi.org/10.1007/s10706-025-03440-4.

Hoek, E., Wood, D., Shah S., 1992. A modified Hoek-Brown criterion for jointed rock masses. Proc. Rock characterization, symp. Intl. Soc. Rock Mech.: Eurock 1992, (Ed. J.A. Hudson), 209-214. London: Brit. Geol. Soc.

Hoek, E., 1994. Strength of rock and rock masses. ISRM News Journal 2 (2), 4-16.

Hoek, E., Kaiser, P.K., Bawden, W.F., 1995. Support of underground excavations in hard rock. Rotterdam: Balkema, Rotterdam.

Jorda-Bordehore, L., Bar, N., Cano, M., Riquelme, A., Tomas, R., 2018. Stability assessment of rock slopes using empirical approaches: comparison between Slope Mass Rating and Q-slope. In: Proceedings of XIV Congreso International de Energiay Recursos Minerales and Slope Stability 2018, 10-13 April 2018, Seville, Spain, p 5 ionship considering the Iranian data. Geotechnical and Geological Engineering 40, 1751-1764. https://doi.org/10.1007/s10706-021-01991-w.

Kalpakci, V., Ozturk, S., Topal, T., Huvaj, N., 2016. Investigation of rock slope stability for an abandoned limestone quarry in Konya Turkey. Landslides and engineered slopes. Experience, Theory and Practice – Aversa et al. (Eds) Associazione Geotecnica Italiana, Rome, Italy, ISBN 978-1-138-02988-0.

Kouhdaragh, M., Azarafza, M., Derakhshani, R., 2022. A Q-slope based empirical method to stability assessment of mountain rock slopes in multiple faults zone: a case for North of Tabriz. MethodsX 9, 101718. https://doi.org/10.1016/j.mex.2022.101718.

Kolano, M., Cala, M., Stopkowicz, A., Olchowy P., Wendorff, M., 2015. Stability assessment of rock slopes in the former quarry of Wojciech Bednarski Park in Krakow – A case study. Applied Science 15, 7197. https://doi.org/10.3390/app15137197.

Laubscher, D.H., 1977. Geomechanics classification of jointed rock masses – mining applications. Trans Inst Metall Sect A Min Ind 93: A1-A8.

Laubscher, D.H., Jakubec, J., 2001. The MRMR rock mass classification for jointed rock masses, In: Hustrulid, Bullock (eds) Underground mining methods: engineering fundamentals and international case studies. AIME, New York, pp 474-481.

Mao, Y., Chen, L., Nanehkaran, Y.A., 2023. Fuzzy-based intelligent model for rapid rock slope stability analysis using Q-slope. Water 15 (16), 2949. https://doi.org/10.3390/w15162949.

Narimani, S., Davarpanah S.M., Bar, N., Torok, A., Vasarhelyi, B., 2023. Geological strength index relationships with the Q-system and Q-slope. Sustainability 15, 11233. https://doi.org/10.3390/su151411233.

Rocscience Inc., 2025. DIPS: Interactive Analysis of Orientation-Based Geological Data [Computer software]. Rocscience Inc., Toronto, Canada.

Romana, M., 1985. New adjustment ratings for application of Bieniawski classification to slopes. In: Proceedings of the ISRM international symposium in role of rock mechanics in excavations for mining and civil works, Zacatecas, pp. 49-53.

Romana M., 1995. The geomechanical classification SMR for slope correction. In: Proceedings of the 8th ISRM congress on Rock Mechanics 3, Tokyo, 25-29 September 1995, pp 1085-1092.

Saito, de Paula, M., Maion, A.V., Campanha, G.A.G., Castilho, L.M.N., Cunha, M.A., 2020. Q-slope and RHRS for the evaluation of highway rock slopes - Serra do Mar, Brazzil. In: Fontura et al. (eds), Rock mechanics for natural resources and infrastructure development, Proceedings of the 14th International Congress on Rock Mechanics & Rock Engg, Foz do Iguassu, 13-18 September 2019, p8

Song, Y., Xue, H., Meng, X., 2019. Evaluation method of slope stability based on the Q-slope system and BQ method. Bulletin of Engineering Geology and the Environment 78, 4865-4873. https://doi.org/10.1007/s10064-019-01459-5.

Siddique, T., Pradhan, S.P., Vishal, V., Singh, T.N., 2020. Applicability of Q-slope method in the Himalayan Road cut rock slopes and its comparison with CSMR. Rock Mechanics and Rock Engineering 53, 4509-4522. https://dot.org/10.1007/s00603-020-02176-2.

Tomas, R., Delgado, J., Seron, J.B., 2007. Modification of slope mass rating (SMR) by continuous functions. International Journal of Rock Mechanics and Mining Sciences 44, (7): 1062-1069. https://doi.org/10.1016/j.ijrmms.2007.02.004.

Tomas, R., Cuenca, A., Cano, M., Garcia-Barba, J., 2012. A graphical approach for slope mass rating (SMR). Eng Geol 124: 67-76. https://doi.org/10.1016/j.enggeo.2011.10.004.

Winn, K., Lee, C.W., Linn, H.A., 2022. Rock slope stability analysis of abandoned quarry wall applying Q-slope method: Singapore case study (AUSROCK Conference, Nov-Dec 2022, Melbourne, Australia).

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Published

2026-08-31

Issue

Vol. 8 No. 2 (2026): Vol. 8; Issue 2

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Articles

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Copyright (c) 2026 Kar Winn, Chow Weng Lee, Ong Perng Fey, Htet Aung Linn

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