Pit Slope Configuration for Open Pit Mining – A Case Study

Richard Gyebuni; Festus Kunkyin-Saadaari; Douglas Mensah-Kane

doi:doi:10.11648/j.ajset.20240902.14

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Pit Slope Configuration for Open Pit Mining – A Case Study

Richard Gyebuni^*

, Festus Kunkyin-Saadaari

, Douglas Mensah-Kane

Published in American Journal of Science, Engineering and Technology (Volume 9, Issue 2)

Received: 2 April 2024 Accepted: 3 May 2024 Published: 24 May 2024

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Abstract

To achieve stable pit wall slopes, it is imperative to obtain a fair knowledge of the rock mass characterisation before designing the pit. Insufficient knowledge of the competency of the country rock could lead to using unsupported slope configuration in the design process which can consequently lead to slope failure. In this study, the geomechnical properties of the Bremen-Nkosuo concession are analysed using Bieniawski’s classification scheme to determine the Rock Mass Rating (RMR) for defining safe pit slope configuration of the Nkosuo pit. The findings show that the rockmass are best described as ‘fair’ for the two main lithologies existing at the concession. Subsequently, localised adjustment factors are applied to the calculated RMR to arrive at Mining Rock Mass Ratings (MRMR). These MRMR values are correlated with 50 m fixed stack height and 1.2 safety factor to determine optimum Bench Slack Angle (BSA) of 54° and 57° for host sedimentary and granitic rocks respectively. For individual benches, optimum slope design configurations were 10 m, 800, and 6.6 m respectively for bench height, bench face angle and catch berm for metasedimentary rocks. Likewise, that for granitic formation were 10 m bench height, 800 face angle and 6.0 m catch berm width. These configurations are in conformance with mineral and mining regulations of Ghana. Slope stability assessment was performed which included Slope Mass Rating (SMR), Kinematic and Limit equilibrium analysis. From the analysis, multi-bench scale slope instability occurrence was found to be rare but single-double scale could be possible at the western wall of the planned pit with probability of failure of about 0.4. Presplit and trim shots perimeter blasting techniques are recommended to maintain the integrity of the final pit walls at certain areas.

Published in	American Journal of Science, Engineering and Technology (Volume 9, Issue 2)
DOI	10.11648/j.ajset.20240902.14
Page(s)	96-132
Creative Commons	This is an Open Access article, distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution and reproduction in any medium or format, provided the original work is properly cited.
Copyright	Copyright © The Author(s), 2024. Published by Science Publishing Group

Keywords

Pit Slope Stability, Bench, Berm, Rock Mass Characterisation

References

[1]	Read, J. and Stacey, P., 2023. Guidelines for Open Pit Slope Design, CRC Press, 510pp.
[2]	Wyllie, D. C. and Mah, C. W. Rock slope engineering, CRC Press, London 4^th ed., 2017, 456pp, https://orcid.org/10.1201/9781315274980
[3]	Pantelidis L. Rock slope stability assessment through rock mass classification systems. International Journal of Rock Mechanics and Mining Sciences. 2009, 46(2), 315-25.
[4]	Barton, N. R., Lien, R., & Lunde, J. Engineering classification of rock masses for the design of tunnel support. Rock Mechanics, 19746, (4), 189 - 239.
[5]	Hoek, E. Estimating Mohr-Coulomb friction and cohesion values from the Hoek-Brown failure criterion, International Journal of Rock Mechanics and Mining Sciences and Geomechanics Abstracts, 1994, 27(3), 227-229.
[6]	Bieniawski, Z. T. Proceedings Of The Symposium On Exploration For Rock Engineering, Johannesburg, 1-5 November 1976. Volumes 1 and 2. Publication of: AA Balkema Limited. 1976, 97-107.
[7]	Bieniawski, Z. T. Rock mass classifications in rock engineering, Proceedings of the Symposium on Exploration for Rock Engineering, Johannesburg, 1982, 97- 107.
[8]	Qazi, A. and Singh, K., 2023. Rock Mass Classification Techniques and Parameters: a Review. Journal of Mining and Environment, 14(1), pp. 155-178.
[9]	Laubscher, D. H. Design aspects and effectiveness of support systems in different mining conditions. Transactions of the Institution of Mining and Metallurgy, Sector A; United Kingdom. 1984, 70-81.
[10]	Romana M., Serón J. B. and Montalar, E. SMR Geomechanics classification: Application, experience and validation”, Proceedings of the 10th Congress of the International Society for rock mechanics, Technology roadmap for rock mechanics, South African Institute of Mining and Metallurgy, Merwe, 2003, 1-4.
[11]	Bieniawski, Z. T. Engineering rock mass classifications: a complete manual for engineers and geologists in mining, civil, and petroleum engineering. John Wiley & Sons; 1989, 272.
[12]	Romana, M., Tomás, R. and Seron, J. B., 2015, May. Slope Mass Rating (SMR) geomechanics classification: thirty years review. In ISRM Congress, Montreal, Canada (pp. ISRM-13CONGRESS). ISRM.
[13]	Romana, M. SMR classification, Proceedings of 7th ISRM International Congress on Rock Mechanics, Aachen, 1993, 16-20.
[14]	Anon. Minerals and Mining, Health, Safety and Technical Regulation Regulations of Ghana, 2012, LI2182, 2012, 75-78.
[15]	Dai, B., Li, D., Zhang, L., Liu, Y., Zhang, Z. and Chen, S., 2022. Rock mass classification method based on entropy weight–TOPSIS–Grey correlation analysis. Sustainability, 14(17), p. 10500.
[16]	Gibson, W., De Bruyn, I. A., and Walker, D. J. H. Stability of rock slopes in open pit mining and civil engineering situations, Proceedings of The South African Institute of Mining and Metallurgy International”, Considerations in the optimisation of bench face angle and berm width geometries for open pit mines, Symposium on Stability of Rock Slopes, Symposium Series S44, 2006, 557 – 579.
[17]	Douglas, K. J. The Shear Strength of Rock Masses”, PhD Thesis Dessertation, The University of New South Wales, School of Civil and Environmental Engineering, Sydney, 2002, 202pp.
[18]	Haines, A. and Terbrugge, P. J. Preliminary estimation of rock slope stability using rock mass classification systems, Proceedings of 7th International Society Rock Mechanics, Aachen. 2, 1991, 887- 892.
[19]	Hoek, E., and Bray, J. W. Rock Slope Engineering, The Institute of Mining and Metallurgy, London, 1981, 345.

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APA Style

Gyebuni, R., Kunkyin-Saadaari, F., Mensah-Kane, D. (2024). Pit Slope Configuration for Open Pit Mining – A Case Study. American Journal of Science, Engineering and Technology, 9(2), 96-132. https://doi.org/10.11648/j.ajset.20240902.14

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ACS Style

Gyebuni, R.; Kunkyin-Saadaari, F.; Mensah-Kane, D. Pit Slope Configuration for Open Pit Mining – A Case Study. Am. J. Sci. Eng. Technol. 2024, 9(2), 96-132. doi: 10.11648/j.ajset.20240902.14

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AMA Style

Gyebuni R, Kunkyin-Saadaari F, Mensah-Kane D. Pit Slope Configuration for Open Pit Mining – A Case Study. Am J Sci Eng Technol. 2024;9(2):96-132. doi: 10.11648/j.ajset.20240902.14

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@article{10.11648/j.ajset.20240902.14,
  author = {Richard Gyebuni and Festus Kunkyin-Saadaari and Douglas Mensah-Kane},
  title = {Pit Slope Configuration for Open Pit Mining – A Case Study
},
  journal = {American Journal of Science, Engineering and Technology},
  volume = {9},
  number = {2},
  pages = {96-132},
  doi = {10.11648/j.ajset.20240902.14},
  url = {https://doi.org/10.11648/j.ajset.20240902.14},
  eprint = {https://article.sciencepublishinggroup.com/pdf/10.11648.j.ajset.20240902.14},
  abstract = {To achieve stable pit wall slopes, it is imperative to obtain a fair knowledge of the rock mass characterisation before designing the pit. Insufficient knowledge of the competency of the country rock could lead to using unsupported slope configuration in the design process which can consequently lead to slope failure. In this study, the geomechnical properties of the Bremen-Nkosuo concession are analysed using Bieniawski’s classification scheme to determine the Rock Mass Rating (RMR) for defining safe pit slope configuration of the Nkosuo pit. The findings show that the rockmass are best described as ‘fair’ for the two main lithologies existing at the concession. Subsequently, localised adjustment factors are applied to the calculated RMR to arrive at Mining Rock Mass Ratings (MRMR). These MRMR values are correlated with 50 m fixed stack height and 1.2 safety factor to determine optimum Bench Slack Angle (BSA) of 54° and 57° for host sedimentary and granitic rocks respectively. For individual benches, optimum slope design configurations were 10 m, 800, and 6.6 m respectively for bench height, bench face angle and catch berm for metasedimentary rocks. Likewise, that for granitic formation were 10 m bench height, 800 face angle and 6.0 m catch berm width. These configurations are in conformance with mineral and mining regulations of Ghana. Slope stability assessment was performed which included Slope Mass Rating (SMR), Kinematic and Limit equilibrium analysis. From the analysis, multi-bench scale slope instability occurrence was found to be rare but single-double scale could be possible at the western wall of the planned pit with probability of failure of about 0.4. Presplit and trim shots perimeter blasting techniques are recommended to maintain the integrity of the final pit walls at certain areas.
},
 year = {2024}
}

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TY  - JOUR
T1  - Pit Slope Configuration for Open Pit Mining – A Case Study

AU  - Richard Gyebuni
AU  - Festus Kunkyin-Saadaari
AU  - Douglas Mensah-Kane
Y1  - 2024/05/24
PY  - 2024
N1  - https://doi.org/10.11648/j.ajset.20240902.14
DO  - 10.11648/j.ajset.20240902.14
T2  - American Journal of Science, Engineering and Technology
JF  - American Journal of Science, Engineering and Technology
JO  - American Journal of Science, Engineering and Technology
SP  - 96
EP  - 132
PB  - Science Publishing Group
SN  - 2578-8353
UR  - https://doi.org/10.11648/j.ajset.20240902.14
AB  - To achieve stable pit wall slopes, it is imperative to obtain a fair knowledge of the rock mass characterisation before designing the pit. Insufficient knowledge of the competency of the country rock could lead to using unsupported slope configuration in the design process which can consequently lead to slope failure. In this study, the geomechnical properties of the Bremen-Nkosuo concession are analysed using Bieniawski’s classification scheme to determine the Rock Mass Rating (RMR) for defining safe pit slope configuration of the Nkosuo pit. The findings show that the rockmass are best described as ‘fair’ for the two main lithologies existing at the concession. Subsequently, localised adjustment factors are applied to the calculated RMR to arrive at Mining Rock Mass Ratings (MRMR). These MRMR values are correlated with 50 m fixed stack height and 1.2 safety factor to determine optimum Bench Slack Angle (BSA) of 54° and 57° for host sedimentary and granitic rocks respectively. For individual benches, optimum slope design configurations were 10 m, 800, and 6.6 m respectively for bench height, bench face angle and catch berm for metasedimentary rocks. Likewise, that for granitic formation were 10 m bench height, 800 face angle and 6.0 m catch berm width. These configurations are in conformance with mineral and mining regulations of Ghana. Slope stability assessment was performed which included Slope Mass Rating (SMR), Kinematic and Limit equilibrium analysis. From the analysis, multi-bench scale slope instability occurrence was found to be rare but single-double scale could be possible at the western wall of the planned pit with probability of failure of about 0.4. Presplit and trim shots perimeter blasting techniques are recommended to maintain the integrity of the final pit walls at certain areas.

VL  - 9
IS  - 2
ER  -

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Author Information

Richard Gyebuni

Department of Mining Engineering, University of Mines and Technology, Tarkwa, Ghana

Contact Email

http://orcid.org/0000-0002-9957-5351
Festus Kunkyin-Saadaari

Department of Mining Engineering, University of Mines and Technology, Tarkwa, Ghana

Contact Email

http://orcid.org/0000-0002-8202-2021
Douglas Mensah-Kane

Mineral Resource Department, Perseus Mining, Cantonments, Ghana

Contact Email

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APA Style

Gyebuni, R., Kunkyin-Saadaari, F., Mensah-Kane, D. (2024). Pit Slope Configuration for Open Pit Mining – A Case Study. American Journal of Science, Engineering and Technology, 9(2), 96-132. https://doi.org/10.11648/j.ajset.20240902.14

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ACS Style

Gyebuni, R.; Kunkyin-Saadaari, F.; Mensah-Kane, D. Pit Slope Configuration for Open Pit Mining – A Case Study. Am. J. Sci. Eng. Technol. 2024, 9(2), 96-132. doi: 10.11648/j.ajset.20240902.14

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AMA Style

Gyebuni R, Kunkyin-Saadaari F, Mensah-Kane D. Pit Slope Configuration for Open Pit Mining – A Case Study. Am J Sci Eng Technol. 2024;9(2):96-132. doi: 10.11648/j.ajset.20240902.14

Copy | Download

@article{10.11648/j.ajset.20240902.14,
  author = {Richard Gyebuni and Festus Kunkyin-Saadaari and Douglas Mensah-Kane},
  title = {Pit Slope Configuration for Open Pit Mining – A Case Study
},
  journal = {American Journal of Science, Engineering and Technology},
  volume = {9},
  number = {2},
  pages = {96-132},
  doi = {10.11648/j.ajset.20240902.14},
  url = {https://doi.org/10.11648/j.ajset.20240902.14},
  eprint = {https://article.sciencepublishinggroup.com/pdf/10.11648.j.ajset.20240902.14},
  abstract = {To achieve stable pit wall slopes, it is imperative to obtain a fair knowledge of the rock mass characterisation before designing the pit. Insufficient knowledge of the competency of the country rock could lead to using unsupported slope configuration in the design process which can consequently lead to slope failure. In this study, the geomechnical properties of the Bremen-Nkosuo concession are analysed using Bieniawski’s classification scheme to determine the Rock Mass Rating (RMR) for defining safe pit slope configuration of the Nkosuo pit. The findings show that the rockmass are best described as ‘fair’ for the two main lithologies existing at the concession. Subsequently, localised adjustment factors are applied to the calculated RMR to arrive at Mining Rock Mass Ratings (MRMR). These MRMR values are correlated with 50 m fixed stack height and 1.2 safety factor to determine optimum Bench Slack Angle (BSA) of 54° and 57° for host sedimentary and granitic rocks respectively. For individual benches, optimum slope design configurations were 10 m, 800, and 6.6 m respectively for bench height, bench face angle and catch berm for metasedimentary rocks. Likewise, that for granitic formation were 10 m bench height, 800 face angle and 6.0 m catch berm width. These configurations are in conformance with mineral and mining regulations of Ghana. Slope stability assessment was performed which included Slope Mass Rating (SMR), Kinematic and Limit equilibrium analysis. From the analysis, multi-bench scale slope instability occurrence was found to be rare but single-double scale could be possible at the western wall of the planned pit with probability of failure of about 0.4. Presplit and trim shots perimeter blasting techniques are recommended to maintain the integrity of the final pit walls at certain areas.
},
 year = {2024}
}

Copy | Download

TY  - JOUR
T1  - Pit Slope Configuration for Open Pit Mining – A Case Study

AU  - Richard Gyebuni
AU  - Festus Kunkyin-Saadaari
AU  - Douglas Mensah-Kane
Y1  - 2024/05/24
PY  - 2024
N1  - https://doi.org/10.11648/j.ajset.20240902.14
DO  - 10.11648/j.ajset.20240902.14
T2  - American Journal of Science, Engineering and Technology
JF  - American Journal of Science, Engineering and Technology
JO  - American Journal of Science, Engineering and Technology
SP  - 96
EP  - 132
PB  - Science Publishing Group
SN  - 2578-8353
UR  - https://doi.org/10.11648/j.ajset.20240902.14
AB  - To achieve stable pit wall slopes, it is imperative to obtain a fair knowledge of the rock mass characterisation before designing the pit. Insufficient knowledge of the competency of the country rock could lead to using unsupported slope configuration in the design process which can consequently lead to slope failure. In this study, the geomechnical properties of the Bremen-Nkosuo concession are analysed using Bieniawski’s classification scheme to determine the Rock Mass Rating (RMR) for defining safe pit slope configuration of the Nkosuo pit. The findings show that the rockmass are best described as ‘fair’ for the two main lithologies existing at the concession. Subsequently, localised adjustment factors are applied to the calculated RMR to arrive at Mining Rock Mass Ratings (MRMR). These MRMR values are correlated with 50 m fixed stack height and 1.2 safety factor to determine optimum Bench Slack Angle (BSA) of 54° and 57° for host sedimentary and granitic rocks respectively. For individual benches, optimum slope design configurations were 10 m, 800, and 6.6 m respectively for bench height, bench face angle and catch berm for metasedimentary rocks. Likewise, that for granitic formation were 10 m bench height, 800 face angle and 6.0 m catch berm width. These configurations are in conformance with mineral and mining regulations of Ghana. Slope stability assessment was performed which included Slope Mass Rating (SMR), Kinematic and Limit equilibrium analysis. From the analysis, multi-bench scale slope instability occurrence was found to be rare but single-double scale could be possible at the western wall of the planned pit with probability of failure of about 0.4. Presplit and trim shots perimeter blasting techniques are recommended to maintain the integrity of the final pit walls at certain areas.

VL  - 9
IS  - 2
ER  -

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