Institute of the Earth’s Crust, Siberian Branch, Russian Academy of Sciences, Irkutsk, Russia

Serebryakov Е. V., Junior Researcher, Candidate of Geological and Mineralogical Sciences, serebryakov.e.v@mail.ru
Gladkov A. S., Head of Laboratory, Chief, Candidate of Geological and Mineralogical Sciences

Mining Society of Catoca, Luanda, Angola
Felix J. T., Director of Production, Candidate of Geological and Mineralogical Sciences
Karpenko M. A., Chief Geologist

The Catoca open pit, which develops the kimberlite pipe of the same name, is located in the northeast of the Republic of Angola. The project of mining from the actual elevation of +840 m downward included a significant increase in the heights and slope angles of the benches. In this connection, it became necessary to describe comprehensively the structural defects in the gneiss rock mass to accommodate the ultimate pit limit. To this effect, 13 boreholes were drilled in gneiss with a view to performing the acoustic and optical televiewer logging. The interpretation of the obtained data points out two dominant systems of joints in the open pit mine field, which indicates the unity of the structure and lithology of the deposit. Based on the obtained characteristic of jointing and using the project data on the open pit design, the kinematic analysis was performed. The increased potential of the inplane slip-type failure structures was found for the northern and southern pitwall benches. The northern and eastern pitwall is favorable for the development of the V-type slip deformation. The probabilistic kinetic analysis by the method of limiting equilibrium was carried out within the allocated sectors of the open pit; the analysis exhibited the high factor of stability of the actual pitwall design. Increase in the angle and height of the benches will initiate inadmissibly hazardous areas on the southern and eastern pitwall in terms of the deformation types considered. The risk of the impact on personnel and equipment in the hazardous areas can be reduced to an acceptable level through the implementation of instrumental monitoring. On the basis of the obtained FoS and PoF ratios, the design solutions adopted for the ultimate pitwall limit design in the Catoca diamond mine can be conditionally assumed as an optimum. Maximization of economic effect of mining is achievable through the increase in the slope angles on the northern and southern pitwall up to 70°. In this case, the high probability of the slope instability in this design should be profoundly addressed by the risk management.

1. Read J., Stacey P. (Eds.). Guidelines for open pit slope design. Translated from English. Yekaterinburg : Pravoved, 2015. 544 p.
2. Rylnikova M. V., Zoteev O. V., Nikiforova I. L. Development of the regulatory framework to provide the stability of pitwalls and benches of quarries, opencast mines and spoil dumps. Gornaya promyshlennost. 2018. No. 3(139). pp. 95–98.
3. Pervov V. A., Somov S. V., Korshunov A. V., Dulapchiy E. V., Feliks Zh. T. The Catoca kimberlite pipe, Republic of Angola : Paleovolcanic modeling. Gеologiya rudnyh mеstorozhdеnij. 2011. Vol. 53, No 4. pp. 330–345.
4. Zinchuk N. N., Stegnitskiy Yu. B. Features of the weathering crust of the kimberlites of North-East Angola. Proceedings of Voronezh State University. Series: Geology. 2020. No. 2. pp. 6–19.
5. McKenna G. T. C., Roberts-Kelly S. L. Televiewer imaging of boreholes; benefits and considerations for interpretation in the absence of physical rock core. Australian Geomechanics Society. 2016. pp. 291–296.
6. Benedicto A., Harrison G., Eccles B., Ledru P. Advanced Use of Borehole Acoustic Televiewer (ATV) for Structural Interpretation of Unconformity-Related Uranium Deposits. Economic Geology. 2021. Vol. 116, No. 6. pp. 1435–1453.
7. Dempers G., Nguyen T., Seymour C. Advanced methodology for geotechnical televiewer interpretation. Civil Engineering. 2019. Vol. 27, No. 3. pp. 36–43.
8. Terzaghi R. D. Sources of Error in Joint Surveys. Géotechnique. 1965. Vol. 15, Iss. 3. pp. 287–304.
9. Tang H., Zhang J., Huang L., Yan Ch., Hu S. et al. Correction of Line-Sampling Bias of Rock Discontinuity Orientations Using a Modified Terzaghi Method. Advances in Civil Engineering. 2018. pp. 1–9. DOI: 10.1155/2018/1629039
10. Lunina O. V., Gladkov A. S., Gladkochub D. P., João F., Karpenko M. A. et al. The evolution of the crustal stress state of the Catoca kimberlite pipe area (Northeastern Angola). Geodynamics & tectonophysics. 2018. Vol. 9. No. 3. pp. 827–854.
11. Bushkov V. K. Use of kinematic stability analysis in substantiation of basic wall design parameters for open pits. GIAB. 2018. No. 10. pp. 30–42.
12. Goodman R. E. Methods of geological engineering in discontinuous rocks. San Francisco : West Publishing, 1976. 472 p.
13. Markland J. T. A useful technique for estimating the stability of rock slopes when the rigid wedge sliding type of failure is expected. Imperial College Rock Mechanics Research Report. 1972. No. 19. 10 p.
14. Spirin V. I., Livinskiy I. S., Hormazabal A. Risk-based optimization of open pit slopes. Izvestija Tulskogo Gosudarstvennogo Universiteta. Nauki o Zemle. 2019. No. 3. pp. 317–331.
15. Obregon C., Mitri H. Probabilistic approach for open pit bench slope stability analysis—A mine case study. International Journal of Mining Science and Technology. 2019. Vol. 29, Iss. 4. pp. 629–640.
16. Fleurisson J-A. Slope design and implementation in open pit mines: Geological and geomechanical approach. Procedia Engineering. 2012. Vol. 46. pp. 27–38.
17. Christian J. T. Geotechnical engineering reliability: How well do we know what we are doing? Journal of Geotechnical and Geoenvironmental Engineering. 2004. Vol. 130, Iss. 10. pp. 985–1003.
18. Sullivan T. D. Pit slope design and risk—A view of the current state of the art. Proceedings of International Symposium on Stability of Rock Slopes in Open Pit Mining and Civil Engineering. South African Institute of Mining and Metallurgy. Johannesburg. 2006. pp. 51–78.
19. Priest S. D., Brown E. T. Probabilistic stability analysis of variable rock slopes. Transactions of Institution of Mining and Metallurgy. Section A: Mining Industry. 1983. Vol. 92. pp. A1-A12.
20. Kumar A., Rathee R. Monitoring and evaluating of slope stability for setting out of critical limit at slope stability radar. International Journal of Geo-Engineering. 2017. Vol. 8(18). pp. 1–16.
21. Ulusay R. The ISRM suggested methods for rock characterization, testing and monitoring: 2007–2014. Bulletin of Engineering Geology and the Environment. 2015. Vol. 74. pp. 1499–1500.