Numerical Modelling of Shear Zone and Its Implications on Slope Instability at Letšeng Diamond Open Pit Mine, Lesotho
Rock mass damage due to shear tectonic activity has been investigated largely in geoscience where fluid transport is of major interest. However, little has been studied on the effect of shear zones on rock mass behavior and its impact on stability of rock slopes. At Letšeng Diamonds open pit mine in Lesotho, the shear zone composed of sheared kimberlite material, calcite and altered basalt is forming part of the haul ramp into the main pit cut 3. The alarming rate at which the shear zone is deteriorating has triggered concerns about both local and global stability of pit the walls. This study presents the numerical modelling of the open pit slope affected by shear zone at Letšeng Diamond Mine (LDM). Analysis of the slope involved development of the slope model by using a two-dimensional finite element code RS2. Interfaces between shear zone and host rock were represented by special joint elements incorporated in the finite element code. The analysis of structural geological mapping data provided a good platform to understand the joint network. Major joints including shear zone were incorporated into the model for simulation. This approach proved successful by demonstrating that continuum modelling can be used to evaluate evolution of stresses, strain, plastic yielding and failure mechanisms that are consistent with field observations. Structural control due to geological shear zone structure proved to be important in its location, size and orientation. Furthermore, the model analyzed slope deformation and sliding possibility along shear zone interfaces. This type of approach can predict shear zone deformation and failure mechanism, hence mitigation strategies can be deployed for safety of human lives and property within mine pits.
Digital Object Identifier (DOI): doi.org/10.5281/zenodo.1129892Procedia APA BibTeX Chicago EndNote Harvard JSON MLA RIS XML ISO 690 PDF Downloads 971
 T. C. Badger, Fracturing within anticlines and its kinematic control on slope stability. Environmental & Engineering Geoscience. 2002;8(1):19-33.
 D. C. Bowen, R. D. Ferraris, C.E. Palmer, J. D. Ward. On the unusual characteristics of the diamonds from Letšeng-la-Terae kimberlites, Lesotho. Lithos. 2009; 112:767-74.
 M. Lephatsoe, E. Hingston, M. Ferentinou, N. Lefu. Kinematic Analyses of the Western Pitwall of the Main Pit in the Letseng Diamond Mine, Lesotho. ISRM Regional Symposium-EUROCK 2014; International Society for Rock Mechanics; 2014.
 F. Reichhardt, M. Lynn. Lemphane kimberlite technical report. Ni 43-101 Independent Technical Report on the Lephane Kimberlite Project, Lesotho. 2010;19-21; unpublished.
 A. Madowe. The mine planning process for an open-pit diamond mining operation-a case study on Letseng diamond mine in Lesotho. Journal of the Southern African Institute of Mining and Metallurgy. 2013;113(7):547-54.
 R. Shor, R. Weldon, A. Janse, C. M. Breeding, S. B. Shirey. Letšeng's Unique Diamond Proposition. Gems & Gemology. 2015;51(3).
 S. Laws, E. Eberhardt, S. Loew, F. Descoeudres. Geomechanical properties of shear zones in the Eastern Aar Massif, Switzerland and their implication on tunnelling. Rock Mech Rock Eng. 2003;36(4):271-303.
 D. Wise, D. Dunn, J. Engelder, P. Geiser, R. Hatcher, S. Kish. Fault-related rocks: suggestions for terminology. Geology. 1984;12(7):391-4.
 S. Vearncombe, J. R. Vearncombe. Tectonic controls on kimberlite location, southern Africa. J Struct Geol. 2002;24(10):1619-25.
 S.D. Priest. Discontinuity analysis for rock engineering. Springer Science & Business Media; 2012.
 D. Laubscher, J. Jakubec. The MRMR rock mass classification for jointed rock masses. Underground Mining Methods: Engineering Fundamentals and International Case Studies, WA Hustrulid and RL Bullock (eds) Society of Mining Metallurgy and Exploration, SMME. 2001:475-81.
 Z. T. Bieniawski, 1973. Engineering classification of jointed rock masses. Trans S. Afr. Inst. Civ. Engrs 15, 335-344.
 J. A. Hudson, S. D. Priest, Discontinuities and Rock Mass Geometry, International Journal of Rock Mechanics and Mining Sciences, 1979: Vol: 16, Pages: 339-362, ISSN: 0148-9062.
 D. U. Deere, R. Miller. Engineering classification and index properties for intact rock. 1966.
 E. Hoek, P. Marinos. Predicting tunnel squeezing problems in weak heterogeneous rock masses. Tunnels and tunnelling international. 2000;32(11):45-51.
 E. Hoek, T. Carter, M. Diederichs. Quantification of the geological strength index chart. 47th US Rock Mechanics/Geomechanics Symposium; American Rock Mechanics Association; 2013.
 E. Hoek, E.T. Brown. Practical estimates of rock mass strength. Int J Rock Mech Min Sci. 1997;34(8):1165-86.
 E. Hoek, C. Carranza-Torres, B. Corkum. Hoek-Brown failure criterion-2002 edition. Proceedings of NARMS-Tac. 2002;1:267-73.
 D. Laubscher D. A geomechanics classification system for the rating of rock mass in mine design. JS Afr.Inst.Metall. 1990;90(10):267-73.
 P. Wriggers. Finite element algorithms for contact problems. Archives of Computational Methods in Engineering. 1995;2(4):1-49.
 S. Bandis, A. Lumsden, N. Barton. Fundamentals of rock joint deformation. International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts; Elsevier; 1983.
 https://www.rocscience.com/ Accessed on 27/11/2016
 Y. Zheng, X. Tang, S. Zhao, C. Deng, W. Lei. Strength reduction and step-loading finite element approaches in geotechnical engineering. Journal of Rock Mechanics and Geotechnical Engineering. 2009 10/26;1(1):21-30.