International Journal of Mining and Geo-Engineering

International Journal of Mining and Geo-Engineering

Numerical approach for designing support systems for underground excavations in serpentinite under squeezing ground conditions: the case of the Bou-Azzer mine, morocco

Articles in Press

Document Type : Research Paper

Authors
Anas Driouch 1
Redouane Oubah 1
Mohamed Bhilisse 2
Abdelaziz Lahmili 1
Latifa Ouadif 1
1 Laboratory of Applied Geophysics, Geotechnics, Engineering Geology and Environment, Mohammadia School of Engineers, Mohammed V University in Rabat, Morocco.
2 Faculty of Sciences Semlalia, Cadi Ayyad University in Marrakech, Morocco.
10.22059/ijmge.2026.404369.595325
Abstract
The instability of underground excavations developed in serpentinite rock masses at the Bou-Azzer cobalt mine in Morocco has long been a critical concern for geotechnical engineering. The challenges encountered in two previous strategic projects, at depths of 360 meters and 510 meters, were mainly attributed to stress conditions exceeding the rock strength, leading to significant reductions in the cross-sectional area of the excavations and severe deformation of the installed support systems. Conventional empirical support design approaches applied at the mine have shown clear limitations when dealing with serpentinite rock masses. Another limitation of these methods is that they do not allow for the assessment of support system performance and deformation control to improve the stability of such deep excavations. The primary objective of this study is to develop a reliable support system capable of ensuring a safe working environment for personnel and equipment through numerical modeling of excavation behavior at a depth of 540 meters, corresponding to the new mine extension. The adopted methodology is based on detailed two-dimensional finite element modeling, explicitly accounting for the variability in the mechanical behavior of the serpentinite rock mass and its interaction with the proposed support systems through a site-specific analysis. Numerical simulations were conducted for different serpentinite types under two analysis scenarios: excavations during development and excavations with installed support. The results indicate that maximum displacements are critically high in type 4 serpentinite and remain substantial in type 1 serpentinite. By contrast, moderate displacement values were observed in type 2 and type 3 serpentinites. However, once the proposed support measures were implemented, the maximum displacements were reduced to acceptable limits with respect to the excavation span and height, and the safety factors improved to between 1.10 and 1.30 for the crown and from 1.10 to 1.60 for the sidewall. Numerical modeling has proven to be an effective decision-support tool for deep underground excavations in complex rock conditions. The findings of this study provide a practical and reliable basis for designing support systems in deep mining environments, with approaches that can be extended to other sites facing similar geotechnical challenges.



Keywords
Keywords: Underground mining
Serpentinite
Squeezing ground
Numerical modeling
Support system
Subjects
[1]        A. Driouch, L. Ouadif, A. Lahmili, et M. A. Belmi, « Evaluation of the Compression Potential of Serpentine Rock Masses of the Bou Azzer Mining District in the Central Anti-Atlas of Morocco », Mining, Metallurgy & Exploration, vol. 39, no 1, p. 189‑200, févr. 2022, doi: 10.1007/s42461-021-00517-5.
[2]        J. Hadjigeorgiou et E. Karampinos, « Design tools for squeezing ground conditions in hard rock mines’, in J Wesseloo (ed.), Deep Mining 2017: Proceedings of the Eighth International Conference on Deep and High Stress Mining, Australian Centre for Geomechanics, Perth, pp. 693-705, ». Consulté le: 28 juillet 2025.
[3]        F. Mercier-Langevin et J. Hadjigeorgiou, « Towards a better understanding of squeezing potential in hard rock mines », Mining Technology, vol. 120, no 1, p. 36‑44, 2011.
[4]        F. Mercier-Langevin et D. Wilson, « Lapa Mine – ground control practices in extreme squeezing ground », in Proceedings of the Seventh International Symposium on Ground Support in Mining and Underground Construction, Australian Centre for Geomechanics, Perth, 2013, p. 119‑131. doi: 10.36487/ACG_rep/1304_06_Mercier-Langevin.
[5]        Y. Potvin et J. Hadjigeorgiou, « Ground support strategies to control large deformations in mining excavations », Journal of the Southern African Institute of Mining and Metallurgy, vol. 108, no 7, p. 397‑404, juill. 2008.
[6]        N. Barton, R. Lien, et J. Lunde, « Engineering classification of rock masses for the design of tunnel support », Rock Mechanics, vol. 6, no 4, p. 189‑236, déc. 1974, doi: 10.1007/BF01239496.
[7]        Z. T. Bieniawski, Engineering Rock Mass Classifications: A Complete Manual for Engineers and Geologists in Mining, Civil, and Petroleum Engineering. John Wiley & Sons, 1989.
[8]        D. U. Deere, R. B. Peck, H. W. Parker, J. E. Monsees, et B. Schmidt, « Design of Tunnel Support Systems, High Res. Rec., No. 339, pp. 26-33. », 1970.
[9]        A. Palmstrom, « Characterising the strength of rock mass for use in design of underground structures, Design and construction of underground structures, Volume 43-52: New Delhi. » 1995.
[10]      A. Driouch, R. Oubah, A. Lahmili, et L. Ouadif, « Empirical methods for support system design in deep serpentinite excavations: A critical evaluation », Journal of Sustainable Mining, vol. 24, no 4, p. 551‑564, oct. 2025, doi: 10.46873/2300-3960.1473.
[11]      J. M. Galvin, Ground Engineering - Principles and Practices for Underground Coal Mining. Cham: Springer International Publishing, 2016. doi: 10.1007/978-3-319-25005-2.
[12]      M. Amirkhani, M. Bahaaddini, A. Kargar, et A. Hekmatnejad, « Sensitivity Analysis of Tunnel Excavation Damage Zone in Jointed Rock Masses: A DFN-DEM Approach », Journal of Mining and Environment, juin 2025, doi: 10.22044/jme.2025.16037.3091.
[13]      A. Driouch, L. Ouadif, A. Lahmili, M. A. Belmi, et K. Benjmel, « Geotechnical modeling of the method for mining cobalt deposits at the Bou Azzer Mine, Morocco », Min. miner. depos., vol. 17, no 1, p. 51‑58, mars 2023, doi: 10.33271/mining17.01.051.
[14]      K. Esmaieli et J. Hadjigeorgiou, « Application of DFN–DEM modelling in addressing ground control issues at an underground mine, Mining Technology, 124:3, 138-149 »,. Consulté le: 28 juillet 2025. DOI: 10.1179/1743286315Y.0000000013
[15]      P. R. Helm, C. T. Davie, et S. Glendinning, « Numerical modelling of shallow abandoned mine working subsidence affecting transport infrastructure », Engineering Geology, vol. 154, p. 6‑19, févr. 2013, doi: 10.1016/j.enggeo.2012.12.003.
[16]      G. Huang, P. H. S. W. Kulatilake, S. Shreedharan, S. Cai, et H. Song, « 3-D discontinuum numerical modeling of subsidence incorporating ore extraction and backfilling operations in an underground iron mine in China », International Journal of Mining Science and Technology, vol. 27, no 2, p. 191‑201, mars 2017, doi: 10.1016/j.ijmst.2017.01.015.
[17]      C. Zheng et al., « Study on the instability of surrounding rock and optimization of support systems in fault-crossing tunnels », Bull Eng Geol Environ, vol. 84, no 2, p. 71, janv. 2025, doi: 10.1007/s10064-024-04065-2.
[18]      M. Zoorabadi, « Numerical modelling of the underground roadways in coal mines– uncertainties caused by use of empirical-based downgrading methods and in situ stresses », Journal of Mining and Environment, vol. 9, no 3, p. 593‑604, juill. 2018, doi: 10.22044/jme.2018.6633.1485.
[19]      T. Zvarivadza, « Numerical Modelling Application in the Management of Deep Mining Excavation Stresses: An Illustrative Study », Mining, vol. 3, no 4, Art. no 4, déc. 2023, doi: 10.3390/mining3040040.
[20]      E. Karampinos, J. Hadjigeorgiou, et P. Turcotte, « Discrete Element Modelling of the Influence of Reinforcement in Structurally Controlled Squeezing Mechanisms in a Hard Rock Mine », Rock Mech Rock Eng, vol. 49, no 12, p. 4869‑4892, déc. 2016, doi: 10.1007/s00603-016-1080-3.
[21]      A. Naeem et L. Ke-gang, « Exploring Ground Behavior in Underground Excavations Under Squeezing Stress Conditions », 2024, doi: https://doi.org/10.22044/jme.2024.14198.2644.
[22]      P. Yadav et S. Sharan, « Numerical Investigation of Squeezing in Underground Hard Rock Mines », Rock Mech Rock Eng, vol. 52, no 4, p. 1211‑1229, avr. 2019, doi: 10.1007/s00603-018-1632-9.
[23]      M. Leblanc, « The late Proterozoic ophiolites of Bou Azzer (Morocco): evidence for Pan-African plate tectonics », in Developments in Precambrian Geology, vol. 4, Elsevier, 1981, p. 435‑451.
[24]      R. Bousquet, R. El Mamoun, O. Saddiqi, B. Goffé, A. Möller, et A. Madi, « Mélanges and ophiolites during the Pan-African orogeny: the case of the Bou-Azzer ophiolite suite (Morocco) | Geological Society, London, Special Publications, 297, p. 233–247. » Consulté le: 30 juillet 2025. https://doi.org/10.1144/sp297.11
[25]      A. Saquaque, H. Admou, J. Karson, K. Hefferan, et I. Reuber, « Precambrian accretionary tectonics in the Bou Azzer-El Graara region, Anti-Atlas, Morocco », Geology, vol. 17, no 12, p. 1107‑1110, déc. 1989, doi: 10.1130/0091-7613(1989)017%3C1107:PATITB%3E2.3.CO;2.
[26]      D. Gasquet, G. Levresse, A. Cheilletz, M. R. Azizi-Samir, et A. Mouttaqi, « Contribution to a geodynamic reconstruction of the Anti-Atlas (Morocco) during Pan-African times with the emphasis on inversion tectonics and metallogenic activity at the Precambrian–Cambrian transition », Precambrian Research, vol. 140, no 3, p. 157‑182, nov. 2005, doi: 10.1016/j.precamres.2005.06.009.
[27]      A. Souleimani et al., « Notice explicative carte géologique Maroc (1/50 000), feuille Al Glo’a », 2013.
[28]      O. Blein et al., « Geochronological constraints on the polycyclic magmatism in the Bou Azzer-El Graara inlier (Central Anti-Atlas Morocco) », Journal of African Earth Sciences, vol. 99, p. 287‑306, nov. 2014, doi: 10.1016/j.jafrearsci.2014.04.021.
[29]      J. L. Bodinier, C. Dupuy, et J. Dostal, « Geochemistry of precambrian ophiolites from Bou Azzer, Morocco », Contributions to Mineralogy and Petrology, vol. 87, no 1, p. 43‑50, 1984.
[30]      J. D. Inglis, R. S. D’Lemos, S. D. Samson, et H. Admou, « Geochronological Constraints on Late Precambrian Intrusion, Metamorphism, and Tectonism in the Anti‐Atlas Mountains », The Journal of Geology, vol. 113, no 4, p. 439‑450, juill. 2005, doi: 10.1086/430242.
[31]      M. Bhilisse, A. Wafik, H. Admou, L. Maacha, et M. Constantin, « Geochemical and Mineralogical Characteristics of Serpentinite and Carbonated Serpentinite: case of Magnesite (Bou Azzer inlier, Central Anti-Atlas, Morocco). », vol. Journal of Tethys, 2, 287–313., 2014.
[32]      M. Souiri et al., « Hydrothermal alterations of the Bou Azzer East Co-Ni-As-Au deposits (central Anti-Atlas, Morocco) », Geosci J, vol. 25, no 5, p. 635‑660, oct. 2021, doi: 10.1007/s12303-020-0063-2.
[33]      E. Hoek et E. T. Brown, « Empirical Strength Criterion for Rock Masses », Journal of the Geotechnical Engineering Division, vol. 106, no 9, p. 1013‑1035, sept. 1980, doi: 10.1061/AJGEB6.0001029.
[34]      J. A. Hudson, Rock mechanics principles in engineering practice. 1989.
[35]      E. Hoek et E. T. Brown, « Practical estimates of rock mass strength », International Journal of Rock Mechanics and Mining Sciences, vol. 34, no 8, p. 1165‑1186, déc. 1997, doi: 10.1016/S1365-1609(97)80069-X.
[36]      E. Hoek, P. Marinos, et M. Benissi, « Applicability of the geological strength index (GSI) classification for very weak and sheared rock masses. The case of the Athens Schist Formation », Bull Eng Geol Environ, vol. 57, no 2, p. 151‑160, sept. 1998, doi: 10.1007/s100640050031.
[37]      P. Marinos et E. Hoek, « Gsi: A Geologically Friendly Tool For Rock Mass Strength Estimation », International Society for Rock Mechanics and Rock Engineering, nov. 2000. https://www.onepetro.org/conference-paper/ISRM-IS-2000-035
[38]      « Rocscience Inc. », Rocscience Inc. Consulté le : 6 décembre 2024. https://www.rocscience.com/software/rocdata/program-updates
[39]      RocScience Inc., « RS2-11.0Z ». (rock and soil 2-dimensional analysis program). Toronto, Canada: RocScience Inc.
[40]      A. Driouch, L. Ouadif, K. Benjmel, M. Bhilisse, et S. Ilmen, « Determining the regional tectonic stress field by remote sensing in the Bou Azzer inlier, Central Anti-Atlas, Morocco », Min. miner. depos., vol. 16, no 2, p. 49‑54, juin 2022, doi: 10.33271/mining16.02.049.
[41]      A. Zang, O. Stephansson, O. Heidbach, et S. Janouschkowetz, « World Stress Map Database as a Resource for Rock Mechanics and Rock Engineering », Geotech Geol Eng, vol. 30, no 3, p. 625‑646, juin 2012, doi: 10.1007/s10706-012-9505-6.
[42]      G. Barla, « Squeezing rocks in tunnels », ISRM News Journal, vol. 2, no 3, p. 44‑49, 1995.
[43]      F. Abbasi, M. H. Khosravi, A. Jafari, A. Bashari, et B. Alipenhani, « Support analysis of main tunnels in Tabas mechanized Parvadeh mine at intersection with coal seam », Journal of Mining and Environment, no Online First, avr. 2021, doi: 10.22044/jme.2021.10610.2014.
[44]      D. U. Deere, « Technical description of rock cores for engineering purpose », Rock Mechanics and Enginee-ring Geology, vol. 1, no 1, p. 17‑22, 1964.
[45]      A. Palmstrom et E. Broch, « Use and misuse of rock mass classification systems with particular reference to the Q-system », Tunnelling and Underground Space Technology, vol. 21, no 6, p. 575‑593, nov. 2006, doi: 10.1016/j.tust.2005.10.005.
[46]      B. Singh et R. K. Goel, Rock mass classification: a practical approach in civil engineering, vol. 46. Elsevier, 1999.
International Journal of Mining and Geo-Engineering

Articles in Press, Accepted Manuscript
Available Online from 09 September 2026