article · Mining Technology Transactions of the Institutions of Mining and Metallurgy
Strip mining provides a productive and economical approach for extracting layered mineral deposits, but maintaining highwall stability is critical to its technical viability and safe operational limits. In complex geological settings, such as multilayer phosphate deposits where thin ore seams alternate with waste layers under deepening overburden, stability management becomes particularly demanding. An investigation of a phosphate deposit in Morocco used limit equilibrium modelling to examine how increasing overburden thickness influences highwall stability. The analysis demonstrated that thicker overburden progressively reduces the factor of safety, establishing an upper operational threshold for conventional strip mining techniques. Crucially, when overburden thickness exceeds 20 metres, the dominant mechanism controlling stability changes, causing the critical slip surface to relocate directly into the overburden layer. These insights allow mine planners to anticipate geotechnical hazards and modify extraction designs prior to reaching unstable conditions.
Open-pit strip mining risks catastrophic ground collapse if highwalls are cut too steeply or under excessive overburden weight. Understanding precisely when and where slopes become unstable allows mining engineers to adjust excavation depths and geometry in advance. This prevents costly operational disruptions, protects heavy equipment, and safeguards the workforce in complex layered deposits.
The findings are directly applicable to mine planning teams and geotechnical consultants working on multilayer stratiform deposits, particularly in phosphate extraction. The modelling insights appear applied and ready for immediate operational translation, helping mining companies define safe excavation limits, refine slope designs, and determine when to transition away from conventional strip mining as overburden deepens.
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Strip mining is a cost-effective and high-productivity method that is widely used for the exploitation of stratiform deposits. The assessment of highwall stability is a fundamental requirement that conditions the technical feasibility of this method and determines its operational limits. This paper presents a stability assessment of a complex multilayer phosphate deposit in Morocco, characterised by a tight alternation of phosphate ore seams and waste interlayers combined with progressively increasing overburden thickness. In fact, the stratigraphic analysis of the exploited deposit revealed a progressive increase in overburden thickness in the direction of mining advance, defining the complex geological framework within which the simulation scenarios were built. To evaluate highwall stability under these conditions, a limit equilibrium approach was adopted. The results show that overburden thickening leads to a progressive reduction of the factor of safety which defines a technical limit for conventional strip mining. Another finding is a clear shift in the controlling factor of stability beyond 20 m, where the critical slip surface relocates within the overburden layer. These findings provide a practical basis for the anticipation of geotechnical constraints and the adaptation of mining operations before they reach critical configurations.
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DOI: 10.1177/25726668261473734
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