Optimising ground support for mine tunnelling on the Great Dyke of Zimbabwe using analytical, empirical, and kinematic methods

ABSTRACT: This study develops a comprehensive framework to optimise ground support for mine tunnelling on the Great Dyke of Zimbabwe, an area characterised by significant geological complexity and variability. Employing analytical, empirical, and kinematic methods, the research addresses challenges associated with rockmass instability to ensure operational safety and efficiency. The primary objectives included delineating geotechnical zones through rigorous geological logging, designing suitable support systems tailored to site-specific conditions, and integrating sustainability principles to minimise material waste. The methodologies combined sensitivity analysis of support parameters with Rock Mass Rating (RMR) and Q-system classifications. Kinematic analysis using Rocscience's UnWedge software identified critical wedge instabilities associated with joint set interactions. Results demonstrated that 2.2 m long rockbolts with 80 kN capacity at a spacing of 1.5 m x 1.5 m provided optimal reinforcement, achieving safety factors above 2. Shotcrete thicknesses ranged from 5.5 cm in moderately fractured zones (RMR 66 to 70) to 8 cm in highly fractured zones (RMR 59 to 65), ensuring surface stabilisation. The study highlighted the necessity of pre-tensioned rockbolts for creating stiff roof plates in layered rockmass sections. This multi-method framework significantly contributes to underground support engineering, advancing both theoretical understanding and practical applications for complex geological settings.