Stabilization Of Waste Dump Materials In Open-Pit Coal Mining Using Chemical Treatment

Abstract Slope instability in open-pit mine waste dumps is commonly attributed to saturated clayey foundation soils, which act as slip surfaces and trigger mass movements. This phenomenon was observed in the present case study, underscoring the need for systematic and effective geotechnical improvement measures. The objectives of this research are to identify the factors contributing to slope instability and to evaluate the effects of soil stabilization using a combination of cement and ion exchange on the improvement of foundation soil mechanical properties and the slope’s factor of safety (FoS). The methodology involved laboratory testing (Unconfined Compressive Strength, elastic modulus, cohesion, and internal friction angle) and the integration of these results into numerical modelling using the Limit Equilibrium Method. Laboratory results indicated that UCS increased from 45 kPa to 1,667 kPa, cohesion increased from 50 kPa to around 145 kPa, and the internal friction angle improved from 30° to 47° at the optimum cement–ion exchange composition. Stability analysis identified pore water pressure as the dominant factor controlling slip surface formation. Implementation of a toe embankment yielded an increase in static FoS from 0.6 to 1.3. This allowing for a height increase from 60 m to 80 m; while a further reduction to 25° permitted a height increase up to 100 m, both maintaining FoS within the safe range. Overall, the combination of chemical stabilization and a toe embankment was proven to enhance the mechanical properties of the foundation soil and the global stability of the slope, while providing design flexibility for height increases under controlled risk.