Optimizing blast design and bench geometry for stability and productivity in open pit limestone mines using experimental and numerical approaches.

Optimizing blast design and bench geometry is crucial for enhancing the safety, efficiency, and sustainability of open-pit mining operations. This study examines the effects of blast design and bench geometry adjustments on bench slope stability through numerical modelling under static and dynamic loading conditions. Extensive data on rock mass, blast design parameters, and geomechanical properties were analyzed to assess these optimizations. Results indicate that reducing the bench height from 12 to 5 m improves the shear reduction factor (SRF) by 43.78%, while decreasing the bench face angle (BFA) from 90° to 60° enhances the SRF by 17.12%, demonstrating increased stability. Conversely, increasing the overall slope angle from 27.5° to 36.5° improves productivity by 57.14% but reduces the SRF by 17.12%, highlighting the trade-off between stability and extraction efficiency. Optimal conditions balancing stability and productivity were identified with a bench height of 7.5 m, a BFA of 75°, and a bench width of 14 m, yielding an SRF of 1.31 under static conditions and 1.16 under dynamic conditions. Simulations of blast dynamics revealed that the bench blast velocity decreased from 63.18 cm/s at a radial distance of 13 m to 23.99 cm/s at 18.5 m, indicating significant attenuation in particle motion over distance. Blast-induced ground vibrations (BIGV) were also evaluated, with notable peak particle acceleration near the blast zone. The study recommends a powder factor range of 0.31-0.51 kg/m and a peak particle velocity (PPV) threshold of 30-40 cm/s to optimize blast design while ensuring operational safety. These findings provide critical insights for enhancing stability and productivity in large-scale open-pit limestone mining operations.