Engineering Geology

Engineering Geology

A Comprehensive Study on the Effects of Geometric and Geomechanical Parameters on Crown Pillar Behavior during the Transition from Open-Pit to Underground Mining

Authors
Salman Shamsoddini Motlagh
Saeed Mahdavi
Isfahan University of Technology
10.22034/JEG.2026.20.1.101085
Abstract
Due to the deepening of open-pit mines and the associated environmental considerations, the current era has been called the "return to underground mining period." One of the fundamental considerations in the transition from open-pit to underground mining is the design of crown pillars based on economic and technical considerations. As result of uncertainties in this research topic, the present study employs three-dimensional numerical simulation to investigate the interactive effects of geometric and geomechanical parameters on crown pillar behavior during the transition to underground mining. The pillar behavior was evaluated based on displacement magnitude and plastic zone volume of the pillar. The results of the numerical simulation showed that geometric parameters play a much more significant role than rock mechanical properties. Among geometric parameters, the pillar dimension index (product of pillar thickness and span) and crown pillar span have a decisive role in controlling pillar behavior. From a geomechanical perspective, within the range of variations considered in this research, rock elastic modulus was identified as the influential parameter on crown pillar behavior, which controls crown pillar behavior with a critical value of 7 GPa. The crown pillar span, as the second most influential parameter, can predict crown pillar displacement with a correlation coefficient of 0.83, and the pillar dimension index can estimate the plastic zone volume in the pillar with 20% accuracy.

Keywords
Crown pillar
Sensitivity Analysis
underground mining
3D numerical simulation
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