Fragmentation and associated fines generation are key processes influencing the productivity and safety of cave mining operations. Despite extensive studies over several decades, the mechanisms and characteristics governing secondary fragmentation and fines generation remain insufficiently understood. This limited understanding is largely due to the inaccessibility of draw columns for direct observation and the constraints of laboratory flow experiments, which typically employ nearly rigid materials under low-stress conditions. This thesis investigates the mechanisms and characteristics of secondary fragmentation through numerical simulations, providing new insights into fragmentation behaviour and associated fines generation under various loading conditions. Numerical simulations incorporating the Flat-Jointed Bonded Particle Model (FJ-BPM) were used to investigate the mechanisms and characteristics of secondary fragmentation. Simulations reveal that arching collapse and erosion are the dominant fragmentation mechanisms in the near-field zone, while confined compression dominates the far-field zone of the muckpile. Furthermore, the study suggests that the near-field region is governed by the passive stress condition, whereas the far-field region is predominantly under the active stress condition. This thesis further examines the mechanisms and characteristics of impact- and compression-induced breakages, which occur when rock blocks fall through air gaps and arches in the near-field, respectively. The results demonstrate that fragmentation characteristics can be interpreted through comminution theory. In addition, one-dimensional confined compression simulations on bulk rock fragments, which is equivalent to loading conditions in far-field zone, reveal how cushioning effects can suppress large-block breakage while simultaneously generating fines. Beyond numerical modelling, the thesis critically evaluates the limitations of input parameters used in current fragmentation models and provides an improved framework for fragmentation analyses. Furthermore, the internal and external sources of fines are systematically summarized to enhance the prediction of fines generation and its implications for cave performance. Overall, this thesis contributes to a deeper mechanistic understanding of secondary fragmentation processes in cave mining and offers practical insights for refining existing fragmentation analysis approaches.
Yalin Li (Thu,) studied this question.