This research was conducted to evaluate the association of rock fragmentation with different unit operations of a sublevel caving (SLC) production cycle. Drilling, charging, and blasting, as well as the nature of the rock mass, can affect the fragmentation observed at the drawpoints. Similarly, loading the blasted material from the drawpoints and dumping to the orepasses are strongly influenced by the nature of the fragmentation, particularly the oversize rock fragments.

The aim of this research was to evaluate the operational and economic impacts of different fragment sizes in a production cycle of an SLC operation. It also investigated the possibility of predicting rock fragmentation in SLC blasting based on the nature of the rock mass.

The required data for this research were collected from LKAB’s Malmberget iron ore mine. The loading operation of the blasted rock was filmed, and images of Load-Haul-Dump (LHD) buckets containing blasted rock were extracted from the video recordings. The blasted rock inside the buckets was categorized as fine, medium, coarse, and oversize fragmentation, based on the median fragment size (X 50 ). Measurement While Drilling (MWD) data were used to classify the rock mass based on the extent of rock fracturing, and statistical analysis was performed to predict the fragmentation. The results showed that the percentage occurrence of fine and medium fragmentation classes and oversize fragments have better correlations and can be better predicted using MWD data than other fragmentation types. The impact of dumping oversize fragments to orepasses with and without a screening device was evaluated. The results showed an increase in the cycle time of the LHD machines for the orepass with the screening infrastructure.

The results suggest that the drill monitoring technique has the potential to predict rock fragmentation, particularly oversize rock fragments. In addition, the variations in fragmentation during loading should be considered to allocate the best resources for handling different fragment sizes properly and improve density-based ore grade estimations. Grizzlies, along with boulder breakers, should be used to prevent oversize fragments from entering the orepasses and to increase the overall productivity of the operation.

Mining is a high-risk industry, so efficiency and safety are key priorities. As mines continue to go deeper and exploit low-grade deposits, bulk mining methods, such as sublevel caving (SLC), have become increasingly important. SLC is suitable for massive steeply dipping ore bodies and is known for its high degree of mechanisation, productivity, and low operational cost. Moreover, technological developments and mechanisation have allowed these methods to be applied at greater depths. In modern mechanised mines Load haul dump (LHD) machines are central to achieving the desired productivity. Therefore, automation of LHDs and their increasing use in mines make it crucial to understand the performance of these machines in actual mining environments. The aim of this research was to understand the differences in the productivity of semiautonomous and manual LHDs and identify how external factors impact the performance of these machines in SLC operations. The research also investigated how LHD operator training could improve the loading efficiency.

Performance data for semi-autonomous and manual LHDs were collected from LKAB’s Kiirunavaara mine’s central database, GIRON. These data were used to compare cycle times and payloads of semi-autonomous and manual LHDs. The data were filtered and sorted so that only data where both machine types were operating in the same area (crosscut, ring, and ore pass) were used. To understand the impact of external factors, data on the occurrence of boulders were collected from LKAB’s Malmberget mine by recording videos of LHD buckets, while the data on operator training were obtained by performing baseline mapping and conducting a questionnaire study with the LHD operators at LKAB’s Kiirunavaara mine.

The results of the comparative analysis of manual and semi-autonomous LHDs showed the mean payload was 0.34 tonnes higher for manual LHD machines. However, the differences were not consistent across different areas of the mine. Similarly, when comparing the cycle times, in 57% of the studied area, manual LHDs had lower cycle time, while the opposite was true in the remaining 43% of the areas. Therefore, the differences in cycle time and payload due to mode of operation are not conclusive, meaning that one machine type does not completely outperform the other. This highlights the importance of understanding the external factors that cause such differences. Moreover, the findings emphasize the need to upgrade LHD operator training based on pedagogical principles and the inclusion of new technologies to enhance loading efficiency and increase overall productivity.