Acquisition setup for rock fragmentation measurement in field conditions

Rock fragmentation is a key determinant of downstream excavation performance in surface mining operations. Among blasting design parameters, stemming depth governs explosive energy confinement; however, its field-scale influence on fragmentation quality and excavation efficiency remains insufficiently quantified. This study experimentally investigates the effect of two stemming depths (3 m and 4 m) on rock fragmentation characteristics and excavator cycle time through controlled field blasting trials conducted in a hard sandstone formation. All blasts were executed using identical drilling geometry, explosive type, and operational procedures, with stemming depth treated as the sole variable. Fragmentation outcomes were quantified using image-based analysis (Split Desktop), while excavator cycle time and its individual components were measured directly during loading operations. Statistical evaluation was performed using descriptive statistics, Mann–Whitney U tests, and one-way analysis of variance (ANOVA). The results show that a 3 m stemming depth produces consistently finer fragmentation, reflected by a lower median fragment size (D50 = 38.1 cm) compared to the 4 m configuration (D50 = 45.6 cm), along with a substantial reduction in oversize fragments (> 50 cm) from 27.9% to 12.4%. Improved fragmentation is associated with a statistically significant reduction in excavator digging time for 3 m stemming (14.2 ± 2.1 s) relative to 4 m stemming (18.6 ± 3.0 s; p = 0.004). In contrast, no statistically significant difference is observed in the mean total excavator cycle time between the two configurations. These findings are limited to a single lithology and blast geometry and should therefore be regarded as conditionally applicable to comparable geological and operational settings. Nevertheless, the study demonstrates that appropriate stemming depth selection can reduce oversize generation and improve excavation smoothness, providing practical, field-based guidance for blast design optimization. Field-scale blasting experiments demonstrate that reducing stemming depth from 4 m to 3 m significantly improves rock fragmentation quality in hard sandstone. A 3 m stemming depth decreases median fragment size (D50) from 45.6 cm to 38.1 cm and reduces oversize fragments (> 50 cm) from 27.9% to 12.4%. Improved fragmentation results in a statistically significant reduction in excavator digging time (from 18.6 ± 3.0 s to 14.2 ± 2.1 s; Mann–Whitney p = 0.004). No statistically significant difference is observed in mean total excavator cycle time, indicating that operational benefits are expressed through reduced variability and smoother excavation rather than faster average cycles. The findings provide site-specific, field-based evidence supporting stemming depth selection as a practical control parameter for improving excavation performance.