Numerical and experimental studies of the natural mixing behavior between an uncemented paste backfill and dumped waste rock in stopes from laboratory toward field conditions. Part II: Application and prediction of the validated and calibrated numerical model
Yuyu Zhang, Li Li*, Louis-Philippe Gélinas, Serge Ouellet
Deep Resources Engineering. 2026, 3(3): 100236. 
doi.org10.1016j.deepre.2026.100236.pdf
Abstract: Directly dumping waste rocks (WR) underground produced into mine stopes being filled with cemented paste backfill offers several advantages. However, this practice can also present certain risks, especially when the dumping operation is poorly controlled or when the cohesionless WR are not fully or properly mixed with the paste backfill. Therefore, it is critical to understand and well quantify the mixing degree between dumped WR and paste backfill in stopes. To date, however, publications addressing the natural mixing behavior between dumped WR and paste backfill in stopes are almost nonexistent. Moreover, conducting laboratory tests with oversized WR is impractical. Scaling down techniques must be applied to exclude large and oversized particles found in in situ WR. Experimental results obtained using WR samples with different maximum particle sizes (dmax) can then be used to calibrate and validate a numerical model. Once validated and calibrated, the numerical model can be used to evaluate and quantify the mixing degree between dumped WR and paste backfill, while accounting for the size effects of both stopes and WR particles. In this study, a series of laboratory tests were conducted at different scales, varying both the stope size and the particle size of the WR. The validated and calibrated numerical model, presented in the companion paper (Part I), was then applied to predict the experimental results. The model’s reliability is partly confirmed by strong agreement between some numerical prediction and experimental results. Consequently, the validated model can be further applied to simulate the natural mixing behavior of a paste backfill and dumped WR with larger dmax in large-scale scenarios. However, some discrepancies were also observed between certain numerical predictions and test results. These inconsistencies helped identify limitations in both the laboratory testing setup and numerical model itself. As a result, clear directions for future improvements have been established. This study demonstrates the value and potential of numerical modeling as a powerful tool for analyzing the natural mixing behavior in mine backfilling operations.
Highlights:
• The natural mixing behavior of dumped waste rock with paste backfill is reproduced using a DEM-based numerical model.
• All numerical results are predictive, as all model parameters were determined previously without any further calibration.
• Drop tests were conducted with different box sizes and waste rock samples of different dmax using the scalping technique.
• The numerical model captured the natural mixing behavior between uncemented paste backfill and dumped waste rock.
• Mismatches between numerical and experimental results need further thoughtful analysis, not arbitrary parameter calibration.
Keywords: Waste rocks; Paste backfill; Maximum particle size; Natural mixing behavior; Numerical modeling; Size effects
Cite: Zhang, Y.Y.; Li, L.; Gélinas, L.-P.; Ouellet, S., Numerical and experimental studies of the natural mixing behavior between an uncemented paste backfill and dumped waste rock in stopes from laboratory toward field conditions. Part II: Application and prediction of the validated and calibrated numerical model, Deep Resources Engineering 2026, 3 (3), 100236. https://doi.org/10.1016/j.deepre.2026.100236
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