## 4 Discussion
### Limitations  
The geometry of the stope and drifts are assumed to be vertical, and the secondary drifts are simplified with identical dimensions of the primary drifts in numerical modeling. In practice, the drift walls exhibit irregular geometries and inclinations, and the primary and secondary drifts generally differ in size. The influence of the drift inclination and the varied drift size require further investigation.  
The backfill and rock mass are modeled as homogeneous, isotropic materials obeying the Mohr-Coulomb criterion. In practical stopes, the drift backfill is non-homogeneous and anisotropic due to segregation and the staged filling strategy [16; 36]. The stress-strain behavior of the backfill can be more complicated in plasticity. Furthermore, natural joints and fractures within the rock mass are not accounted for in the current simulation.  
We attempted to validate the numerical simulations by comparing the numerical results with field data obtained from a published study by [PERSON] et al., who conducted field  
Figure 7: Variations in the required UCS of the backfill roof with different drift spans, obtained by numerical simulation and analytical solutions (Equations (3)–(6)), respectively.  
measurements on the overlying load and stress state of the cemented paste backfill roof at the Jinchuan Nickel Mine using underhand drift-and-fill mining [32]. Strain gauges and pressure sensors were installed in the backfill roof at 48# and 40# Stopes to collect the stress and strain data, and further details about the measurement can be found in [PERSON]'s study [32]. The measured overlying load, maximum vertical displacement, and maximum tensile stress of the backfill roof were compared with those obtained from the numerical simulation for the case with drift sizes of 3.5 m \(\times\) 3.0 m, as shown in Figure 8.  
In Figure 8, the maximum tensile stresses from the numerical results align well with those monitored at 48# and 40# Stopes. However, there are noticeable differences in the maximum vertical displacement and overlying load. These discrepancies are understandable because the physical and mechanical parameters, constitutive model, and initial ground stress adopted in the numerical model were not specifically selected based on the Jinchuan Nickel Mine (these parameters are also unavailable in [PERSON]'s study [32]). Nevertheless, as shown in Figure 8, the numerical results and field data remain within a similar order of magnitude, which, to some extent, validates the rationality of the numerical simulation conducted in this study. It is anticipated that further field monitoring at the Maoping Lead-Zinc Mine will allow for the use of parameters that better reflect the specific engineering conditions of the mine, thereby providing additional verification for the numerical simulation.  
This study provides a detailed analysis of the stability of the backfill roof with the basket weave drift layout from a safety perspective. However, it does not explore the practical implications and constructability of this drift layout in terms of mining process convenience, production management, or costs. For this drift layout, the drifts are designed to be perpendicular to those in the upper layer, and then the drift driving directions in the adjacent layers are alternating during stoping. While this design contributes to stability, it not only introduces significant challenges for production management but also complicates the selection of ore pass locations, potentially resulting in higher production costs. Further research is necessary to jointly consider the practical implications and constructability of this layout while optimizing both the drift layout and the strength requirement of the backfill roof.  
Figure 8: Comparison of numerical results with field data measured at Jinchuan Nickel Mine [32].