## 5 Numerical Calculation Analysis  
The ore body is simulated by FLAC\({}^{\text{3D}}\), and the Mohr-Coulomb model is used as the constitutive model. According to the on-site monitoring data, the design model size is 500 m \(\times\) 400 m \(\times\) 200 m, the average dip angle of the orebody in the simulation area is 40\({}^{\circ}\), and the thickness of the orebody is 40 m. The coordinate axis \(Z\) direction is the vertical direction, the coordinate axis Y direction is along the ore body trend, and the coordinate axis X direction is perpendicular to the ore body trend. During the simulation process, the bottom restricts the movement in the vertical direction, the surroundings of the model restrict the displacement in the horizontal direction, and the model exerts the gravity of the rock mass itself. The model is shown in Figure 12.  
Because the structural planes of the top and bottom layers of the ore body are not developed, various mechanical parameters of the rock are measured through the indoor test method. Through a large number of tests on the samples, various parameters required for numerical simulation are obtained, as shown in Table 3. The settlement effect of different backfilling materials is analyzed by numerical simulation. Figure 11: Paste backfilling slurry state. Figure 12: Numerical model. According to Figure 13, the effects of full tailings cemented backfilling and medium-fine tailings paste backfilling are obtained. When full tailings cemented backfilling is used, the maximum vertical displacement of the overlying strata is 80 mm. When medium-fine tailings paste is used for backfilling, the maximum vertical displacement of the overlying strata is 52 mm, and the maximum displacement of the overlying strata is reduced by 28 mm. The following conclusions can be drawn, the backfilling effect of using medium and fine tailings paste is obviously better than the effect of using full tailings cemented backfilling. The migration effect of the overlying strata is gradually strengthened. Through the analysis of the experimental data, the roof subsidence curves of different filling bodies are obtained. The results are shown in Figure 14.  
Figure 15 shows that the shift from full tailings cemented backfilling to medium and fine tailings paste backfilling causes the support pressure of the backfilling body to become larger, and the pressure on both sides of the ore body to gradually decrease. When full tailings cemented backfilling is used, the peak stress of the backfilling body is 0.1 MPa, and the peak stress of ore bodies on both sides is 0.69 MPa and 0.59 MPa respectively. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Lithology** & **Density** & **Elastic** & **Poisson** & **Cohesion** & **Friction** & **Tension** \\  & **(kg\(\cdot\)m\({}^{-3}\))** & **(GPa)** & **Ratio** & **(MPa)** & **(\({}^{\prime}\))** & **(MPa)** \\ \hline Top Plate & 2700 & 12.54 & 0.22 & 1.4 & 33 & 2.6 \\ \hline Mine & 2780 & 8.72 & 0.23 & 1.2 & 32 & 2.4 \\ \hline Bottom Plate & 2700 & 15.36 & 0.20 & 2.0 & 34 & 3.5 \\ \hline Backfilling Body & 2100 & 0.009 & 0.26 & 0.5 & 24 & 0.16 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Model calculation mechanics parameter list. Figure 14: The roof subsidence curves of different backfilling bodies. Figure 13: Cloud diagram of vertical displacement of overlying rock of different backfilling bodies. (**a**) Full tailings cemented backfilling and (**b**) Medium and fine tailings paste backfilling. To sum up, during the transition from full tailings cementation backfilling to medium and fine tailings paste backfilling, the deformation of the backfilling body and ore body gradually decreases, the gravity distribution of the overlying rock gradually becomes uniform, and the stress concentration area of the overlying rock gradually transfers to the backfilling body. Figure 16 shows that when the full tailings are cemented and filled, the plastic zone is destroyed in a very small range.